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About fracture mechanics

2009-05-12T04:21:55Z

24.113.151.15: /* See also */

'''Fracture mechanics''' is the field of [[mechanics]] concerned with the study of the formation of cracks in materials. It uses methods of analytical [[solid mechanics]] to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to [[fracture]].

In modern [[materials science]], fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the [[physics]] of [[stress (physics)|stress]] and [[Strain (materials science)|strain]], in particular the theories of [[Elasticity (physics)|elasticity]] and [[plasticity (physics)|plasticity]], to the microscopic [[crystallographic defect]]s found in real materials in order to predict the macroscopic mechanical failure of bodies. [[Fractography]] is widely used with fracture mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures.

==The need for fracture mechanics==
[[File:Tay1.jpg|thumb|right|Tay Bridge Disaster (1879)]]

In many cases, failure of engineering structures through fracture can be fatal; one example is that of the [[Tay Rail Bridge disaster]] (right). Often disasters occur because engineering structures contain cracks—arising either during production or during service (e.g. from [[Fatigue (material)|fatigue]]). For instance, growth of cracks in pressure vessels due to crack propagation could cause a fatal explosion. If failure were ever to happen, we would rather it were by [[yield (engineering)|yield]] or by leak before break.

[[File:CrackForceLines.gif|thumb|right|Internal [[force lines]] are denser in the crack tips]]

Since cracks can lower the strength of the structure beyond that due to loss of load-bearing area a material property, above and beyond conventional strength, is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics—the evaluation of the strength of cracked structures.

==History==
===Griffith's energy relation===
[[File:EdgeCrack2D.png|thumb|right|An edge crack (flaw) of length <math>a</math>in a material.]]

Fracture mechanics was invented during World War I by English aeronautical engineer, [[Alan Arnold Griffith|A. A. Griffith]], to explain the failure of brittle materials.<ref>{{Citation | last = Griffith | first = A. A. | author-link = Alan Arnold Griffith | title = The phenomena of rupture and flow in solids | journal = Philosophical Transactions of the Royal Society of London | series = A | volume = 221 | pages = 163–198 | year = 1921 | url = http://www.cmse.ed.ac.uk/AdvMat45/Griffith20.pdf}}.</ref> Griffith's work was motivated by two contradictory facts:

* The stress needed to fracture bulk [[glass]] is around {{convert|100|MPa|psi|abbr=on}}.
* The theoretical stress needed for breaking atomic bonds is approximately {{convert|10000|MPa|psi|abbr=on}}.

A theory was needed to reconcile these conflicting observations. Also, experiments on glass fibers that Griffith himself conducted suggested that the fracture stress increases as the fiber diameter decreases. Hence the uniaxial tensile strength, which had been used extensively to predict material failure before Griffith, could not be a specimen-independent material property. Griffith suggested that the low fracture strength observed in experiments, as well as the size-dependence of strength, was due to the presence of microscopic flaws in the bulk material.

To verify the flaw hypothesis, Griffith introduced an artificial flaw in his experimental specimens. The artificial flaw was in the form of a surface crack which was much larger than other flaws in a specimen. The experiments showed that the product of the square root of the flaw length (''a'') and the stress at fracture (''σ''f) was nearly constant, which is expressed by the equation:

:<math>\sigma_f\sqrt{a} \approx C</math>

An explanation of this relation in terms of linear elasticity theory is problematic. Linear elasticity theory predicts that stress (and hence the strain) at the tip of a sharp flaw in a linear [[elastic deformation|elastic]] material is infinite. To avoid that problem, Griffith developed a [[thermodynamic]] approach to explain the relation that he observed.

The growth of a crack requires the creation of two new surfaces and hence an increase in the [[surface energy]]. Griffith found an expression for the constant ''C'' in terms of the surface energy of the crack by solving the elasticity problem of a finite crack in an elastic plate. Briefly, the approach was:

* Compute the [[potential energy]] stored in a perfect specimen under an uniaxial tensile load.
* Fix the boundary so that the applied load does no work and then introduce a crack into the specimen. The crack relaxes the stress and hence reduces the [[elastic energy]] near the crack faces. On the other hand, the crack increases the total surface energy of the specimen.
* Compute the change in the [[free energy]] (surface energy − elastic energy) as a function of the crack length. Failure occurs when the free energy attains a peak value at a critical crack length, beyond which the free energy decreases by increasing the crack length, i.e. by causing fracture. Using this procedure, Griffith found that

:<math>C = \sqrt{\cfrac{2E\gamma}{\pi}}</math>

where ''E'' is the Young's modulus of the material and ''γ'' is the surface energy density of the material. Assuming ''E'' = 62 GPa and ''γ'' = 1 J/m2 gives excellent agreement of Griffith's predicted fracture stress with experimental results for glass.

===Irwin's modification of Griffith's energy relation===
[[File:PlasticZone2D.png|400px|thumb|right|The plastic zone around a crack tip in a ductile material.]]

<blockquote>
''Griffith's work was largely ignored by the engineering community until the early 1950s. The reasons for this appear to be (a) in the actual structural materials the level of energy needed to cause fracture is orders of magnitude higher than the corresponding surface energy, and (b) in structural materials there are always some inelastic deformations around the crack front that would make the assumption of linear elastic medium with infinite stresses at the crack tip highly unrealistic.'' '''F. Erdogan (2000)'''<ref name=Erdogan00>E. Erdogan (2000) ''Fracture Mechanics'', International Journal of Solids and Structures, 27, pp. 171–183.</ref>
</blockquote>

Griffith's theory provides excellent agreement with experimental data for [[brittle]] materials such as glass. For [[ductile]] materials such as [[steel]], though the relation <math> \sigma_y\sqrt{a} = C </math> still holds, the surface energy (''γ'') predicted by Griffith's theory is usually unrealistically high. A group working under [[G. R. Irwin]]<ref name=Irwin57>Irwin G (1957), ''Analysis of stresses and strains near the end of a crack traversing a plate'', Journal of Applied Mechanics 24, 361–364.</ref> at the U.S. Naval Research Laboratory (NRL) during World War II realized that plasticity must play a significant role in the fracture of ductile materials.

In ductile materials (and even in materials that appear to be brittle<ref>Orowan, E., 1948. ''Fracture and strength of solids''. Reports on Progress in Physics XII, 185–232.</ref>), a [[plastic]] zone develops at the tip of the crack. As the applied [[Structural load|load]] increases, the plastic zone increases in size until the crack grows and the material behind the crack tip unloads. The plastic loading and unloading cycle near the crack tip leads to the [[dissipation]] of [[energy]] as [[heat]]. Hence, a dissipative term has to be added to the energy balance relation devised by Griffith for brittle materials. In physical terms, additional energy is needed for crack growth in ductile materials when compared to brittle materials.

Irwin's strategy was to partition the energy into two parts:
* the stored elastic strain energy which is released as a crack grows. This is the thermodynamic driving force for fracture.
* the dissipated energy which includes plastic dissipation and the surface energy (and any other dissipative forces that may be at work). The dissipated energy provides the thermodynamic resistance to fracture. Then the total energy dissipated is

:<math>G = 2\gamma + G_p</math>

where ''γ'' is the surface energy and ''G''p is the plastic dissipation (and dissipation from other sources) per unit area of crack growth.

The modified version of Griffith's energy criterion can then be written as

:<math>\sigma_f\sqrt{a} = \sqrt{\cfrac{E~G}{\pi}}.</math>

For brittle materials such as glass, the surface energy term dominates and <math>G \approx 2\gamma = 2 \,\, J/m^2</math>. For ductile materials such as steel, the plastic dissipation term dominates and <math>G \approx G_p = 1000 \,\, J/m^2</math>. For [[polymers]] close to the [[glass transition]] temperature, we have intermediate values of <math>G \approx 2-1000 \,\, J/m^2</math>.

=== Stress intensity factor ===
Another significant achievement of Irwin and his colleagues was to find a method of calculating the amount of energy available for fracture in terms of the asymptotic stress and displacement fields around a crack front in a linear elastic solid.<ref name="Irwin57" /> This asymptotic expression for the stress field around a crack tip is

:<math>\sigma_{ij} \approx \left(\cfrac{K}{\sqrt{2\pi r}}\right)~f_{ij}(\theta)</math>

where ''σ''ij are the Cauchy stresses, ''r'' is the distance from the crack tip, ''θ'' is the angle with respect to the plane of the crack, and ''f''ij are functions that are independent of the crack geometry and loading conditions. Irwin called the quantity ''K'' the ''[[stress intensity factor]]''. Since the quantity ''f''ij is dimensionless, the stress intensity factor can be expressed in units of <math>\text{Pa-}\sqrt{\text{m}}</math>.

=== Strain energy release rate ===
Irwin was the first to observe that if the size of the plastic zone around a crack is small compared to the size of the crack, the energy required to grow the crack will not be critically dependent on the state of stress at the crack tip.<ref name="Erdogan00"/> In other words, a purely elastic solution may be used to calculate the amount of energy available for fracture.

The energy release rate for crack growth or ''strain energy release rate'' may then be calculated the change in elastic strain energy per unit area of crack growth, i.e.,

:<math>G := -\left[\cfrac{\partial U}{\partial a}\right]_P = -\left[\cfrac{\partial U}{\partial a}\right]_u</math>

where ''U'' is the elastic energy of the system and ''a'' is the crack length. Either the load ''P'' or the displacement ''u'' can be kept fixed while evaluating the above expressions.

Irwin showed that for a [[fracture#Crack separation modes|mode I crack]] the strain energy release rate and the stress intensity factor are related by:
:<math>
G = G_I = \begin{cases} \cfrac{K_I^2}{E} & \text{plane stress} \\
\cfrac{(1-\nu^2) K_I^2}{E} & \text{plane strain} \end{cases}
</math>
where ''E'' is the [[Young's modulus]], ''ν'' is [[Poisson's ratio]], and ''K''I is the [[stress intensity factor]] in mode I. Irwin also showed that the strain energy release rate of a planar crack in a linear elastic body can be expressed in terms of the mode I, [[fracture#Crack separation modes|mode II]], and [[fracture#Crack separation modes|mode III]] stress intensity factors for the most general loading conditions.

Next, Irwin adopted the additional assumption that the size and shape of the energy dissipation zone remains approximately constant during brittle fracture. This assumption suggests that the energy needed to create a unit fracture surface is a constant that depends only on the material. This new material property was given the name ''[[fracture toughness]]'' and designated ''G''Ic. Today, it is the related quantity ''K''Ic which is called the fracture toughness and is now universally accepted as the defining material property in linear elastic fracture mechanics.

=== Limitations of linear elastic fracture mechanics ===
[[File:TankerSchenectady.jpg|thumb|right|The [[S.S. Schenectady|S.S. ''Schenectady'']] split apart by [[brittle fracture]] while in harbor (1944)]]

But a problem arose for the NRL researchers because naval materials, e.g., ship-plate steel, are not perfectly elastic but undergo significant [[plastic deformation]] at the tip of a crack. One basic assumption in Irwin's linear elastic fracture mechanics is that the size of the plastic zone is small compared to the crack length. However, this assumption is quite restrictive for certain types of failure in structural steels though such steels can be prone to brittle fracture, which has led to a number of catastrophic failures.

Linear-elastic fracture mechanics is of limited practical use for structural steels for another more practical reason. Fracture toughness testing is very expensive and engineers believe that sufficient information for selection of steels can be obtained from the simpler and cheaper [[Charpy impact test]].{{Fact|date=May 2008}}

==Elastic-plastic fracture mechanics==
[[File:Aircraft Crash.jpg|thumb|right|[[Vertical stabilizer]], which separated from the aircraft leading to a fatal crash(2001)]]

Most engineering materials show some inelastic behavior under operating conditions that involve large loads.{{Fact|date=June 2008}} In such materials the assumptions of linear elastic fracture mechanics may not hold, that is,
* the plastic zone at a crack tip may have a size of the same order of magnitude as the crack size
* the size and shape of the plastic zone may change as the applied load is increased and also as the crack length increases.

Therefore a more general theory of crack growth is needed for elastic-plastic materials that can account for:
* the local conditions for initial crack growth which include the nucleation, growth, and coalescence of voids or decohesion at a crack tip.
* a global energy balance criterion for further crack growth and unstable fracture.

=== R-curve ===
An early attempt in the direction of elastic-plastic fracture mechanics was [[G. R. Irwin|Irwin's]] '''crack extension resistance curve''' or '''R-curve'''. This curve acknowledges the fact that the resistance to fracture increases with growing crack size in elastic-plastic materials. The R-curve is a plot of the total energy dissipation rate as a function of the crack size and can be used to examine the processes of slow stable crack growth and unstable fracture. However, the R-curve was not widely used in applications until the early 1970s. The main reasons appear to be that the R-curve depends on the geometry of the specimen and the crack driving force may be difficult to calculate.<ref name="Erdogan00"/>

=== J-integral ===
In the mid-1960s [[James R. Rice]] (then at [[Brown University]]) and G. P. Cherepanov independently developed a new toughness measure to describe the case where there is sufficient crack-tip deformation that the part no longer obeys the linear-elastic approximation. Rice's analysis, which assumes non-linear elastic (or monotonic [[deformation-theory]] [[plastic]]) deformation ahead of the crack tip, is designated the [[J integral]].<ref>{{Citation | last = Rice | first = J. R. | author-link = James R. Rice | title = A path independent integral and the approximate analysis of strain concentration by notches and cracks | journal = Journal of Applied Mechanics | volume = 35 | pages = 379–386 | year = 1968 | url = http://esag.harvard.edu/rice/015_Rice_PathIndepInt_JAM68.pdf}}.</ref> This analysis is limited to situations where plastic deformation at the crack tip does not extend to the furthest edge of the loaded part. It also demands that the assumed non-linear elastic behavior of the material is a reasonable approximation in shape and magnitude to the real material's load response. The elastic-plastic failure parameter is designated JIc and is conventionally converted to KIc using Equation (3.1) of the Appendix to this article. Also note that the J integral approach reduces to the Griffith theory for linear-elastic behavior.

==Fully plastic fracture mechanics==
If the alloy is so tough that the yielded region ahead of the crack extends to the far edge of the specimen before fracture, the crack is no longer an [[effective stress]] concentrator. Instead, the presence of the crack merely serves to reduce the load-bearing area. In this regime the failure stress is conventionally assumed to be the average of the yield and ultimate strengths of the alloy.

==Engineering applications==
The following information is needed for a fracture mechanics prediction of failure:
*Applied load
*Residual stress
*Size and shape of the part
*Size, shape, location, and orientation of the crack

Usually not all of this information is available and conservative assumptions have to be made.

Occasionally post-mortem fracture-mechanics analyses are carried out. In the absence of an extreme overload, the causes are either insufficient toughness (KIc) or an excessively large crack that was not detected during routine inspection.

==Short summary==
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics is the analysis of flaws to discover those that are safe (that is, do not grow) and those that are liable to propagate as cracks and so cause [[structural failure|failure]] of the flawed structure. Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. There is a high demand for engineers with fracture mechanics expertise—particularly in this day and age where engineering failure is considered 'shocking' amongst the general public.

==Appendix: mathematical relations==
===Griffith's crack theory: strain energy release rate===
For the simple case of a thin rectangular plate with a crack perpendicular to the load Griffith’s theory becomes:

:<math>G = \frac{\pi \sigma^2 a}{E}\,</math>                 (1.1)

where <math>G</math> is the strain energy release rate, <math>\sigma</math> is the applied stress, <math>a</math> is half the crack length, and <math>E</math> is the [[Young’s modulus]]. The strain energy release rate can otherwise be understood as: ''the rate at which energy is absorbed by growth of the crack''.

However, we also have that:

:<math>G_c = \frac{\pi \sigma_f^2 a}{E}\,</math>                 (1.2)

If <math>G</math> ≥ <math>G_c</math>, this is the criterion for which the crack will begin to propagate.

===Irwin's modified Griffith crack theory: fracture toughness===
Eventually a modification of Griffith’s solids theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface weakness energy. Both of these terms are simply related to the energy terms that Griffith used:

:<math>K_I = \sigma \sqrt{\pi a}\,</math>                 (2.1)

and

:<math>K_c = \sqrt{E G_c}\,</math> (for [[plane stress]])                 (2.2)

:<math>K_c = \sqrt{\frac{E G_c}{1 - \nu^2}}\,</math> (for [[plane strain]])                 (2.3)

where ''K''I is the [[stress intensity]], ''Kc'' the fracture toughness, and <math>\nu</math> is Poisson’s ratio. It is important to recognize the fact that fracture parameter ''K''c has different values when measured under plane stress and plane strain

Fracture occurs when <math>K_I \geq K_c</math>. For the special case of plane strain deformation, <math>K_c</math> becomes <math>K_{Ic}</math> and is considered a material property. The subscript I arises because of the different ways of loading a material to enable a crack to propagate. It refers to so-called "mode I" loading as opposed to mode II or III:

[[File:Fracture modes v2.svg|thumb|The three fracture modes.]]

There are three ways of applying a force to enable a crack to propagate:

*'''Mode I crack''' – Opening mode (a [[tensile stress]] normal to the plane of the crack)
*'''Mode II crack''' – Sliding mode (a [[shear stress]] acting parallel to the plane of the crack and perpendicular to the crack front)
*'''Mode III crack''' – Tearing mode (a [[shear stress]] acting parallel to the plane of the crack and parallel to the crack front)

We must note that the expression for <math>K_I</math> in equation 2.1 will be different for geometries other than the center cracked plate, as discussed in the article on [[stress intensity]]. Consequently, it is necessary to introduce a [[dimensionless number|dimensionless correction factor]], ''Y'', in order to characterize the geometry. We thus have:

:<math>K_I = Y \sigma \sqrt{\pi a}\,</math>                 (2.4)

where ''Y'' is a function of the crack length and width of sheet given by:

:<math>Y \left ( \frac{a}{W} \right ) = \sqrt{\sec\left ( \frac{\pi a}{W} \right )}\,</math>                 (2.5)

for a sheet of finite width ''W'' containing a through-thickness crack of length 2''a'', or

:<math>Y \left ( \frac{a}{W} \right ) = 1.12 - \frac{0.41}{\sqrt \pi} \frac{a}{W} + \frac{18.7}{\sqrt \pi} \left ( \frac{a}{W} \right )^2 - \cdots\,</math>                 (2.6)

for a sheet of finite width ''W'' containing a through-thickness edge crack of length ''a''

===Elastic-plastic fracture mechanics theory===
Since engineers became accustomed to using ''K''Ic to characterise fracture toughness, a relation has been used to reduce ''J''Ic to it:

:<math>K_{Ic} = \sqrt{E^* J_{Ic}}\,</math>          where <math>E^* = E</math> for plane stress and <math>E^* = \frac{E}{1 - \nu^2}</math> for plane strain          (3.1)

The remainder of the mathematics employed in this approach is interesting, but is probably better summarised in external pages due to its complex nature.

==See also==
*[[AFGROW]] - Fracture mechanics and fatigue crack growth analysis software
*[[Fracture toughness]]
*[[fatigue (material)|Fatigue]]
*[[Peridynamics]] (a numerical method to solve fracture mechanics problems)
*[[Strength of glass]]
*[[Strength of materials]]
*[[Stress corrosion cracking]]
*[[Stress intensity factor]]
*[[Strain energy release rate]]

==References==
===Notes===
{{reflist}}

===Other reading===

* Davidge, R.W., Mechanical Behavior of Ceramics, Cambridge Solid State Science Series, (1979)

* Lawn, B.R., Fracture of Brittle Solids, Cambridge Solid State Science Series, 2nd Edn. (1993)

* Green, D., An Introduction to the Mechanical Properties of Ceramics, Cambridge Solid State Science Series, Eds. Clarke, D.R., Suresh, S., Ward, I.M. (1998)

===Bibliography===

*C. P. Buckley, "Material Failure", Lecture Notes (2005), [[University of Oxford]].
*T. L. Anderson, "Fracture Mechanics: Fundamentals and Applications" (1995) CRC Press.

==External links==
*[http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_intro.cfm eFunda – Fracture Mechanics]
*[http://hdl.handle.net/1813/3075 Fracture Mechanics Notes] by Prof. Alan Zehnder (from Cornell University)
*[http://imechanica.org/node/755 Nonlinear Fracture Mechanics Notes] by Prof. John Hutchinson (from Harvard University)
*[http://imechanica.org/node/903 Notes on Fracture of Thin Films and Multilayers] by Prof. John Hutchinson (from Harvard University)
*[http://www.seas.harvard.edu/suo/papers/17.pdf Mixed mode cracking in layered materials] by Profs. John Hutchinson and Zhigang Suo (from Harvard University)
*[http://www.mate.tue.nl/~piet/edu/frm/sht/bmsht.html Fracture Mechanics] by Prof. Piet Schreurs (from TU Eindhoven, Netherlands)
*[http://www.dsto.defence.gov.au/publications/1880/DSTO-GD-0103.pdf Introduction to Fracture Mechanics] by Dr. C. H. Wang (DSTO – Australia)
*[http://imechanica.org/node/2621 Fracture mechanics course notes] by Prof. Rui Huang (from Univ. of Texas at Austin)

[[Category:Fracture mechanics| ]]
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[[ja:破壊力学]]
[[ru:Механика разрушения твёрдых тел]]
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Archive:Types of gestures

2007-11-30T04:22:14Z

24.113.30.224: /* Whoop-Dee-Doo */

{{unreferenced||article|date=September 2006}}
Gestures are a form of [[Body language]] or [[Non-verbal communication]].
Although some [[gesture]]s, such as the ubiquitous act of [[Hand gesture|pointing]], differ little from one place to another, most gestures do not have invariable or universal meanings, having specific connotations only in certain cultures. Different types of gestures are distinguished. The most famous type of gestures are the so-called emblems or quotable gestures (see the examples below). These are [[culture]] specific gestures that can be used as replacement for words. Communities have repertoires of such gestures. A single emblematic gesture can have very different significance in different cultural contexts, ranging from complimentary to highly offensive.

Another type of gestures are the ones we use when we speak. These gestures are closely coordinated with speech. The meaningful part of the gesture is temporally synchronised with the co-expressive words. For example, a gesture that depicts the act of throwing will be synchronous with the word 'threw' in the utterance "and then he threw the ball right into the window." Other gestures like the so-called beat gestures, are used in conjunction with speech, keeping time with the rhythm of speech and to emphasize certain words or phrases. These types of gestures are integrally connected to speech and thought processes.

==Studies of gesture==
The first full-length study of gesture was published by [[John Bulwer]] in 1644. Bulwer analyzed dozens of gestures, and provided a guide on how to use gestures to increase eloquence and clarity for public speaking. Today, one of the most prominent researchers in the field of gesture research is [[Adam Kendon]]. He has investigated many aspects of gestures, including their role in communication, conventionalization of gesture, integration of gesture and speech, and the evolution of language. Other prominent researchers in this field include [[Susan Goldin-Meadow]] and [[David McNeill]].

==Social significance==
[[Image:VitarkaMudra.JPG|thumb|right|200px|Vitarka [[mudra]], [[Tarim Basin]], 9th century.]]

Gestures play a major role in many aspects of human life. Many animals, including humans, use gestures to initiate a [[Courtship|mating ritual]]. This may include elaborate [[dance]]s and other movements.

Religious and spiritual gestures are also common, such as the [[Christianity|Christian]] [[sign of the cross]]. In [[Hinduism]] and [[Buddhism]], a ''[[mudra]]'' ([[Sanskrit]], meaning either "posture" or "currency" depending on the interpretation) is a symbolic gesture made with the hand or fingers. Each mudra has a specific meaning, playing a central role in Hindu and Buddhist [[iconography]]. An example is the Vitarka mudra, the gesture of discussion and transmission of Buddhist teaching. It is done by joining the tips of the thumb and the index together, while keeping the other fingers straight.

==Using one hand==
{{main|Hand gesture}}
===Itching Under The Chin===
In Italian culture this represents "I don't care, I can't be bothered". This is done by keeping one hand straight, placing it under the chin, and 'throwing out' that hand toward the person receiving the gesture. In Italian American culture this represents "Screw You!"; U.S. Supreme Court justice [[Antonin Scalia]] received criticism for using this gesture towards a reporter.

Scratching or stroking the chin or beard (where possible) can be used to indicate that the gesticulater is thinking or puzzled.
In the UK, an "itchy chin" can be used to indicate that the person receiving the gesture is lying or talking nonsense, [[bullshit]], in other words. In the UK scratching the chin as a way of implying that the speaker is talking nonsense is often accompanied with any or all of the phrases "reck-on", "chinnus magnus" and "jimmy hill" in no particular order.

===Bang bang===
[[Image:gesture thumb up then down forefinger out like gun.jpg|thumb|right|200px|This gesture mimes a [[handgun]].]]

The "bang bang" gesture is performed by raising the fist with the index finger and thumb extended. The index finger points at the recipient. The thumb is then brought down on top of the fingers. This imitation of the action of a revolver [[pistol]] is often meant to represent a [[handgun]] in children's games. It may also be used menacingly to mean "I'm gonna kill you", or simply as a playful greeting. The middle finger is often also extended to widen the "barrel".

[[Texas Tech University|Texas Tech]] fans use the "bang bang" salute (fingers pointed upward) to cheer their team. Also, the "bang bang" performed with both hands was a signature gesture of [[professional wrestling|professional wrestler]] [[Mick Foley]] while he was in his "Cactus Jack" [[gimmick (professional wrestling)|persona]].

Also, if the thumb and middle finger are used to click, and the thumb the pointed upwards to form the gun, this can also be interpreted as a greeting.

A two-handed version of the same gesture can be used to indicate sporting/business success or sexual conquest (frequently accompanied by a syncopated "pow-pow", esp. in a posh British accent).

=== Beckoning sign ===
Index finger sticking out of the clenched fist, palm facing the gesturer. The finger moves repeatedly towards the gesturer (in a hook) as to draw something nearer. It has the general meaning of "come here", although it is normally seen as condescending or anyway impolite. It is sometimes performed with the four fingers, with the entire hand, or even with the arm, depending on how far the recipient of the sign is.

When performed with the index finger, it may have a mild sexual connotation depending on the circumstance.

In [[Africa]], the [[Far East]] and many [[Spanish language|Spanish]]-speaking countries, this sign is given with all four fingers and with the palm down.

In [[Japan]] there is a similar gesture, but the four fingers are used, the palm faces the recipient and the hand is at head's height. This is the gesture featured in the [[maneki neko]].

===Benediction and blessing===
[[Image:ConstantineCoin.jpg|thumb|right|200px|Benediction gesture, on a coin of [[Constantine I (emperor)|Emperor Constantine]].]]

The benediction gesture is a raised right hand with the ring and pinky fingers touching the palm, while the middle and index fingers remain raised. Taken from Ancient Roman iconography for speaking (an example is the Augustus of Prima Porta where the emperor Augustus assumes the pose of an orator in addressing his troops), it is used as a simple [[charm]] or [[blessing]] amongst many [[neopagan|modern]] [[Paganism|Pagans]], and has a vast array of uses. Perhaps the most common and/or noteworthy use of the gesture is while tracing an invisible "air [[pentagram]]" before someone during certain [[Wicca]]n rituals such as the [[Great Rite]] performed during [[Beltane]] and [[Drawing down the Moon (ritual)|Drawing Down the Moon]] on the [[Esbat]]s. One might also use the gesture to trace invisible pentagrams or other sigils over items to be blessed or empowered, such as [[holy water]], [[ritual]] [[wine]], ritual [[ale]], or [[cannabis|the Sacred Herb]]. The two extended fingers are used to point (except when an [[athame]], [[wand]], or [[sword]] is used).

A similar sign, called the ''benediction'' gesture, is used by the [[Christianity|Christian]] [[clergy]] to perform [[blessing]]s with the [[sign of the cross]]; however Christians keep the thumb raised - the three raised fingers (index, middle, and thumb) are frequently allegorically interpreted as representing the three Persons of the [[Holy Trinity]]. It was shown by representations of [[Jesus]] as [[Christ Pantocrator]].

===Blah-blah===
The fingers are kept straight and together in a horizontal fashion while the thumb is held out straight. The fingers and thumb then snap together repeatedly to suggest a mouth talking. It is used to indicate contempt for a person talking for an excessive period of time about nothing the gesturer feels is important.

===Check, please===
This gesture, understood by waiters around the world to mean that a dinner patron wishes to pay the bill and depart, is executed by touching the index finger and thumb together and "writing" a wavy line in the air, as if to sign one's name. An alternate gesture with the same meaning is made by touching the index finger and thumb together and drawing a [[Tick (checkmark)|checkmark]] ({{unicode|<big>✓</big>}}) in the air. In [[Egypt]], the left hand is held palm-out and the right, palm-down, is tapped against the left wrist to request the check. In [[Thailand]], one makes a circling gesture with the thumb and fingers pinched together- as if you are holding an imaginary pencil and making imaginary scribbles on a piece of paper. Sometimes the opposite palm is used as the 'paper'. In the [[Philippines]], one outlines a rectangle in the air using the thumb and forefinger of both hands.

===Clenched fist===
A raised, clenched fist is used as a gesture of defiance by a number of groups. It is usually considered to be hostile, yet without any sexual, scatological, or notionally offensive connotations. It is especially associated with [[Communism|Communists]] and with other nationalist or ethnic [[revolution]]ary or would-be revolutionary movements, and with the [[Black Power]] movements of the [[1960s]] in the United States. It is the custom to make this gesture while singing ''[[The Internationale]]'', the [[Marxism|Marxist]] anthem. A clenched fist raised quickly up and down and then punched in some direction also signifies a military call for a heavy weapons team to close on the gesturer or to move or open fire in the direction indicated by the punch. In US military, a closed right hand fist raised up with a straight arm with the finger side towards the receiver is an order for the person to stop immediately - to "freeze".<ref>[http://www.truthout.org/docs_2006/071007D.shtml Truthout.org]</ref>

: See also: [[With a strong hand and an outstretched arm]]

=== Pound fist ===
Pound fist is a greeting, in which two individuals touch fists.

=== Clinton thumb ===
The gesture dubbed the "Clinton thumb" after its most famous user, [[Bill Clinton]], is used by politicians to provide emphasis in speeches without pointing the finger. This gesture has the thumb leaning against the thumbside portion of the index finger, which is part of a closed fist. It does not exhibit the anger of the clenched fist or pointing finger, and so is thought to be less threatening. This gesture was likely adopted by Clinton from [[John F. Kennedy]], who can be seen using it in many speeches during his political career.{{Fact|date=February 2007}} It is often used in extemporaenous speech and debate, as a tool for emphasizing points.

===Crossed fingers===
{{main|Crossed fingers}}
A gesture made by crossing the index and middle fingers such that the middle finger overlaps and intertwines the index finger, which can be used to signify one's hope that something should succeed (compare to the phrase "Keep your fingers crossed."). According to OldSuperstitions.com, this stems from the [[superstition]] that "Bad luck is trapped at the point where the two fingers meet so when we cross our fingers, we stop the bad luck from escaping and allow our wishes to come true.". However, if placed behind one's back, the gesture takes on an entirely different meaning: it is then normally used to indicate that the user secretly wishes for something ''contrary'' to what is being stated or going on, or that a lie is being told. This usage is often seen in dramatic contexts.

===Cuckoo sign===
A gesture made by closing ones fist, extending the index finger, and circling it around ones ear for several seconds. This gesture is used to indicate that someone is speaking nonsense or is crazy (more colloquially, this is described as being [[cuckoo]]). The "cuckoo" sign is well-known in the United States.

===Fig sign===
[[Image:gesture fist with thumb through fingers.jpg|thumb|right|200px|The "fig sign" is an ancient gesture with many uses.]]

The "fig sign" is a gesture made with the hand and fingers curled and the thumb thrust between the middle and index fingers, or, rarely, the middle and ring fingers, forming the fist so that the thumb partly pokes out. In some areas of the world, the gesture is considered a good luck charm, in others it is considered an obscene gesture, and in still others it is used in the "I've got your nose!" child's game. This gesture is also the letter "T" in the [[American Sign Language alphabet]]. In [[International Sign]], which otherwise uses the same manual alphabet, "T" has been modified to avoid possible offense.

In [[ancient Rome]], this gesture was called the ''mano fico'', and was a fertility and good luck charm designed to ward off evil. Although this usage has survived in [[Brazil]], where carved images of hands in this gesture are used in good luck [[Amulet|talisman]]s, in many other cultures, such as Greece, Indonesia, Turkey, Cyprus and Russia, the sign has come to have an insulting meaning roughly equivalent to "screw you", based on the thumb being seen as representing a [[clitoris]] or [[sexual intercourse]]. In modern Russia this gesture is used mostly by kids with the meaning "screw you/no way". The same meaning is expressed by adults either with bent elbow (rude, very emphatic, non-classy), or with a "finger" (used mostly by city dwellers). The "finger" made it to Russian gesture language from Western movies. In modern [[Italian language|Italian]], the gesture is called the ''mano fica'', taken to mean "fig hand", as the Italian word for "[[fig]]" is ''fico'' (''ficus'' in [[Latin]]). The obscene connotations of the gesture may partly originate from the fact that a similar Italian word, ''fica'', is a slang term referring to the [[vulva]]. This sexual connotation may date back to ancient Roman times; some Roman amulets combine a ''[[phallus]]'' and a ''mano fico'' gesture. In [[Dante Alighieri|Dante]]'s ''[[Divine Comedy#Inferno|Inferno]]'', [[Vanni Fucci]] curses [[God]] with a "fig" gesture. [http://danteworlds.laits.utexas.edu/circle8b.html#vanni]

Also known as the [[Sicilian Fist]] in Sicily, worn as a good luck charm. * [http://www.italybyvip.com/1874.html Images of the "Sicilian Fist Charm" in Sicily]

The gesture is also used in a trick played by adults and parents, with the intention of convincing their child that his or her nose has been taken away. Someone, usually an adult, grabs at the child's nose and forms the fig sign, exclaiming, "I've got your nose, I've got your nose!" The thumb is supposed to be the child's removed nose.

Many [[neopaganism|neopagans]] use this gesture as a symbol of the [[mother goddess]] to help adherents identify one another. In this context, it is referred to as the "Sign of the Goddess". Its counterpart is the ''[[corna]]'' sign.

In [[The Gnostic Mass]] of [[Aleister Crowley]], this gesture is assumed by the priest throughout the Mass when his lance is not in his hand. It is a phallic device and symbolizes copulation, the fruit of which is a fig, traditionally appropriated to Jupiter the phallic sky god. The use of "the ficus" in the Gnostic Mass replaces the sign of benediction (mentioned above) used in Christian ceremonies.

===Finger Snap===
{{Unreferenced|date=September 2006}}
One of several gestures familiar to modern people primarily through old [[animated cartoons]], this gesture generally expresses a confident "screw you!" in the face of an adversary. The gesturer holds one hand out, palm up, in the direction of his antagonist and snaps his thumb and middle finger, generally accompanied by a high-nosed, "snooty" facial expression and followed by crossing the arms.

In some countries, particularly Great Britain, snapping the fingers is used to signify remembering or failing to remember. Snapping the fingers repeatedly at a constant rate is commonly used to signify that the person has forgotten something and is trying to recall it. This is often done with the fingers snapped close to the temple, as though literally 'jogging the memory,' and is associated with the phrase 'it's on the tip of my tongue.'

A single snap, sometimes emphasized by an arced swing of the arm, is used when someone is reminded of something by another person, particularly if it is a job or a chore they have forgotten to do, or as a sign of disappointment or regret. Some people also snap their fingers to catch the attention of others. This is informal - some people may find it rude or even threatening, as it is common for the gesturer to snap his fingers very close to the other's face. In some cases, this may be interpreted as a face-threatening act or a sign of contempt.

==="Hanging"===
This gesture is performed by holding a clenched fist at the side of the head, tilting one's head away from one's fist, and making a choking sound. It may also be accompanied by hanging the tongue loosely out of one's mouth, and rolling of the eyes back into the head. It is generally used to signify "what I would rather be doing". It can also be used to show suicide.

===Horns===
{{main|Corna}}
[[Image:gesture raised fist with index and pinky lifted.jpg|thumb|right|200px|Corna]]

Many [[neopaganism|neopagans]] use it as a symbol of the [[horned god]] to identify each other; in this context it is referred to as the "Sign of the Horned God". Its counterpart is the ''fig sign'', above.

Some say that it is meant to ward off — or to bestow — the [[evil eye]]. It is also a representation of the [[Devil]] by some [[Satanist]]s. The gesture's origin is believed to be an imitation of the shape of a goats head, which has many associations with the concept of Satan in [[Christianity]] [http://www.keyway.ca/htm2001/20010924.htm Satan's Goat]

It has a variety of other meanings as well, depending on culture and area. In some places, it is a sexual insult, charging a man with being a victim of [[adultery|cuckoldry]] (this insult is most common in [[Spain]] and [[Italy]] but is also used in Brazil). Perhaps because of its [[occult]] significance, it is used as a salute by fans of [[Devil horns#Heavy metal|heavy metal music]]. If one reverses the extended fingers, one gets the "inverted heavy metal salute" which can be given as a reply to a heavy metal salute. In this case, the sign is known as "devil horns".

Also a common hand gesture used by the University of Texas at Austin. The sign is also usually accompanied by the slogan "Hook 'Em Horns." The gesture is said to look like a head of a Longhorn, the University's mascot.
To [[Chaote]]s practicing [[Lovecraftian magick]], it is called the "Sign of Voor" or the "Voorish Sign".

===Kodály Hand Signs===
Named after [[Zoltán Kodály]], and largely defined by [[John Curwen]], Kodály Hand Signs are a way of representing musical notes by holding the hand in a certain position for each note. The basic concept of using gestures to represent notes is quite ancient, however near the end of the 19th century, the concept was formalized as a standard teaching method. Kodály Hand Signs are featured in the [[1977]] film [[Close Encounters of the Third Kind]].

===Knocking on wood===
{{main|touch wood}}
This signifies the neutralization of a [[jinx]]ing brought on by mentioning an either hoped-for or feared result. The knuckles are rapped on a nearby piece of wood (or, jokingly, someone's head). Usually this is only valid if done on bare (i.e. unpainted) wood. One possible reason for the tradition could have been from an [[animist]] culture who believed that the knocking would release spirits to protect them. It has also been said to stem from a belief that any nearby evil spirits who overhear somebody speaking of good fortune which has come his way may send some bad luck to offset it; knocking on wood was thought to keep the spirits from hearing. It is also known as "tapping wood" or "touching wood".

In Italy, one knocks on iron with the hand in the ''[[corna]]'' horns position.

===Middle finger===
{{main|The finger}}
[[Image:Middle finger.JPG|thumb|right|200px|"[[The finger]]" is a very common offensive hand gesture.]]
"The finger" is a gesture consisting of a fist with the middle finger extended. It appears to be universally understood as "[[fuck|fuck you]]"or get stuffed due to its resemblance to the penis. It is certainly thousands of years old, being referred to in Ancient Roman literature as the ''digitus infamis'' or ''digitus impudicus''. Performing this gesture is also called "flipping the bird" in countries where "the finger" is used. In other regions, "flipping the bird" refers to the raising of the middle and index finger with the back of the hand directed at the recipient. It can also mean "Victor" (see ''[[#V Sign|V Sign]]'', below) in some countries, which is not to be mistaken for the "Peace" gesture, which is done with the palm facing the recipient of the gesture, but in Britain and some other countries it is an offensive gesture, equivalent to "the finger". [[George W. Bush]] can be seen making the gesture while he was the Governor of Texas, while goofing off before beginning filming of a public address.<ref>[http://www.youtube.com/watch?v=o9Do-s1cdPk Bush "One-fingered Victory Salute" Video] </ref>

Former [[professional wrestler]] [[Stone Cold Steve Austin]] used the finger quite frequently in [[World Wrestling Entertainment|WWE]] shows. He raises both of the fingers to the crowd as a way of saluting to them. Also, he gestures the finger at his opponent before kicking them in the stomach and performing the [[Stone Cold Stunner]].

Comedian [[Dane Cook]] parodied the gesture with his "Super Finger" gesture, which consists of raising the middle finger, ring finger, and thumb on the same hand while lowering (or curling) the pointer and pinky finger. It is meant to be a more "powerful" version of "the finger".

The middle finger is also used to represent the number four when one counts in the binary system using one's fingers.<ref>[http://www.intuitor.com/counting/]</ref>

When this gesture is made with the palm facing forward, it is known to [[Chaote]]s practicing [[Lovecraftian magick]] as the "Sign of Kish". Another Lovecraftian sign is the "Sign of Koth", which consists of fully extending the index finger, middle finger, ring finger, and pinky, while the thumb is tucked against the flat of the hand.

=== Money sign ===
The thumb rubs repeatedly over the tip of the index finger and middle fingers. The ring finger and pinky touch the palm. This gesture is meant to resemble the act of rubbing two coins together (alternatively the act of counting paper bills) and has a general meaning of "money", or "expensive".

===OK===
{{main|Okay}}

This is the touching of the index and middle finger (or just index finger) with the thumb (forming a rough circle) with the raising of the remaining fingers. In the United States and most of Europe, it means "OK" and is inoffensive. The OK sign is used extensively in [[scuba diving]]. It can also mean "[[0 (number)|0]]," or "[[money]]," in [[Japan]].
However, in Germany, it is often seen on the Autobahn, as a silent way of calling someone an "Asshole" (with the fingers extended horizontally). Similar vulgar meanings are found in other countries, but usually you have to turn the 'Ring' upside down (supinated to show the ring in front) like this example from [http://jeroenarendsen.nl/2006/05/butthole-is-not-ok.html Brazil]. It is then a sexual or scatological gesture referring to the [[anus]]

===Moutza (Palm of hand)===
{{main|Moutza}}
In most places, a palm raised towards somebody means "stop".

In [[Greece]], the palm of the hand thrust towards somebody with the fingers splayed is an offensive gesture equivalent to giving the finger. The gesture is known in Greek as "moutza". It originates from the Byzantine punishment of parading a chained criminal around town with his face smeared with [[cinder]], or ''moutzos'' in Greek. An even more offensive version is achieved by using both hands to double the gesture, and smacking the palm of one hand against the back of the other, in the direction of the intended recipient. Both the one-handed and the two-handed versions of this gesture can be (and often are) combined with the term "''na''!", meaning "here you go!" or "there!", or "''na, malaka''!", meaning "there, you wanker!"

===Salute===
{{main|Salute}}
There are many forms of [[salute]] gestures, most of which are used to denote respect or obedience for an authority. A common [[military]] hand salute consists of raising the right hand, held flat, to the right eyebrow. [[Scouting]] organizations use related salutes. The armies of various countries adopt slightly different forms of salute: in the United States, the military salute places the hand directed outward over the eyebrow, like a visor; in the United Kingdom armed forces, the hand is brought to the forehead palm outward in military and air force contexts, whereas the naval salute is as in the US forces - the US forces derived their saluting habits from the [[Royal Navy]].

One of the most infamous forms of salute is the "[[Hitler salute]]", which is performed by extending the whole right arm, palm outstretched and facing down, upwards into the air at approximately a 45 degree angle from the ground. Sometimes, this is accompanied by holding the index and middle fingers under the nose, representing Hitler's iconic moustache. This gesture is associated with [[Nazism]] and its leader, [[Adolf Hitler]], as well as with [[Germany]] during [[World War II]]. It is occasionally performed to mock someone or something for perceived [[authoritarianism]] or [[bigotry]]. This gesture was based on the [[Roman salute]], and it was in that capacity that it was revived by [[Tennis Court Oath|French Revolutionaries]] and later by [[Benito Mussolini]]'s [[Fascism|Fascist]] party.

In some countries, mostly in Europe, it is forbidden by law to perform this gesture, although this does not deter [[Neo-Nazism|Neo-Nazis]] and white supremacists from using the gesture in public rallies. Even in other countries, it is generally considered taboo to use the gesture, and this partly caused the [[United States]] to abandon the similar [[Bellamy salute]] used when reciting the [[Pledge of Allegiance]], in favor of the current hand-on-heart gesture.

===Shaka===
{{main|Shaka sign}}
[[Image:gesture raised fist with thumb and pinky lifted.jpg|thumb|right|200px|The "[[shaka sign|shaka]]" sign is a common greeting in beach and surfer culture.]]

The "shaka" sign is a common greeting gesture often associated with [[Hawaii]], [[California]], and [[beach]] and [[surfing|surfer]] culture in general. It consists of extending the thumb and pinky finger while keeping the three middle fingers curled, and is often described colloquially as the "hang loose"or "chilax" gesture. It is similar to [[American Sign Language]] letter "''Y''", where a fist is also made with only the thumb and pinky extended. The sign is often followed by waving as a greeting or acknowledgment. It can be used when driving as a signal of thanks to other drivers (for example, someone who stopped to let another driver onto the road from a driveway).

The "shaka" sign is also the greeting gesture for members of [[Alpha Phi Alpha]] Fraternity, Inc. which is the "phi" sign. All African-American Greek fraternities and sororities have hand greeting gestures.
====Similar gestures====

In Britain and Northern Europe the symbol is used as a signal for owners of older model [[Volkswagen]] vans when passing on roads. The silhouette of the hand reveals a "W"-shaped outline along the top of the hand standing for Volkswagen.

In Spain and Italy, if the thumb points to the mouth, it means "drinking", since it is similar the shape of a ''[[porrón]]'' vessel. This is also true of the [[United States]], [[Portugal]] and [[Brazil]].

In some countries, if the thumb points to the mouth, it can also represent [[marijuana]] usage, in particular the use of a [[bong]]. This is usually accompanied by a sucking noise.

In China, it is also the sign for the number six.

A similar gesture is the "call me" sign, which also has the pinky finger and thumb outstretched, but then also holds it up to the ear, to signify a telephone. This gesture is a common way to silently tell someone to call him or her, such as to continue a conversation in private.

It is also used by [[FC Barcelona]] player [[Ronaldinho]] as part of his goal celebration.

In India, rolling the shaka in a winding motion signifies that the listener does not believe what is being said and that the speaker needs to "spool in the yarn from spinning out too far".

In [[American Sign Language]], a "rolling" version of this sign indicates the activity "play", often used by non-verbal (i.e. pre-speech children) people to ask if one wants to play or that they signer wishes to play.

==="Thanks!" Salute===
Another gesture familiar from vintage cartoons, this is performed by sweeping an opened hand from near one's brow toward the person being addressed, and expresses gratitude. It is adapted from [[American Sign Language]], and alludes to tipping your hat or cap.

===Three middle fingers===
Gestures consisting of fully extending the index, middle, and ring fingers with the thumb and pinky tucked together under the palm have had a variety of meanings over the years.

The gesture was also used by [[Bosnian Croat]]s as a victory sign, representing the Christian [[Trinity]], during the [[Bosnian War]]. To [[Chaote]]s practicing [[Lovecraftian magick]], this gesture is known as the "Sign of the Elders." With the palm facing outwards, the fingers closed (without gaps), the right hand's fingertips to the same-side temple, it is used by the [[scouting|Boy scouts]] as their identifying [[salute]].

In the United States, when the back of the hand faces outwards, this gesture is often used as a [[euphemism]] for "[[#middle finger|the finger]]." It is used especially when a jocular effect is desired. Originally, an accompanying verbal explanation was usual — "Read [[subtext|between the lines]]," referring to the common English expression denoting that one must read carefully to glean the subtle meaning in a passage — but this phrase is now commonly omitted.

===Thumbs up, thumbs down===

A closed fist held with the thumb extended upward or downward is a gesture of approval or disapproval respectively. These gestures have become metaphors in English: ''"My boss gave my proposal the thumbs-up"'' means that the boss approved the proposal, regardless of whether the gesture was made — indeed, the gesture itself is unlikely in a business setting.

The source of the gesture is obscure. Though a favorite of Hollywood '[[sword and sandal|swords and sandals]]' epics, where the "thumbs down" symbol means that the loser in a gladiatorial combat should be put to death, recent research suggests the meanings of the symbols have changed over the years. In [[1997]], Professor [[Anthony Philip Corbeill]] of the [[University of Kansas]] concluded that the thumbs up actually meant "Kill him," basing his assertion on a study of hundreds of ancient artworks. Thus, the "thumbs up" was an approval of the gladiator's request to kill his vanquished foe rather than a vote to allow the defeated to remain alive. Corbeill wrote that a closed fist with a wraparound thumb was the indication for a gladiator's life to be spared.

[[Image:Jean-Leon Gerome Pollice Verso.jpg|thumb|right|200px|''Pollice Verso'' by Jean-Léon Gérôme, [[1872]] is the immediate source of the "thumbs down" gesture in [[popular culture]].]]

In [[Latin]], the "thumbs up" gesture is called ''pollice recto'', "thumbs down" is ''pollice verso''. It is not certain that the contemporary gestures are identical to the gestures performed in [[ancient Rome]]. The current version was popularized by a widely reproduced [[academic art|academic painting]] by the [[19th century]] artist [[Jean-Léon Gérôme]], whose ''Pollice Verso'' depicts a triumphant gladiator standing over a fallen foe, looking up into the [[bleacher]]s for the verdict of the crowd.

Additionally, [[Desmond Morris]]' ''Gestures: Their Origins and Distribution'' traces the practice back to a [[medieval]] custom used to seal business transactions... Over time, the mere sight of an upraised thumb came to symbolize harmony and kind feelings... The gesture's popularization in America is generally attributed to the practices of World War II pilots, who used the thumbs up to communicate with ground crews prior to take-off. American GIs are reputed to have picked up on the thumb and spread it throughout Europe as they marched toward Berlin." [http://slate.msn.com/id/2080812/]

More recently, these gestures are associated with [[film|movie]] [[review]]s, having been popularized by [[Gene Siskel]] and [[Roger Ebert]] in their televised reviews — the thumb up meaning a positive opinion of a film; the thumb down meaning a negative one. One or two thumbs up, often held over the head, may also be used by athletes in celebration of a victory.

"'Thumbs up' traditionally translates as the foulest of Middle-Eastern gesticular insults — the most straightforward interpretation is 'Up yours, pal!' The sign has a similarly pejorative meaning in parts of West Africa, South America, Russia, Iran, Greece, and Sardinia, according to Roger E. Axtell's book ''Gestures: The Do's and Taboos of Body Language Around the World''."[http://slate.msn.com/id/2080812/]

[[Hitchhiker]]s traditionally use a thumbs up gesture to solicit rides from oncoming vehicles, although in this presentation the arm is generally outstretched with the palm and closed fingers facing the motorist. People who have the genetic ability to bend the tip of their thumb backwards are said to have "hitchhiker's thumb," which is a reference to the original gesture.

Additionally, supporters of [[Texas A&M University]] athletic teams use the thumbs-up sign, associated with the cheer, "Gig 'em, Aggies." The Thumb refers to a "gig" used for hunting frogs. The saying came when the Aggies had a big rival in the Southwest Conference in the TCU Horned Frogs.

Thumbs up and thumbs down are extensively used in scuba diving as commands to ascend or descend.

[[World Wrestling Entertainment|WWE]] Superstar [[Dave Bautista|Batista]] uses this gesture to signify his finisher, the [[Batista Bomb]].

=== Tsk-tsk ===
Palm towards the recipient, all fingers closed except for the index, which alternates from left to right, like a [[metronome]]. In English-speaking countries it has a disapproving meaning and can be accompanied by a "[[tsk|tsk-tsk]]" sound. This is also known as "finger-wagging".

In Italy and Brazil it simply means "no", and does not have any patronizing connotation.

===V sign===
[[Image:Nixon-depart.png|thumb|right|200px|[[Richard Nixon]] gives the V-sign one last time after resigning from the presidency.]]
{{main|V sign}}

The "V sign" is made by lifting the middle and index finger with the palm of the hand facing the recipient (and the remaining fingers clenched). It was associated with the [[catchphrase]] ''"V" for Victory'' in [[World War II]]. In the [[1960s]], it came to be known as the "[[peace]] sign," the gestural equivalent of the [[peace symbol]]. It was associated with British prime minister [[Winston Churchill]] during World War II, and later, with U.S. president [[Richard Nixon]]. It is also the sign for the letter V in [[American Sign Language]].

This sign is frequently used by the Japanese, most times holding up 2 "V" signs very close to either side of their face with a big grin during pictures.

In the UK, Australia, and some other countries, reversing the V sign so that the back of the hand facing the recipient is seen as the equivalent of giving [[finger (gesture)|the finger]]. Popular myth supposes it was originally a taunt by English Longbow Archers towards the French who were known to cut off an English Archer's first and middle fingers if captured.

Additionally, due to its use in an advertisement for the Australian made Valiant Charger (which ceased production around 1980) many people still display the V sign, in homage to the ad, and the car, if that vehicle happens to be driven past. Hardly an every day occurrence, but of some trivial interest.

===Vulcan salute===
{{main|Vulcan salute}}

The Vulcan salute consists of a raised hand, palm outward, fingers extended, with the index and middle finger kept close together, and the ring and pinky finger close together, with a "V" shaped space between them, and the thumb sticking out alone.

This gesture is associated with the phrase "Live long and prosper", and derives from ''[[Star Trek]]'', where it is used as a salute by fictional humanoid species the [[Vulcan (Star Trek)|Vulcans]].

It was introduced by [[Leonard Nimoy]] in his character of [[Mr. Spock]] and is drawn directly from the benedictory gesture made with both hands by a [[Kohen]] (priest in Judaism, a descendant of Aaron) during the [[Priestly Blessing]] ([[Hebrew language|Hebrew]]: ''Birkat Kohanim''). The [[Kohen|Kohanim]] recite a blessing while performing this "gesture" and the other congregants respond with [[Amen]]s.

This gesture is also known as the "Spocker" in allusion to [[Shocker (hand gesture)|the Shocker]].

===Wanker===
[[Image:Fingers and thumb in circle downward motion.jpg|thumb|right|200px|Wanker]]
A loose fist (with all fingers forming a cylindrical shape) is made, and shaken up and down (or sometimes, back and forth) at the wrist.

The gesture is imitative of the motions of male [[masturbation]]. Its meaning is equivalent to the word [[wanker]] or implies something is of little importance. If directed to a person or group, who are not necessarily present, it is considered a display of contempt toward them.

The name for this gesture is described by speakers of [[American English]] as a [[Britishism]].

[[Image:Portugal Wanker Gesture.jpg|thumb|right|200px|The Overhand Portuguese Wanker Gesture]]

In [[Portugal]] they use the wanker gesture but with the palm facing the ground thereby implying that the person is masturbating someone else rather than themselves. As such this has [[homosexual]] or promiscuous implications when directed at someone instead of the milder suggestion that they enjoy self-gratification.

In the United States, this gesture can indicate contempt, particularly indicating that the gesturer thinks something is a waste of time.

===Wave===
A wave is a gesture in which the hand is raised and moved back and forth, as a [[greeting]] or sign of departure. The orientation of the hand varies by culture and situation. In many cultures, the palm is oriented toward the recipient of the wave.

In Chinese culture, orienting the hand palm-down and waving it up and down signifies "come here", rather than a greeting. 

===Whoop-Dee-Doo===
Point the index finger up and rotate it. This simulates the waving of a tiny, sarcastic flag and is a usually used as a response gesture to indicate something is uninteresting or irrelavent. Similar to saying a sarcastic "Whoop-Dee-Doo" or "Big deal".

==Using two hands==
{{main|Hand gesture}}
===Awkward Turtle===
The Awkward Turtle is a gesture made after something awkward just happened, or when there is an awkward silence.
To perform an awkward turtle there are three steps to take. First, place hands on top of each other. Next, move thumbs out and away from the hands. Finally, rotate the thumbs.

Nowadays the gesture is used in the United States to hush children, or to calm participants in a heated argument. In [[Japan]], the same gesture may be used to request the check when dining at a restaurant (see also [[#Check, please|Check, please]], above).

==="Gills"===
This gesture involves holding the backs of the wrists against the jawline (with elbows outstretched) and then waggling one's fingers. The gesture is often accompanied by a feminine-voiced "Ooooo!" which rises and falls in intonation. It is used when one would normally say (sarcastically) "well aren't you clever?", or to imply that someone is acting too posh for their station. It is peculiar to Scotland owing to its use in Scottish TV sketch show [[Chewin the Fat]].

==="Shame on you"===
This gesture involves pointing at a person with the index finger of one hand while rubbing the pointed finger with the index finger of the opposite hand. The rubbing motion is directed toward the intended recipient and is repeated at least three times. It is used to imply that the targeted person should feel shame.

===Time-out===
The "time-out" gesture — a "T" formed with the hands, with one hand with flat palm placed perpendicular to the other hand with flat palm, roughly in the center — originates in American sports. It was, and is, used where a brief [[sport time-out|pause in play]] is called for, such as to make substitutions. In [[basketball]], the gesture is used to indicate that a player or coach is guilty of a [[technical foul]].

===Whatever!===
A gesture associated with [[Valley Girl]]s. Forming the letter "W" by extending the two index fingers upward and touching the thumbs together at a 45 degree angle, this hand sign is used silently or in conjunction with an uttered "Whatever!" (pronounced with a slight pause after the first syllable, emphasis on the second, and drawing out the third syllable to a hard "r"). It is a sarcastic response dismissing whatever has just been said to the person making the gesture.

==Hand with body gestures==
{{Mergeto|Hand gestures|Talk page|date=April 2007}}
===Bent elbow===

This is performed in two parts: first, the right hand is placed in the elbow crook of the left arm. The left arm is then raised (fist clenched) at the victim in a smooth and continuous motion. While the motion is essential to the gesture, the choice of arm is not. This gesture is associated with [[Italy|Italians]] and is considered a more theatrical and physically exuberant version of the [[finger (gesture)|finger]], and may even be combined with the finger. In Italian it is known as the ''gesto dell'ombrello'', meaning literally "the umbrella gesture." It is typically used in two different situations: 1) to answer "no way!" in an extremely emphatic (and quite vulgar) way; 2) after a triumph against some unfair enemy, with a sense of revenge. The gesture is frequently made stronger by crying "toh!" or "tiè!", both meaning "take this!", at the precise moment the hand touches the crook of the elbow.

This gesture is also in use in [[France]] as ''bras d'honneur'' (arm of honour), where it is usually understood as ''va te faire foutre'', still meaning "fuck off." In [[Spain]] and [[Portugal]], it is a ''corte de mangas'' ("[[sleeve]] cut") or a ''manguito'' (a cover formerly worn by public services bureaucratic workers on the arms to protect one's sleeves from ink splatters) respectively and is done with the left hand on the right elbow, without the continuous motion. In [[Portugal]], the iconic fictional character [[Zé Povinho]], created by [[Bordalo Pinheiro]], is usually depicted performing this gesture. This gesture, known as ''banana'', was also once used in Brazil with the meaning of "fuck you", but it has not been used since the middle of the 90's.

The gesture is sometimes used repetitively by fans at [[Citizens Bank Park]] in [[Philadelphia]] when the [[Phillies]] face the [[Atlanta Braves]] as a [[parody]] of the Braves' [[tomahawk chop]], and this usage is known as the "[[South Philly]] tomahawk chop" due to the gritty reputation of [[Philadelphia]] sports fans.

The gesture above has long been known in Slavic countries and Greece in the above senses plus "fuck you", without any standard name. In [[Poland]] its name has been standardized to "Kozakiewicz's gesture", after Polish [[pole vault]] jumper [[Władysław Kozakiewicz]], who had shown this gesture to the jeering Russian public during the [[1980 Summer Olympics]] in [[Moscow]].

===Biting one's thumb===


[[Biting one's thumb]] was an old rude British gesture. It is comparable to "[[#middle finger|the Finger]]" in modern terms. In [[William Shakespeare]]'s play ''[[Romeo and Juliet]]'', Sampson bites his thumb at the Montagues (Act 1, Scene 1).

The gesture does not literally involve biting the thumb. The fingernail of a thumb is placed behind the upper teeth, with the thumb thus pointing upwards, and the thumb is then bent forwards, the fingernail making a clicking sound as it flicks past the teeth.

An equivalent gesture still persists in [[Italy]].

=== Biting one's hand ===
In Sicily, biting one's flat hand or fist is a powerful threat.

===Bowing, kneeling, kowtowing===
A [[bowing (social)|bow]] is a gesture of respect involving lowering the head, usually performed by a social inferior to a social superior. Various cultures have different degrees or ways of performing the bow; [[China]] and [[Japan]] are particularly associated with elaborate and formal bowing. Bowing is also done by many groups as a ritual associated with [[prayer]]. In the Western world, women [[curtsey]] rather than bow. [[Kneel]]ing and "[[kowtow]]ing" are more extreme or elaborate forms of self-abasement before a social superior.

===Choking sign===
[[Image:Chokinggesture.JPG|200px|thumb|right|The "Choking" sign]]
The standard gesture to indicate that one is [[choking]] is to hold the throat with both hands as if strangling oneself. This is recognized as a request for immediate [[first aid]] for choking. It is promoted as a way to prevent onlookers from confusing the victim's distress with some other problem, such as a [[myocardial infarction|heart attack]], when the person cannot speak. The gesture is sometimes used metaphorically to refer to someone or something "choking" in the slang sense of failing at something while under pressure, for instance at an athletic event.

===Crossing oneself===
{{main|Sign of the cross}}
The "[[sign of the cross|sign of the Cross]]" is the use of the right hand to touch the forehead, chest, left shoulder, and right shoulder, consecutively. It represents the [[Christian cross]]. (Roman Catholics crossing themselves touch the forehead, chest, left shoulder, then right shoulder; Byzantine (Eastern) Catholics and Eastern Orthodox Christians touch the right shoulder before the left, with the thumb and first two fingers joined — symbolizing the Trinity — and the tips of the last two fingers touching the palm, symbolizing the dual nature of Christ in one being. )

This gesture is used by [[Roman Catholic]]s, [[Eastern Orthodox Church|Orthodox Christians]], and some other Christian groups in [[prayer]]s, to perform blessings, and as a salute before entering a [[church]] or similar place of religious significance. It is also used in various kinds of Christian [[folk religion]] to avert [[evil]] or [[bad luck]].

===Cutthroat===
[[Image:Cutthroatgesture.JPG|200px|thumb|right|The "Cutthroat" sign]]
This gesture is performed by drawing the hand, or a finger or two, across the throat. It represents slitting the throat with a knife, and means that the gesturer or someone else is metaphorically being killed. It is rarely if ever used literally to refer to death, though it is occasionally used as a theatrical threat ("I'm going to kill you"). In these contexts, it is sometimes accompanied by a harsh "kkkkkch" sound.

This gesture can also mean to "cut," "stop," or to discontinue a particular action. It can also be used to indicate something has ended or a previous process has concluded. [[Scuba diving|Scuba]] divers use this gesture with the palm swept across the throat to indicate that they have run out of air. Airport ground personnel also use this gesture to indicate a variety of things (due to the loud environment), such as baggage offload has completed or the last of the passengers have disembarked. In this context, it can be understood to mean: "That's it."

Also used by movie personnel when having to signal a cessation of activity under silent conditions.

Additionally, [[World Wrestling Entertainment|WWE]] Superstar [[The Undertaker]] uses this gesture to signify his signature moves, the [[Chokeslam]], [[Powerbomb#Elevated powerbomb|Last Ride]], and [[Piledriver (professional wrestling)#Tombstone piledriver|Tombstone piledriver]], as did [[Chris Benoit]] until his recent death.

=== Drinking sign ===
In UK, the gesture for drinking (used for example as an invitation to "go down the [[pub]]") is made by putting the back of the thumb just below the lower lip, while the other fingers are close together as if holding an imaginary [[pint]] of beer, tipping it repeatedly. This gesture can also be used to imply that somebody is drunk, either literally or insultingly.
In other countries, the shaka sign is used in a similar way, as described above.

===Flipping the fingers out from under the chin===

A [http://news.bostonherald.com/localRegional/view.bg?articleid=132932 traditional Sicilian gesture] analogous in meaning to the raised middle finger. This gesture became the center of a controversy in March of 2006, when [[U.S. Supreme Court|Supreme Court]] [[Associate Justice]] [[Antonin Scalia]] was photographed allegedly making the gesture to illustrate his response to his critics. Scalia later claimed that he used a different gesture, waving his fingers beneath his chin, a gesture translating to "I couldn't care less."
===Forehead Clunk===
This gesture indicates stupidity, usually a minor and immediately recognized slip of logic, judgment, or speech; and is performed by striking the forehead with the heel of the hand.

=== Hand over heart ===
This gesture involves placing one's right hand, palm outstretched and facing in, over one's heart. Male [[hat]] or cap wearers typically remove their hats and hold them in this hand. In some cultures, it is used as a gesture of respect towards [[flag]]s or during singing of a [[national anthem]]. In the United States, it is also performed as a part of the rituals of the [[Pledge of Allegiance]]. It can also be used to indicate sincerity, shock, or hurt; in which case, a balled hand has the same meaning.

===Loser===
This gesture is performed by raising the index finger and thumb of your right hand perpendicular to each other so that they form the letter "L". It is then placed onto one's forehead. It signifies that the person to whom this gesture is directed is a loser.
However, when the opposite hand is used, the gesture becomes highly ironic.

===My eye===

In France, Germany, and other parts of Europe{{Fact|date=September 2007}} it is common to point your index finger at your eye and even pull the skin under the eye lightly down to emphasize the presenting of the eye. The gesture displays disbelief or that a certain statement is made jokingly, similar to winking in American culture.

In Japan, tugging at the eye, often accompanied by sticking out one's tongue, is used as a childishly offensive gesture, or to indicate boredom.

In Italy, Portugal, Brazil and all Spanish-speaking nations it means "watch out" (POR, ITA:''occhio!'',SPA:''¡ojo!''), and is used for warning or threatening.

In Denmark it can be a joking threat, often accompanied by the phrase: "Because the eyes are what you takes care for the most".

===Nonsense===
Performed by waving the palm of your hand in front of your face, it may be used to tell the other person that an idea he or she had was nonsense.

In [[Portugal]], this gesture usually means the person being referred to missed an extremely obvious detail.

===Nose thumbing ===
For this gesture, also known as "cocking a snoot", "giving the five-finger salute", "cocking a snook", or Queen Anne's Fan, the thumb is placed on the tip of the nose, with the remaining fingers of the hand extended and waggled freely. This gesture can be ended with a dramatic flicking of the thumb away from the end of the nose and towards the recipient. It is used in (gentle) mockery of someone. It dates back to at least the 18th century and is probably much older.

To add emphasis, the gesture can be made using both hands, connecting them by touching the little finger of the first hand with the thumb of the second, and waggling the remaining seven fingers. It is frequently accompanied by [[blowing a raspberry]], or by sticking out the tongue.

===Over the Head===
A hand is extended and passed over the head with the palm facing the head. This is often accompanied with a whooshing sound or an exclamation of "Over your head!". This indicates that the receiver has failed to comprehend or notice something obvious.

===Screwing The Forehead===
A finger is placed against the temple, as if pointing at it, and a screwing motion, as if making a dimple, is made by twisting the wrist. In Italian culture, this indicates that the person referred to is "crazy" or "nuts."

===Suck my dick===
This gesture is performed by crossing the outstretched arms across the thighs, putting emphasis on the [[groin]]. This was used by popular professional wrestling [[stable (wrestling)|stable]], [[D-Generation X]].

There is a variation to this where a fist is made and shook near the mouth while bulging ones tongue against their cheeks to mimic fellatio.

===The Turkish Fig===
In [[Turkey]] and [[Greece]], putting the thumb between the middle and index finger of the right hand and making a fist is called "the fig" and is extremely offensive. In Turkey, taking that fist, placing it in the left hand and then pushing it out to make a slapping sound with the wrist of the right hand is even more offensive, and is usually accompanied by a string of obscenities. These gestures are often seen at soccer games.

===Touched / screw loose===
Tapping one's index finger against the head indicates that a person or an idea being discussed is insane or "touched in the head". A similar, more elaborate gesture uses a circling motion of the finger at the temple or side of the head. This signifies that the person is "mixed up" or "has a screw loose". In Germany, tapping or pointing to the temple is used as an insult, often with the accompanying phrase "du hast einen Vogel." While this literally means "You have a bird," it is idiomatic for saying that you are insane. Also, in Indonesia, drawing a line across the forehead with the side of the right index finger denotes a similar meaning.

A variant of this one is the suicide. Make a gun with your hand and pretend to shoot point blank at your own temple. It can be accompanied with sticking out the tongue or a shooting sound for full effect, and often implies that the speaker is a "complete idiot". A more recent use of this is in the movie, "40-Year Old Virgin" where one of the characters, after being bored with a conversation, proceeds to aim at his temple and pretend to fire. Afterwards, he uses his other hand and does a reverse cupping motion outward from the other side of his head to signify his brains splattering out.

In Japan, a variation of this is knocking on the temple with the knuckle of the index finger. This is usually used in reference to the signer; "I'm such an idiot!"

===Twisting The Cheek===
Thumb and forefinger are placed against the cheek, and a screwing motion, as if making a dimple, is made by twisting the wrist. In Italian culture, this can mean "I see a pretty girl" or, just generally mean "Wow!"

==="Wiping" one's forehead===
The act of wiping one's own forehead, regardless of whether sweat has actually formed there, is a sign indicating many things such as "That was close" or "What a relief". It can also be used to express relief after some hard work, or to express feeling hot.

==Body and facial gestures==
{{further|[[Facial expression]]}}
[[Image:Eyeroll.JPG|thumb|right|200px|Rolling one's eyes can express exasperation or condescension.]]

Many gestures utilize only the face or body, without the hands.

===Eye-rolling===
Performed by rotating the eyes upward, it indicates condescension, contempt, boredom, or exasperation. This is often referred to as "rolling ones eyes to Heaven," as though wishing for a divine intervention for a rescue from boredom, frustration, etc.

===Mooning===
[[Mooning]] is the act of displaying one's [[nudity|bare]] [[buttocks]] by lowering the back side of one's [[trousers]] and [[underpants]], usually without exposing the [[genitals]]. Mooning is used in some cultures to express protest, scorn, disrespect, or provocation. It can also be done for [[shock value]] or fun.

===The "peacock"===
Expresses superiority or domination combined with a certain degree of smug arrogance. Performed by pushing the chest up and out at the front as well as tilting the face slightly upward. This may be accompanied by motions of hooking both thumbs under one's [[lapels]] or [[suspenders]] even if they are not present.

{{Gestures}}

==References==
{{reflist}}

[[Category:Gestures]]

Archive:Types of gestures

2007-11-30T04:20:41Z

24.113.30.224:

{{unreferenced||article|date=September 2006}}
Gestures are a form of [[Body language]] or [[Non-verbal communication]].
Although some [[gesture]]s, such as the ubiquitous act of [[Hand gesture|pointing]], differ little from one place to another, most gestures do not have invariable or universal meanings, having specific connotations only in certain cultures. Different types of gestures are distinguished. The most famous type of gestures are the so-called emblems or quotable gestures (see the examples below). These are [[culture]] specific gestures that can be used as replacement for words. Communities have repertoires of such gestures. A single emblematic gesture can have very different significance in different cultural contexts, ranging from complimentary to highly offensive.

Another type of gestures are the ones we use when we speak. These gestures are closely coordinated with speech. The meaningful part of the gesture is temporally synchronised with the co-expressive words. For example, a gesture that depicts the act of throwing will be synchronous with the word 'threw' in the utterance "and then he threw the ball right into the window." Other gestures like the so-called beat gestures, are used in conjunction with speech, keeping time with the rhythm of speech and to emphasize certain words or phrases. These types of gestures are integrally connected to speech and thought processes.

==Studies of gesture==
The first full-length study of gesture was published by [[John Bulwer]] in 1644. Bulwer analyzed dozens of gestures, and provided a guide on how to use gestures to increase eloquence and clarity for public speaking. Today, one of the most prominent researchers in the field of gesture research is [[Adam Kendon]]. He has investigated many aspects of gestures, including their role in communication, conventionalization of gesture, integration of gesture and speech, and the evolution of language. Other prominent researchers in this field include [[Susan Goldin-Meadow]] and [[David McNeill]].

==Social significance==
[[Image:VitarkaMudra.JPG|thumb|right|200px|Vitarka [[mudra]], [[Tarim Basin]], 9th century.]]

Gestures play a major role in many aspects of human life. Many animals, including humans, use gestures to initiate a [[Courtship|mating ritual]]. This may include elaborate [[dance]]s and other movements.

Religious and spiritual gestures are also common, such as the [[Christianity|Christian]] [[sign of the cross]]. In [[Hinduism]] and [[Buddhism]], a ''[[mudra]]'' ([[Sanskrit]], meaning either "posture" or "currency" depending on the interpretation) is a symbolic gesture made with the hand or fingers. Each mudra has a specific meaning, playing a central role in Hindu and Buddhist [[iconography]]. An example is the Vitarka mudra, the gesture of discussion and transmission of Buddhist teaching. It is done by joining the tips of the thumb and the index together, while keeping the other fingers straight.

==Using one hand==
{{main|Hand gesture}}
===Itching Under The Chin===
In Italian culture this represents "I don't care, I can't be bothered". This is done by keeping one hand straight, placing it under the chin, and 'throwing out' that hand toward the person receiving the gesture. In Italian American culture this represents "Screw You!"; U.S. Supreme Court justice [[Antonin Scalia]] received criticism for using this gesture towards a reporter.

Scratching or stroking the chin or beard (where possible) can be used to indicate that the gesticulater is thinking or puzzled.
In the UK, an "itchy chin" can be used to indicate that the person receiving the gesture is lying or talking nonsense, [[bullshit]], in other words. In the UK scratching the chin as a way of implying that the speaker is talking nonsense is often accompanied with any or all of the phrases "reck-on", "chinnus magnus" and "jimmy hill" in no particular order.

===Bang bang===
[[Image:gesture thumb up then down forefinger out like gun.jpg|thumb|right|200px|This gesture mimes a [[handgun]].]]

The "bang bang" gesture is performed by raising the fist with the index finger and thumb extended. The index finger points at the recipient. The thumb is then brought down on top of the fingers. This imitation of the action of a revolver [[pistol]] is often meant to represent a [[handgun]] in children's games. It may also be used menacingly to mean "I'm gonna kill you", or simply as a playful greeting. The middle finger is often also extended to widen the "barrel".

[[Texas Tech University|Texas Tech]] fans use the "bang bang" salute (fingers pointed upward) to cheer their team. Also, the "bang bang" performed with both hands was a signature gesture of [[professional wrestling|professional wrestler]] [[Mick Foley]] while he was in his "Cactus Jack" [[gimmick (professional wrestling)|persona]].

Also, if the thumb and middle finger are used to click, and the thumb the pointed upwards to form the gun, this can also be interpreted as a greeting.

A two-handed version of the same gesture can be used to indicate sporting/business success or sexual conquest (frequently accompanied by a syncopated "pow-pow", esp. in a posh British accent).

=== Beckoning sign ===
Index finger sticking out of the clenched fist, palm facing the gesturer. The finger moves repeatedly towards the gesturer (in a hook) as to draw something nearer. It has the general meaning of "come here", although it is normally seen as condescending or anyway impolite. It is sometimes performed with the four fingers, with the entire hand, or even with the arm, depending on how far the recipient of the sign is.

When performed with the index finger, it may have a mild sexual connotation depending on the circumstance.

In [[Africa]], the [[Far East]] and many [[Spanish language|Spanish]]-speaking countries, this sign is given with all four fingers and with the palm down.

In [[Japan]] there is a similar gesture, but the four fingers are used, the palm faces the recipient and the hand is at head's height. This is the gesture featured in the [[maneki neko]].

===Benediction and blessing===
[[Image:ConstantineCoin.jpg|thumb|right|200px|Benediction gesture, on a coin of [[Constantine I (emperor)|Emperor Constantine]].]]

The benediction gesture is a raised right hand with the ring and pinky fingers touching the palm, while the middle and index fingers remain raised. Taken from Ancient Roman iconography for speaking (an example is the Augustus of Prima Porta where the emperor Augustus assumes the pose of an orator in addressing his troops), it is used as a simple [[charm]] or [[blessing]] amongst many [[neopagan|modern]] [[Paganism|Pagans]], and has a vast array of uses. Perhaps the most common and/or noteworthy use of the gesture is while tracing an invisible "air [[pentagram]]" before someone during certain [[Wicca]]n rituals such as the [[Great Rite]] performed during [[Beltane]] and [[Drawing down the Moon (ritual)|Drawing Down the Moon]] on the [[Esbat]]s. One might also use the gesture to trace invisible pentagrams or other sigils over items to be blessed or empowered, such as [[holy water]], [[ritual]] [[wine]], ritual [[ale]], or [[cannabis|the Sacred Herb]]. The two extended fingers are used to point (except when an [[athame]], [[wand]], or [[sword]] is used).

A similar sign, called the ''benediction'' gesture, is used by the [[Christianity|Christian]] [[clergy]] to perform [[blessing]]s with the [[sign of the cross]]; however Christians keep the thumb raised - the three raised fingers (index, middle, and thumb) are frequently allegorically interpreted as representing the three Persons of the [[Holy Trinity]]. It was shown by representations of [[Jesus]] as [[Christ Pantocrator]].

===Blah-blah===
The fingers are kept straight and together in a horizontal fashion while the thumb is held out straight. The fingers and thumb then snap together repeatedly to suggest a mouth talking. It is used to indicate contempt for a person talking for an excessive period of time about nothing the gesturer feels is important.

===Check, please===
This gesture, understood by waiters around the world to mean that a dinner patron wishes to pay the bill and depart, is executed by touching the index finger and thumb together and "writing" a wavy line in the air, as if to sign one's name. An alternate gesture with the same meaning is made by touching the index finger and thumb together and drawing a [[Tick (checkmark)|checkmark]] ({{unicode|<big>✓</big>}}) in the air. In [[Egypt]], the left hand is held palm-out and the right, palm-down, is tapped against the left wrist to request the check. In [[Thailand]], one makes a circling gesture with the thumb and fingers pinched together- as if you are holding an imaginary pencil and making imaginary scribbles on a piece of paper. Sometimes the opposite palm is used as the 'paper'. In the [[Philippines]], one outlines a rectangle in the air using the thumb and forefinger of both hands.

===Clenched fist===
A raised, clenched fist is used as a gesture of defiance by a number of groups. It is usually considered to be hostile, yet without any sexual, scatological, or notionally offensive connotations. It is especially associated with [[Communism|Communists]] and with other nationalist or ethnic [[revolution]]ary or would-be revolutionary movements, and with the [[Black Power]] movements of the [[1960s]] in the United States. It is the custom to make this gesture while singing ''[[The Internationale]]'', the [[Marxism|Marxist]] anthem. A clenched fist raised quickly up and down and then punched in some direction also signifies a military call for a heavy weapons team to close on the gesturer or to move or open fire in the direction indicated by the punch. In US military, a closed right hand fist raised up with a straight arm with the finger side towards the receiver is an order for the person to stop immediately - to "freeze".<ref>[http://www.truthout.org/docs_2006/071007D.shtml Truthout.org]</ref>

: See also: [[With a strong hand and an outstretched arm]]

=== Pound fist ===
Pound fist is a greeting, in which two individuals touch fists.

=== Clinton thumb ===
The gesture dubbed the "Clinton thumb" after its most famous user, [[Bill Clinton]], is used by politicians to provide emphasis in speeches without pointing the finger. This gesture has the thumb leaning against the thumbside portion of the index finger, which is part of a closed fist. It does not exhibit the anger of the clenched fist or pointing finger, and so is thought to be less threatening. This gesture was likely adopted by Clinton from [[John F. Kennedy]], who can be seen using it in many speeches during his political career.{{Fact|date=February 2007}} It is often used in extemporaenous speech and debate, as a tool for emphasizing points.

===Crossed fingers===
{{main|Crossed fingers}}
A gesture made by crossing the index and middle fingers such that the middle finger overlaps and intertwines the index finger, which can be used to signify one's hope that something should succeed (compare to the phrase "Keep your fingers crossed."). According to OldSuperstitions.com, this stems from the [[superstition]] that "Bad luck is trapped at the point where the two fingers meet so when we cross our fingers, we stop the bad luck from escaping and allow our wishes to come true.". However, if placed behind one's back, the gesture takes on an entirely different meaning: it is then normally used to indicate that the user secretly wishes for something ''contrary'' to what is being stated or going on, or that a lie is being told. This usage is often seen in dramatic contexts.

===Cuckoo sign===
A gesture made by closing ones fist, extending the index finger, and circling it around ones ear for several seconds. This gesture is used to indicate that someone is speaking nonsense or is crazy (more colloquially, this is described as being [[cuckoo]]). The "cuckoo" sign is well-known in the United States.

===Fig sign===
[[Image:gesture fist with thumb through fingers.jpg|thumb|right|200px|The "fig sign" is an ancient gesture with many uses.]]

The "fig sign" is a gesture made with the hand and fingers curled and the thumb thrust between the middle and index fingers, or, rarely, the middle and ring fingers, forming the fist so that the thumb partly pokes out. In some areas of the world, the gesture is considered a good luck charm, in others it is considered an obscene gesture, and in still others it is used in the "I've got your nose!" child's game. This gesture is also the letter "T" in the [[American Sign Language alphabet]]. In [[International Sign]], which otherwise uses the same manual alphabet, "T" has been modified to avoid possible offense.

In [[ancient Rome]], this gesture was called the ''mano fico'', and was a fertility and good luck charm designed to ward off evil. Although this usage has survived in [[Brazil]], where carved images of hands in this gesture are used in good luck [[Amulet|talisman]]s, in many other cultures, such as Greece, Indonesia, Turkey, Cyprus and Russia, the sign has come to have an insulting meaning roughly equivalent to "screw you", based on the thumb being seen as representing a [[clitoris]] or [[sexual intercourse]]. In modern Russia this gesture is used mostly by kids with the meaning "screw you/no way". The same meaning is expressed by adults either with bent elbow (rude, very emphatic, non-classy), or with a "finger" (used mostly by city dwellers). The "finger" made it to Russian gesture language from Western movies. In modern [[Italian language|Italian]], the gesture is called the ''mano fica'', taken to mean "fig hand", as the Italian word for "[[fig]]" is ''fico'' (''ficus'' in [[Latin]]). The obscene connotations of the gesture may partly originate from the fact that a similar Italian word, ''fica'', is a slang term referring to the [[vulva]]. This sexual connotation may date back to ancient Roman times; some Roman amulets combine a ''[[phallus]]'' and a ''mano fico'' gesture. In [[Dante Alighieri|Dante]]'s ''[[Divine Comedy#Inferno|Inferno]]'', [[Vanni Fucci]] curses [[God]] with a "fig" gesture. [http://danteworlds.laits.utexas.edu/circle8b.html#vanni]

Also known as the [[Sicilian Fist]] in Sicily, worn as a good luck charm. * [http://www.italybyvip.com/1874.html Images of the "Sicilian Fist Charm" in Sicily]

The gesture is also used in a trick played by adults and parents, with the intention of convincing their child that his or her nose has been taken away. Someone, usually an adult, grabs at the child's nose and forms the fig sign, exclaiming, "I've got your nose, I've got your nose!" The thumb is supposed to be the child's removed nose.

Many [[neopaganism|neopagans]] use this gesture as a symbol of the [[mother goddess]] to help adherents identify one another. In this context, it is referred to as the "Sign of the Goddess". Its counterpart is the ''[[corna]]'' sign.

In [[The Gnostic Mass]] of [[Aleister Crowley]], this gesture is assumed by the priest throughout the Mass when his lance is not in his hand. It is a phallic device and symbolizes copulation, the fruit of which is a fig, traditionally appropriated to Jupiter the phallic sky god. The use of "the ficus" in the Gnostic Mass replaces the sign of benediction (mentioned above) used in Christian ceremonies.

===Finger Snap===
{{Unreferenced|date=September 2006}}
One of several gestures familiar to modern people primarily through old [[animated cartoons]], this gesture generally expresses a confident "screw you!" in the face of an adversary. The gesturer holds one hand out, palm up, in the direction of his antagonist and snaps his thumb and middle finger, generally accompanied by a high-nosed, "snooty" facial expression and followed by crossing the arms.

In some countries, particularly Great Britain, snapping the fingers is used to signify remembering or failing to remember. Snapping the fingers repeatedly at a constant rate is commonly used to signify that the person has forgotten something and is trying to recall it. This is often done with the fingers snapped close to the temple, as though literally 'jogging the memory,' and is associated with the phrase 'it's on the tip of my tongue.'

A single snap, sometimes emphasized by an arced swing of the arm, is used when someone is reminded of something by another person, particularly if it is a job or a chore they have forgotten to do, or as a sign of disappointment or regret. Some people also snap their fingers to catch the attention of others. This is informal - some people may find it rude or even threatening, as it is common for the gesturer to snap his fingers very close to the other's face. In some cases, this may be interpreted as a face-threatening act or a sign of contempt.

==="Hanging"===
This gesture is performed by holding a clenched fist at the side of the head, tilting one's head away from one's fist, and making a choking sound. It may also be accompanied by hanging the tongue loosely out of one's mouth, and rolling of the eyes back into the head. It is generally used to signify "what I would rather be doing". It can also be used to show suicide.

===Horns===
{{main|Corna}}
[[Image:gesture raised fist with index and pinky lifted.jpg|thumb|right|200px|Corna]]

Many [[neopaganism|neopagans]] use it as a symbol of the [[horned god]] to identify each other; in this context it is referred to as the "Sign of the Horned God". Its counterpart is the ''fig sign'', above.

Some say that it is meant to ward off — or to bestow — the [[evil eye]]. It is also a representation of the [[Devil]] by some [[Satanist]]s. The gesture's origin is believed to be an imitation of the shape of a goats head, which has many associations with the concept of Satan in [[Christianity]] [http://www.keyway.ca/htm2001/20010924.htm Satan's Goat]

It has a variety of other meanings as well, depending on culture and area. In some places, it is a sexual insult, charging a man with being a victim of [[adultery|cuckoldry]] (this insult is most common in [[Spain]] and [[Italy]] but is also used in Brazil). Perhaps because of its [[occult]] significance, it is used as a salute by fans of [[Devil horns#Heavy metal|heavy metal music]]. If one reverses the extended fingers, one gets the "inverted heavy metal salute" which can be given as a reply to a heavy metal salute. In this case, the sign is known as "devil horns".

Also a common hand gesture used by the University of Texas at Austin. The sign is also usually accompanied by the slogan "Hook 'Em Horns." The gesture is said to look like a head of a Longhorn, the University's mascot.
To [[Chaote]]s practicing [[Lovecraftian magick]], it is called the "Sign of Voor" or the "Voorish Sign".

===Kodály Hand Signs===
Named after [[Zoltán Kodály]], and largely defined by [[John Curwen]], Kodály Hand Signs are a way of representing musical notes by holding the hand in a certain position for each note. The basic concept of using gestures to represent notes is quite ancient, however near the end of the 19th century, the concept was formalized as a standard teaching method. Kodály Hand Signs are featured in the [[1977]] film [[Close Encounters of the Third Kind]].

===Knocking on wood===
{{main|touch wood}}
This signifies the neutralization of a [[jinx]]ing brought on by mentioning an either hoped-for or feared result. The knuckles are rapped on a nearby piece of wood (or, jokingly, someone's head). Usually this is only valid if done on bare (i.e. unpainted) wood. One possible reason for the tradition could have been from an [[animist]] culture who believed that the knocking would release spirits to protect them. It has also been said to stem from a belief that any nearby evil spirits who overhear somebody speaking of good fortune which has come his way may send some bad luck to offset it; knocking on wood was thought to keep the spirits from hearing. It is also known as "tapping wood" or "touching wood".

In Italy, one knocks on iron with the hand in the ''[[corna]]'' horns position.

===Middle finger===
{{main|The finger}}
[[Image:Middle finger.JPG|thumb|right|200px|"[[The finger]]" is a very common offensive hand gesture.]]
"The finger" is a gesture consisting of a fist with the middle finger extended. It appears to be universally understood as "[[fuck|fuck you]]"or get stuffed due to its resemblance to the penis. It is certainly thousands of years old, being referred to in Ancient Roman literature as the ''digitus infamis'' or ''digitus impudicus''. Performing this gesture is also called "flipping the bird" in countries where "the finger" is used. In other regions, "flipping the bird" refers to the raising of the middle and index finger with the back of the hand directed at the recipient. It can also mean "Victor" (see ''[[#V Sign|V Sign]]'', below) in some countries, which is not to be mistaken for the "Peace" gesture, which is done with the palm facing the recipient of the gesture, but in Britain and some other countries it is an offensive gesture, equivalent to "the finger". [[George W. Bush]] can be seen making the gesture while he was the Governor of Texas, while goofing off before beginning filming of a public address.<ref>[http://www.youtube.com/watch?v=o9Do-s1cdPk Bush "One-fingered Victory Salute" Video] </ref>

Former [[professional wrestler]] [[Stone Cold Steve Austin]] used the finger quite frequently in [[World Wrestling Entertainment|WWE]] shows. He raises both of the fingers to the crowd as a way of saluting to them. Also, he gestures the finger at his opponent before kicking them in the stomach and performing the [[Stone Cold Stunner]].

Comedian [[Dane Cook]] parodied the gesture with his "Super Finger" gesture, which consists of raising the middle finger, ring finger, and thumb on the same hand while lowering (or curling) the pointer and pinky finger. It is meant to be a more "powerful" version of "the finger".

The middle finger is also used to represent the number four when one counts in the binary system using one's fingers.<ref>[http://www.intuitor.com/counting/]</ref>

When this gesture is made with the palm facing forward, it is known to [[Chaote]]s practicing [[Lovecraftian magick]] as the "Sign of Kish". Another Lovecraftian sign is the "Sign of Koth", which consists of fully extending the index finger, middle finger, ring finger, and pinky, while the thumb is tucked against the flat of the hand.

=== Money sign ===
The thumb rubs repeatedly over the tip of the index finger and middle fingers. The ring finger and pinky touch the palm. This gesture is meant to resemble the act of rubbing two coins together (alternatively the act of counting paper bills) and has a general meaning of "money", or "expensive".

===OK===
{{main|Okay}}

This is the touching of the index and middle finger (or just index finger) with the thumb (forming a rough circle) with the raising of the remaining fingers. In the United States and most of Europe, it means "OK" and is inoffensive. The OK sign is used extensively in [[scuba diving]]. It can also mean "[[0 (number)|0]]," or "[[money]]," in [[Japan]].
However, in Germany, it is often seen on the Autobahn, as a silent way of calling someone an "Asshole" (with the fingers extended horizontally). Similar vulgar meanings are found in other countries, but usually you have to turn the 'Ring' upside down (supinated to show the ring in front) like this example from [http://jeroenarendsen.nl/2006/05/butthole-is-not-ok.html Brazil]. It is then a sexual or scatological gesture referring to the [[anus]]

===Moutza (Palm of hand)===
{{main|Moutza}}
In most places, a palm raised towards somebody means "stop".

In [[Greece]], the palm of the hand thrust towards somebody with the fingers splayed is an offensive gesture equivalent to giving the finger. The gesture is known in Greek as "moutza". It originates from the Byzantine punishment of parading a chained criminal around town with his face smeared with [[cinder]], or ''moutzos'' in Greek. An even more offensive version is achieved by using both hands to double the gesture, and smacking the palm of one hand against the back of the other, in the direction of the intended recipient. Both the one-handed and the two-handed versions of this gesture can be (and often are) combined with the term "''na''!", meaning "here you go!" or "there!", or "''na, malaka''!", meaning "there, you wanker!"

===Salute===
{{main|Salute}}
There are many forms of [[salute]] gestures, most of which are used to denote respect or obedience for an authority. A common [[military]] hand salute consists of raising the right hand, held flat, to the right eyebrow. [[Scouting]] organizations use related salutes. The armies of various countries adopt slightly different forms of salute: in the United States, the military salute places the hand directed outward over the eyebrow, like a visor; in the United Kingdom armed forces, the hand is brought to the forehead palm outward in military and air force contexts, whereas the naval salute is as in the US forces - the US forces derived their saluting habits from the [[Royal Navy]].

One of the most infamous forms of salute is the "[[Hitler salute]]", which is performed by extending the whole right arm, palm outstretched and facing down, upwards into the air at approximately a 45 degree angle from the ground. Sometimes, this is accompanied by holding the index and middle fingers under the nose, representing Hitler's iconic moustache. This gesture is associated with [[Nazism]] and its leader, [[Adolf Hitler]], as well as with [[Germany]] during [[World War II]]. It is occasionally performed to mock someone or something for perceived [[authoritarianism]] or [[bigotry]]. This gesture was based on the [[Roman salute]], and it was in that capacity that it was revived by [[Tennis Court Oath|French Revolutionaries]] and later by [[Benito Mussolini]]'s [[Fascism|Fascist]] party.

In some countries, mostly in Europe, it is forbidden by law to perform this gesture, although this does not deter [[Neo-Nazism|Neo-Nazis]] and white supremacists from using the gesture in public rallies. Even in other countries, it is generally considered taboo to use the gesture, and this partly caused the [[United States]] to abandon the similar [[Bellamy salute]] used when reciting the [[Pledge of Allegiance]], in favor of the current hand-on-heart gesture.

===Shaka===
{{main|Shaka sign}}
[[Image:gesture raised fist with thumb and pinky lifted.jpg|thumb|right|200px|The "[[shaka sign|shaka]]" sign is a common greeting in beach and surfer culture.]]

The "shaka" sign is a common greeting gesture often associated with [[Hawaii]], [[California]], and [[beach]] and [[surfing|surfer]] culture in general. It consists of extending the thumb and pinky finger while keeping the three middle fingers curled, and is often described colloquially as the "hang loose"or "chilax" gesture. It is similar to [[American Sign Language]] letter "''Y''", where a fist is also made with only the thumb and pinky extended. The sign is often followed by waving as a greeting or acknowledgment. It can be used when driving as a signal of thanks to other drivers (for example, someone who stopped to let another driver onto the road from a driveway).

The "shaka" sign is also the greeting gesture for members of [[Alpha Phi Alpha]] Fraternity, Inc. which is the "phi" sign. All African-American Greek fraternities and sororities have hand greeting gestures.
====Similar gestures====

In Britain and Northern Europe the symbol is used as a signal for owners of older model [[Volkswagen]] vans when passing on roads. The silhouette of the hand reveals a "W"-shaped outline along the top of the hand standing for Volkswagen.

In Spain and Italy, if the thumb points to the mouth, it means "drinking", since it is similar the shape of a ''[[porrón]]'' vessel. This is also true of the [[United States]], [[Portugal]] and [[Brazil]].

In some countries, if the thumb points to the mouth, it can also represent [[marijuana]] usage, in particular the use of a [[bong]]. This is usually accompanied by a sucking noise.

In China, it is also the sign for the number six.

A similar gesture is the "call me" sign, which also has the pinky finger and thumb outstretched, but then also holds it up to the ear, to signify a telephone. This gesture is a common way to silently tell someone to call him or her, such as to continue a conversation in private.

It is also used by [[FC Barcelona]] player [[Ronaldinho]] as part of his goal celebration.

In India, rolling the shaka in a winding motion signifies that the listener does not believe what is being said and that the speaker needs to "spool in the yarn from spinning out too far".

In [[American Sign Language]], a "rolling" version of this sign indicates the activity "play", often used by non-verbal (i.e. pre-speech children) people to ask if one wants to play or that they signer wishes to play.

==="Thanks!" Salute===
Another gesture familiar from vintage cartoons, this is performed by sweeping an opened hand from near one's brow toward the person being addressed, and expresses gratitude. It is adapted from [[American Sign Language]], and alludes to tipping your hat or cap.

===Three middle fingers===
Gestures consisting of fully extending the index, middle, and ring fingers with the thumb and pinky tucked together under the palm have had a variety of meanings over the years.

The gesture was also used by [[Bosnian Croat]]s as a victory sign, representing the Christian [[Trinity]], during the [[Bosnian War]]. To [[Chaote]]s practicing [[Lovecraftian magick]], this gesture is known as the "Sign of the Elders." With the palm facing outwards, the fingers closed (without gaps), the right hand's fingertips to the same-side temple, it is used by the [[scouting|Boy scouts]] as their identifying [[salute]].

In the United States, when the back of the hand faces outwards, this gesture is often used as a [[euphemism]] for "[[#middle finger|the finger]]." It is used especially when a jocular effect is desired. Originally, an accompanying verbal explanation was usual — "Read [[subtext|between the lines]]," referring to the common English expression denoting that one must read carefully to glean the subtle meaning in a passage — but this phrase is now commonly omitted.

===Thumbs up, thumbs down===

A closed fist held with the thumb extended upward or downward is a gesture of approval or disapproval respectively. These gestures have become metaphors in English: ''"My boss gave my proposal the thumbs-up"'' means that the boss approved the proposal, regardless of whether the gesture was made — indeed, the gesture itself is unlikely in a business setting.

The source of the gesture is obscure. Though a favorite of Hollywood '[[sword and sandal|swords and sandals]]' epics, where the "thumbs down" symbol means that the loser in a gladiatorial combat should be put to death, recent research suggests the meanings of the symbols have changed over the years. In [[1997]], Professor [[Anthony Philip Corbeill]] of the [[University of Kansas]] concluded that the thumbs up actually meant "Kill him," basing his assertion on a study of hundreds of ancient artworks. Thus, the "thumbs up" was an approval of the gladiator's request to kill his vanquished foe rather than a vote to allow the defeated to remain alive. Corbeill wrote that a closed fist with a wraparound thumb was the indication for a gladiator's life to be spared.

[[Image:Jean-Leon Gerome Pollice Verso.jpg|thumb|right|200px|''Pollice Verso'' by Jean-Léon Gérôme, [[1872]] is the immediate source of the "thumbs down" gesture in [[popular culture]].]]

In [[Latin]], the "thumbs up" gesture is called ''pollice recto'', "thumbs down" is ''pollice verso''. It is not certain that the contemporary gestures are identical to the gestures performed in [[ancient Rome]]. The current version was popularized by a widely reproduced [[academic art|academic painting]] by the [[19th century]] artist [[Jean-Léon Gérôme]], whose ''Pollice Verso'' depicts a triumphant gladiator standing over a fallen foe, looking up into the [[bleacher]]s for the verdict of the crowd.

Additionally, [[Desmond Morris]]' ''Gestures: Their Origins and Distribution'' traces the practice back to a [[medieval]] custom used to seal business transactions... Over time, the mere sight of an upraised thumb came to symbolize harmony and kind feelings... The gesture's popularization in America is generally attributed to the practices of World War II pilots, who used the thumbs up to communicate with ground crews prior to take-off. American GIs are reputed to have picked up on the thumb and spread it throughout Europe as they marched toward Berlin." [http://slate.msn.com/id/2080812/]

More recently, these gestures are associated with [[film|movie]] [[review]]s, having been popularized by [[Gene Siskel]] and [[Roger Ebert]] in their televised reviews — the thumb up meaning a positive opinion of a film; the thumb down meaning a negative one. One or two thumbs up, often held over the head, may also be used by athletes in celebration of a victory.

"'Thumbs up' traditionally translates as the foulest of Middle-Eastern gesticular insults — the most straightforward interpretation is 'Up yours, pal!' The sign has a similarly pejorative meaning in parts of West Africa, South America, Russia, Iran, Greece, and Sardinia, according to Roger E. Axtell's book ''Gestures: The Do's and Taboos of Body Language Around the World''."[http://slate.msn.com/id/2080812/]

[[Hitchhiker]]s traditionally use a thumbs up gesture to solicit rides from oncoming vehicles, although in this presentation the arm is generally outstretched with the palm and closed fingers facing the motorist. People who have the genetic ability to bend the tip of their thumb backwards are said to have "hitchhiker's thumb," which is a reference to the original gesture.

Additionally, supporters of [[Texas A&M University]] athletic teams use the thumbs-up sign, associated with the cheer, "Gig 'em, Aggies." The Thumb refers to a "gig" used for hunting frogs. The saying came when the Aggies had a big rival in the Southwest Conference in the TCU Horned Frogs.

Thumbs up and thumbs down are extensively used in scuba diving as commands to ascend or descend.

[[World Wrestling Entertainment|WWE]] Superstar [[Dave Bautista|Batista]] uses this gesture to signify his finisher, the [[Batista Bomb]].

=== Tsk-tsk ===
Palm towards the recipient, all fingers closed except for the index, which alternates from left to right, like a [[metronome]]. In English-speaking countries it has a disapproving meaning and can be accompanied by a "[[tsk|tsk-tsk]]" sound. This is also known as "finger-wagging".

In Italy and Brazil it simply means "no", and does not have any patronizing connotation.

===V sign===
[[Image:Nixon-depart.png|thumb|right|200px|[[Richard Nixon]] gives the V-sign one last time after resigning from the presidency.]]
{{main|V sign}}

The "V sign" is made by lifting the middle and index finger with the palm of the hand facing the recipient (and the remaining fingers clenched). It was associated with the [[catchphrase]] ''"V" for Victory'' in [[World War II]]. In the [[1960s]], it came to be known as the "[[peace]] sign," the gestural equivalent of the [[peace symbol]]. It was associated with British prime minister [[Winston Churchill]] during World War II, and later, with U.S. president [[Richard Nixon]]. It is also the sign for the letter V in [[American Sign Language]].

This sign is frequently used by the Japanese, most times holding up 2 "V" signs very close to either side of their face with a big grin during pictures.

In the UK, Australia, and some other countries, reversing the V sign so that the back of the hand facing the recipient is seen as the equivalent of giving [[finger (gesture)|the finger]]. Popular myth supposes it was originally a taunt by English Longbow Archers towards the French who were known to cut off an English Archer's first and middle fingers if captured.

Additionally, due to its use in an advertisement for the Australian made Valiant Charger (which ceased production around 1980) many people still display the V sign, in homage to the ad, and the car, if that vehicle happens to be driven past. Hardly an every day occurrence, but of some trivial interest.

===Vulcan salute===
{{main|Vulcan salute}}

The Vulcan salute consists of a raised hand, palm outward, fingers extended, with the index and middle finger kept close together, and the ring and pinky finger close together, with a "V" shaped space between them, and the thumb sticking out alone.

This gesture is associated with the phrase "Live long and prosper", and derives from ''[[Star Trek]]'', where it is used as a salute by fictional humanoid species the [[Vulcan (Star Trek)|Vulcans]].

It was introduced by [[Leonard Nimoy]] in his character of [[Mr. Spock]] and is drawn directly from the benedictory gesture made with both hands by a [[Kohen]] (priest in Judaism, a descendant of Aaron) during the [[Priestly Blessing]] ([[Hebrew language|Hebrew]]: ''Birkat Kohanim''). The [[Kohen|Kohanim]] recite a blessing while performing this "gesture" and the other congregants respond with [[Amen]]s.

This gesture is also known as the "Spocker" in allusion to [[Shocker (hand gesture)|the Shocker]].

===Wanker===
[[Image:Fingers and thumb in circle downward motion.jpg|thumb|right|200px|Wanker]]
A loose fist (with all fingers forming a cylindrical shape) is made, and shaken up and down (or sometimes, back and forth) at the wrist.

The gesture is imitative of the motions of male [[masturbation]]. Its meaning is equivalent to the word [[wanker]] or implies something is of little importance. If directed to a person or group, who are not necessarily present, it is considered a display of contempt toward them.

The name for this gesture is described by speakers of [[American English]] as a [[Britishism]].

[[Image:Portugal Wanker Gesture.jpg|thumb|right|200px|The Overhand Portuguese Wanker Gesture]]

In [[Portugal]] they use the wanker gesture but with the palm facing the ground thereby implying that the person is masturbating someone else rather than themselves. As such this has [[homosexual]] or promiscuous implications when directed at someone instead of the milder suggestion that they enjoy self-gratification.

In the United States, this gesture can indicate contempt, particularly indicating that the gesturer thinks something is a waste of time.

===Wave===
A wave is a gesture in which the hand is raised and moved back and forth, as a [[greeting]] or sign of departure. The orientation of the hand varies by culture and situation. In many cultures, the palm is oriented toward the recipient of the wave.

In Chinese culture, orienting the hand palm-down and waving it up and down signifies "come here", rather than a greeting. 

===Whoop-Dee-Doo===
Point the index finger up and rotate it. This is a usually used as a response gesture to indicate something is uninteresting or irrelavent. Similar to saying a sarcastic "Whoop-Dee-Doo" or "Big deal".

==Using two hands==
{{main|Hand gesture}}
===Awkward Turtle===
The Awkward Turtle is a gesture made after something awkward just happened, or when there is an awkward silence.
To perform an awkward turtle there are three steps to take. First, place hands on top of each other. Next, move thumbs out and away from the hands. Finally, rotate the thumbs.

Nowadays the gesture is used in the United States to hush children, or to calm participants in a heated argument. In [[Japan]], the same gesture may be used to request the check when dining at a restaurant (see also [[#Check, please|Check, please]], above).

==="Gills"===
This gesture involves holding the backs of the wrists against the jawline (with elbows outstretched) and then waggling one's fingers. The gesture is often accompanied by a feminine-voiced "Ooooo!" which rises and falls in intonation. It is used when one would normally say (sarcastically) "well aren't you clever?", or to imply that someone is acting too posh for their station. It is peculiar to Scotland owing to its use in Scottish TV sketch show [[Chewin the Fat]].

==="Shame on you"===
This gesture involves pointing at a person with the index finger of one hand while rubbing the pointed finger with the index finger of the opposite hand. The rubbing motion is directed toward the intended recipient and is repeated at least three times. It is used to imply that the targeted person should feel shame.

===Time-out===
The "time-out" gesture — a "T" formed with the hands, with one hand with flat palm placed perpendicular to the other hand with flat palm, roughly in the center — originates in American sports. It was, and is, used where a brief [[sport time-out|pause in play]] is called for, such as to make substitutions. In [[basketball]], the gesture is used to indicate that a player or coach is guilty of a [[technical foul]].

===Whatever!===
A gesture associated with [[Valley Girl]]s. Forming the letter "W" by extending the two index fingers upward and touching the thumbs together at a 45 degree angle, this hand sign is used silently or in conjunction with an uttered "Whatever!" (pronounced with a slight pause after the first syllable, emphasis on the second, and drawing out the third syllable to a hard "r"). It is a sarcastic response dismissing whatever has just been said to the person making the gesture.

==Hand with body gestures==
{{Mergeto|Hand gestures|Talk page|date=April 2007}}
===Bent elbow===

This is performed in two parts: first, the right hand is placed in the elbow crook of the left arm. The left arm is then raised (fist clenched) at the victim in a smooth and continuous motion. While the motion is essential to the gesture, the choice of arm is not. This gesture is associated with [[Italy|Italians]] and is considered a more theatrical and physically exuberant version of the [[finger (gesture)|finger]], and may even be combined with the finger. In Italian it is known as the ''gesto dell'ombrello'', meaning literally "the umbrella gesture." It is typically used in two different situations: 1) to answer "no way!" in an extremely emphatic (and quite vulgar) way; 2) after a triumph against some unfair enemy, with a sense of revenge. The gesture is frequently made stronger by crying "toh!" or "tiè!", both meaning "take this!", at the precise moment the hand touches the crook of the elbow.

This gesture is also in use in [[France]] as ''bras d'honneur'' (arm of honour), where it is usually understood as ''va te faire foutre'', still meaning "fuck off." In [[Spain]] and [[Portugal]], it is a ''corte de mangas'' ("[[sleeve]] cut") or a ''manguito'' (a cover formerly worn by public services bureaucratic workers on the arms to protect one's sleeves from ink splatters) respectively and is done with the left hand on the right elbow, without the continuous motion. In [[Portugal]], the iconic fictional character [[Zé Povinho]], created by [[Bordalo Pinheiro]], is usually depicted performing this gesture. This gesture, known as ''banana'', was also once used in Brazil with the meaning of "fuck you", but it has not been used since the middle of the 90's.

The gesture is sometimes used repetitively by fans at [[Citizens Bank Park]] in [[Philadelphia]] when the [[Phillies]] face the [[Atlanta Braves]] as a [[parody]] of the Braves' [[tomahawk chop]], and this usage is known as the "[[South Philly]] tomahawk chop" due to the gritty reputation of [[Philadelphia]] sports fans.

The gesture above has long been known in Slavic countries and Greece in the above senses plus "fuck you", without any standard name. In [[Poland]] its name has been standardized to "Kozakiewicz's gesture", after Polish [[pole vault]] jumper [[Władysław Kozakiewicz]], who had shown this gesture to the jeering Russian public during the [[1980 Summer Olympics]] in [[Moscow]].

===Biting one's thumb===


[[Biting one's thumb]] was an old rude British gesture. It is comparable to "[[#middle finger|the Finger]]" in modern terms. In [[William Shakespeare]]'s play ''[[Romeo and Juliet]]'', Sampson bites his thumb at the Montagues (Act 1, Scene 1).

The gesture does not literally involve biting the thumb. The fingernail of a thumb is placed behind the upper teeth, with the thumb thus pointing upwards, and the thumb is then bent forwards, the fingernail making a clicking sound as it flicks past the teeth.

An equivalent gesture still persists in [[Italy]].

=== Biting one's hand ===
In Sicily, biting one's flat hand or fist is a powerful threat.

===Bowing, kneeling, kowtowing===
A [[bowing (social)|bow]] is a gesture of respect involving lowering the head, usually performed by a social inferior to a social superior. Various cultures have different degrees or ways of performing the bow; [[China]] and [[Japan]] are particularly associated with elaborate and formal bowing. Bowing is also done by many groups as a ritual associated with [[prayer]]. In the Western world, women [[curtsey]] rather than bow. [[Kneel]]ing and "[[kowtow]]ing" are more extreme or elaborate forms of self-abasement before a social superior.

===Choking sign===
[[Image:Chokinggesture.JPG|200px|thumb|right|The "Choking" sign]]
The standard gesture to indicate that one is [[choking]] is to hold the throat with both hands as if strangling oneself. This is recognized as a request for immediate [[first aid]] for choking. It is promoted as a way to prevent onlookers from confusing the victim's distress with some other problem, such as a [[myocardial infarction|heart attack]], when the person cannot speak. The gesture is sometimes used metaphorically to refer to someone or something "choking" in the slang sense of failing at something while under pressure, for instance at an athletic event.

===Crossing oneself===
{{main|Sign of the cross}}
The "[[sign of the cross|sign of the Cross]]" is the use of the right hand to touch the forehead, chest, left shoulder, and right shoulder, consecutively. It represents the [[Christian cross]]. (Roman Catholics crossing themselves touch the forehead, chest, left shoulder, then right shoulder; Byzantine (Eastern) Catholics and Eastern Orthodox Christians touch the right shoulder before the left, with the thumb and first two fingers joined — symbolizing the Trinity — and the tips of the last two fingers touching the palm, symbolizing the dual nature of Christ in one being. )

This gesture is used by [[Roman Catholic]]s, [[Eastern Orthodox Church|Orthodox Christians]], and some other Christian groups in [[prayer]]s, to perform blessings, and as a salute before entering a [[church]] or similar place of religious significance. It is also used in various kinds of Christian [[folk religion]] to avert [[evil]] or [[bad luck]].

===Cutthroat===
[[Image:Cutthroatgesture.JPG|200px|thumb|right|The "Cutthroat" sign]]
This gesture is performed by drawing the hand, or a finger or two, across the throat. It represents slitting the throat with a knife, and means that the gesturer or someone else is metaphorically being killed. It is rarely if ever used literally to refer to death, though it is occasionally used as a theatrical threat ("I'm going to kill you"). In these contexts, it is sometimes accompanied by a harsh "kkkkkch" sound.

This gesture can also mean to "cut," "stop," or to discontinue a particular action. It can also be used to indicate something has ended or a previous process has concluded. [[Scuba diving|Scuba]] divers use this gesture with the palm swept across the throat to indicate that they have run out of air. Airport ground personnel also use this gesture to indicate a variety of things (due to the loud environment), such as baggage offload has completed or the last of the passengers have disembarked. In this context, it can be understood to mean: "That's it."

Also used by movie personnel when having to signal a cessation of activity under silent conditions.

Additionally, [[World Wrestling Entertainment|WWE]] Superstar [[The Undertaker]] uses this gesture to signify his signature moves, the [[Chokeslam]], [[Powerbomb#Elevated powerbomb|Last Ride]], and [[Piledriver (professional wrestling)#Tombstone piledriver|Tombstone piledriver]], as did [[Chris Benoit]] until his recent death.

=== Drinking sign ===
In UK, the gesture for drinking (used for example as an invitation to "go down the [[pub]]") is made by putting the back of the thumb just below the lower lip, while the other fingers are close together as if holding an imaginary [[pint]] of beer, tipping it repeatedly. This gesture can also be used to imply that somebody is drunk, either literally or insultingly.
In other countries, the shaka sign is used in a similar way, as described above.

===Flipping the fingers out from under the chin===

A [http://news.bostonherald.com/localRegional/view.bg?articleid=132932 traditional Sicilian gesture] analogous in meaning to the raised middle finger. This gesture became the center of a controversy in March of 2006, when [[U.S. Supreme Court|Supreme Court]] [[Associate Justice]] [[Antonin Scalia]] was photographed allegedly making the gesture to illustrate his response to his critics. Scalia later claimed that he used a different gesture, waving his fingers beneath his chin, a gesture translating to "I couldn't care less."
===Forehead Clunk===
This gesture indicates stupidity, usually a minor and immediately recognized slip of logic, judgment, or speech; and is performed by striking the forehead with the heel of the hand.

=== Hand over heart ===
This gesture involves placing one's right hand, palm outstretched and facing in, over one's heart. Male [[hat]] or cap wearers typically remove their hats and hold them in this hand. In some cultures, it is used as a gesture of respect towards [[flag]]s or during singing of a [[national anthem]]. In the United States, it is also performed as a part of the rituals of the [[Pledge of Allegiance]]. It can also be used to indicate sincerity, shock, or hurt; in which case, a balled hand has the same meaning.

===Loser===
This gesture is performed by raising the index finger and thumb of your right hand perpendicular to each other so that they form the letter "L". It is then placed onto one's forehead. It signifies that the person to whom this gesture is directed is a loser.
However, when the opposite hand is used, the gesture becomes highly ironic.

===My eye===

In France, Germany, and other parts of Europe{{Fact|date=September 2007}} it is common to point your index finger at your eye and even pull the skin under the eye lightly down to emphasize the presenting of the eye. The gesture displays disbelief or that a certain statement is made jokingly, similar to winking in American culture.

In Japan, tugging at the eye, often accompanied by sticking out one's tongue, is used as a childishly offensive gesture, or to indicate boredom.

In Italy, Portugal, Brazil and all Spanish-speaking nations it means "watch out" (POR, ITA:''occhio!'',SPA:''¡ojo!''), and is used for warning or threatening.

In Denmark it can be a joking threat, often accompanied by the phrase: "Because the eyes are what you takes care for the most".

===Nonsense===
Performed by waving the palm of your hand in front of your face, it may be used to tell the other person that an idea he or she had was nonsense.

In [[Portugal]], this gesture usually means the person being referred to missed an extremely obvious detail.

===Nose thumbing ===
For this gesture, also known as "cocking a snoot", "giving the five-finger salute", "cocking a snook", or Queen Anne's Fan, the thumb is placed on the tip of the nose, with the remaining fingers of the hand extended and waggled freely. This gesture can be ended with a dramatic flicking of the thumb away from the end of the nose and towards the recipient. It is used in (gentle) mockery of someone. It dates back to at least the 18th century and is probably much older.

To add emphasis, the gesture can be made using both hands, connecting them by touching the little finger of the first hand with the thumb of the second, and waggling the remaining seven fingers. It is frequently accompanied by [[blowing a raspberry]], or by sticking out the tongue.

===Over the Head===
A hand is extended and passed over the head with the palm facing the head. This is often accompanied with a whooshing sound or an exclamation of "Over your head!". This indicates that the receiver has failed to comprehend or notice something obvious.

===Screwing The Forehead===
A finger is placed against the temple, as if pointing at it, and a screwing motion, as if making a dimple, is made by twisting the wrist. In Italian culture, this indicates that the person referred to is "crazy" or "nuts."

===Suck my dick===
This gesture is performed by crossing the outstretched arms across the thighs, putting emphasis on the [[groin]]. This was used by popular professional wrestling [[stable (wrestling)|stable]], [[D-Generation X]].

There is a variation to this where a fist is made and shook near the mouth while bulging ones tongue against their cheeks to mimic fellatio.

===The Turkish Fig===
In [[Turkey]] and [[Greece]], putting the thumb between the middle and index finger of the right hand and making a fist is called "the fig" and is extremely offensive. In Turkey, taking that fist, placing it in the left hand and then pushing it out to make a slapping sound with the wrist of the right hand is even more offensive, and is usually accompanied by a string of obscenities. These gestures are often seen at soccer games.

===Touched / screw loose===
Tapping one's index finger against the head indicates that a person or an idea being discussed is insane or "touched in the head". A similar, more elaborate gesture uses a circling motion of the finger at the temple or side of the head. This signifies that the person is "mixed up" or "has a screw loose". In Germany, tapping or pointing to the temple is used as an insult, often with the accompanying phrase "du hast einen Vogel." While this literally means "You have a bird," it is idiomatic for saying that you are insane. Also, in Indonesia, drawing a line across the forehead with the side of the right index finger denotes a similar meaning.

A variant of this one is the suicide. Make a gun with your hand and pretend to shoot point blank at your own temple. It can be accompanied with sticking out the tongue or a shooting sound for full effect, and often implies that the speaker is a "complete idiot". A more recent use of this is in the movie, "40-Year Old Virgin" where one of the characters, after being bored with a conversation, proceeds to aim at his temple and pretend to fire. Afterwards, he uses his other hand and does a reverse cupping motion outward from the other side of his head to signify his brains splattering out.

In Japan, a variation of this is knocking on the temple with the knuckle of the index finger. This is usually used in reference to the signer; "I'm such an idiot!"

===Twisting The Cheek===
Thumb and forefinger are placed against the cheek, and a screwing motion, as if making a dimple, is made by twisting the wrist. In Italian culture, this can mean "I see a pretty girl" or, just generally mean "Wow!"

==="Wiping" one's forehead===
The act of wiping one's own forehead, regardless of whether sweat has actually formed there, is a sign indicating many things such as "That was close" or "What a relief". It can also be used to express relief after some hard work, or to express feeling hot.

==Body and facial gestures==
{{further|[[Facial expression]]}}
[[Image:Eyeroll.JPG|thumb|right|200px|Rolling one's eyes can express exasperation or condescension.]]

Many gestures utilize only the face or body, without the hands.

===Eye-rolling===
Performed by rotating the eyes upward, it indicates condescension, contempt, boredom, or exasperation. This is often referred to as "rolling ones eyes to Heaven," as though wishing for a divine intervention for a rescue from boredom, frustration, etc.

===Mooning===
[[Mooning]] is the act of displaying one's [[nudity|bare]] [[buttocks]] by lowering the back side of one's [[trousers]] and [[underpants]], usually without exposing the [[genitals]]. Mooning is used in some cultures to express protest, scorn, disrespect, or provocation. It can also be done for [[shock value]] or fun.

===The "peacock"===
Expresses superiority or domination combined with a certain degree of smug arrogance. Performed by pushing the chest up and out at the front as well as tilting the face slightly upward. This may be accompanied by motions of hooking both thumbs under one's [[lapels]] or [[suspenders]] even if they are not present.

{{Gestures}}

==References==
{{reflist}}

[[Category:Gestures]]

Basic I/O

2007-08-22T06:53:10Z

24.113.198.14: /* Last words about I/O */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is abbreviated I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio/video (not in that order of course). These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyze these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms are related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computers but also in our cellular phones, in our televisions, robots, various children's toys, trains, airplanes, warheads, missiles, et cetera. Almost everything is a computer.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input may be the children age of school in Turkiye Istanbul, and the output may be the average age of these children as displayed on the screen or directed elsewhere (e.g. printer, file on hard disk).

The input on an iron cutting machine will be the iron cutting style designed and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Examples: entry of names, entry of birthrates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG
* graphic numeric input example: Drawing Programs, Cameras
* mechanical input. This is for non-electrical computers: the paper with holes input in a textile machine.
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: CAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence micro robots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this collaborative work

Note:Modified significant portions.
Removed Opinionated statements without references, removed references to specific programs that were not relevant.

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about computers.

A computer scientist is not limited to electrical and electronic devices.

Note:Chopped off more unreferenced opinions and philosophical speak.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]

Basic I/O

2007-08-22T06:50:02Z

24.113.198.14: /* Input Output on end user level */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is abbreviated I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio/video (not in that order of course). These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyze these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms are related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computers but also in our cellular phones, in our televisions, robots, various children's toys, trains, airplanes, warheads, missiles, et cetera. Almost everything is a computer.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input may be the children age of school in Turkiye Istanbul, and the output may be the average age of these children as displayed on the screen or directed elsewhere (e.g. printer, file on hard disk).

The input on an iron cutting machine will be the iron cutting style designed and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Examples: entry of names, entry of birthrates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG
* graphic numeric input example: Drawing Programs, Cameras
* mechanical input. This is for non-electrical computers: the paper with holes input in a textile machine.
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: CAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence micro robots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this collaborative work

Note:Modified significant portions.
Removed Opinionated statements without references, removed references to specific programs that were not relevant.

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about PCs.

A computer scientist is not limited to electrical and electronic devices. In today's world where expertise became a unique way to find a job, it has resulted in limitation on human abilities used. So science has just reached a paradox.
To go out of this paradox, I suggest the following, consider computer not only as electroinic devices, but all.
Today computer scientists act as if the computer is just a PC. What about biomedical or what about industry?
The first computer was created before electricity was created. So the input/output has been invented much more before Edison.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]

Basic I/O

2007-08-22T06:35:58Z

24.113.198.14: /* Machine Input Output */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is abbreviated I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio/video (not in that order of course). These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyze these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms are related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computer but also in our cellular phones, in our televisions, robots, children's toys, trains, airplanes, warhead missiles, etc. Almost everywhere there are computers.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input is the children age of school in Turkiye Istanbul, and the output will be the average age of these children as displayed on the screen or on the printer.

The input on an iron cutting machine will be the iron cutting style designed in AutoCAD and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Example: entry of names, entry of birtdates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG, MPEG
* graphic numeric input example: AutoCAD inputs, Corel Draw and Photoshop as input
* mechanical input. This is for non electrical computers: the paper with holes input in the textile machine
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world. The personal computer is so far just a copy of maybe a microscopic part of our brain. You must never forget that a computer still cannot dream or have psychological disturbance, or create something. So I will place on the highest place and on the center of any study the mind of human and animals.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: AutoCAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence microrobots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this whole text is my mind output by the use of my fingers

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about PCs.

A computer scientist is not limited to electrical and electronic devices. In today's world where expertise became a unique way to find a job, it has resulted in limitation on human abilities used. So science has just reached a paradox.
To go out of this paradox, I suggest the following, consider computer not only as electroinic devices, but all.
Today computer scientists act as if the computer is just a PC. What about biomedical or what about industry?
The first computer was created before electricity was created. So the input/output has been invented much more before Edison.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]

Basic I/O

2007-08-22T06:33:47Z

24.113.198.14: /* Machine (computer) Input Output */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is abbreviated I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio video. These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyse these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms is related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computer but also in our cellular phones, in our televisions, robots, children's toys, trains, airplanes, warhead missiles, etc. Almost everywhere there are computers.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input is the children age of school in Turkiye Istanbul, and the output will be the average age of these children as displayed on the screen or on the printer.

The input on an iron cutting machine will be the iron cutting style designed in AutoCAD and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Example: entry of names, entry of birtdates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG, MPEG
* graphic numeric input example: AutoCAD inputs, Corel Draw and Photoshop as input
* mechanical input. This is for non electrical computers: the paper with holes input in the textile machine
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world. The personal computer is so far just a copy of maybe a microscopic part of our brain. You must never forget that a computer still cannot dream or have psychological disturbance, or create something. So I will place on the highest place and on the center of any study the mind of human and animals.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: AutoCAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence microrobots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this whole text is my mind output by the use of my fingers

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about PCs.

A computer scientist is not limited to electrical and electronic devices. In today's world where expertise became a unique way to find a job, it has resulted in limitation on human abilities used. So science has just reached a paradox.
To go out of this paradox, I suggest the following, consider computer not only as electroinic devices, but all.
Today computer scientists act as if the computer is just a PC. What about biomedical or what about industry?
The first computer was created before electricity was created. So the input/output has been invented much more before Edison.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]

Basic I/O

2007-08-22T06:33:27Z

24.113.198.14: /* What about input output */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is abbreviated I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine (computer) Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio video. These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyse these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms is related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computer but also in our cellular phones, in our televisions, robots, children's toys, trains, airplanes, warhead missiles, etc. Almost everywhere there are computers.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input is the children age of school in Turkiye Istanbul, and the output will be the average age of these children as displayed on the screen or on the printer.

The input on an iron cutting machine will be the iron cutting style designed in AutoCAD and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Example: entry of names, entry of birtdates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG, MPEG
* graphic numeric input example: AutoCAD inputs, Corel Draw and Photoshop as input
* mechanical input. This is for non electrical computers: the paper with holes input in the textile machine
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world. The personal computer is so far just a copy of maybe a microscopic part of our brain. You must never forget that a computer still cannot dream or have psychological disturbance, or create something. So I will place on the highest place and on the center of any study the mind of human and animals.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: AutoCAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence microrobots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this whole text is my mind output by the use of my fingers

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about PCs.

A computer scientist is not limited to electrical and electronic devices. In today's world where expertise became a unique way to find a job, it has resulted in limitation on human abilities used. So science has just reached a paradox.
To go out of this paradox, I suggest the following, consider computer not only as electroinic devices, but all.
Today computer scientists act as if the computer is just a PC. What about biomedical or what about industry?
The first computer was created before electricity was created. So the input/output has been invented much more before Edison.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]

Basic I/O

2007-08-22T06:31:34Z

24.113.198.14: /* Introduction to advanced level of computer science: */

== Introduction to advanced level of computer science: ==

If you arrived at this level of lesson, you may consider yourself a novice computer engineer.

The reasons is because you have now a basic knowledge of the computer as hardware, a beginner level on algorithms and beginner level on programming.

Now you will be confronted more and more in making a choice on your studies.

Getting an advanced level on hardware, on theory of computer science , or getting more on programming side.

This lesson will guide you on this choice. But whatever the choice is, you must have a general knowledge of computer science. Because on whatever the expertise you choose, you will be confronted to the problems on other parts of computer science. For example lets consider you choose to be a programmer. You must have knowledge on hardware, so as to be able to program for specific instances in hardware to solve bugs.

== What about input output ==

So now how all these are related to input output? The answer is, the input output is the main aspect of the computer science. It defines the whole system. It is related to system theory of Bertrand Bertalanfy.
Every system in the world is open system. An open system always has input and output. No system can live if it won't adhere to this rule; it will be destroyed. In contrast, a closed system can live without an input or output. It is a self sufficient system. No closed system has ever been discovered.
I recommend the lecture of Bertrand Bertalanfy to gain further knowledge on this.
So a computer is an open system that needs an input and makes an output.
Input and output is not only related to personal computer but also other devices. About this I recommend a lecture on the theory of communication, especially Claude Shannon and Norbert Wiener.

Input and output is spelled I/O.
There are many levels of input on todays personal computers. To first understand I/O I will talk about the computer input and output. So here is the plan of our study:
* Machine level I/O
* Coding level I/O
* And finally End user level I/O
As you may see here all of these levels need special expertise. The further you go here, the more you will get special knowledge on the level you chose. And any level you choose here, the expertise is infinite, and you will arrive finally to the end of this knowledge where you can contribute to today's science.

== Machine (computer) Input Output ==
1 and 0 are the main aspects of machine level input output. 1 means there is an electrical signal (or there is electricity) and 0 means there is no electrical signal (or there is no electricity).
On this level you get more into the electronic level of the computer. I recommend to study electronics to get a further expertise on this level.

The AC or DC electricity that feeds the computer is the first input of the computer. Then comes the printer, the screen, the audio video. These are some classical outputs that we know. But there are also other computers that are incorporated in cars, in working machines, in washing machines, in cellular phones, on stone cutting machines with laser output etc.
When we consider the mother of today's computer: it was working without electricity, and it was a textile machine that been converted to a machine that gets an input as paper with special holes combined with a special system. So as when you make this input into this textile machine, it could make a calculation and give you the result of this calculation as output.

But the I/O of the machine is not limited to the whole computer. There is also input output on each part of the computer. A hard disk gets input as an electronic signal.
A RAM card also gets input as electronic signal and output as electronic signal.
A chip is also getting an electronic signal and output as another electronic signal
A circuit is also getting an electronic signal and outputs an electronic signal.

So as you can see here you can get smaller and study more and more these electrical signals as input and output.

To analyse these electronic signals you must learn boolean logic, and logic calculation in mathematics. Also, algorithms is related to input and output on electronics.

== Input Output on the coding level ==

On the coding level we can analyse the input and the output by the use of algorithms.
On the coding level not all input produces output. There are five categories of input and output.
* remark type of inputs: no action and no calculation by the computer is done here
* declaring type of inputs: these inputs are preliminary to a calculation. you say here to the computer "Get ready!"
* conditional inputs: the computer is confronted to a choice. this is post preliminary input
* variable inputs: the computer is starting to use a variable, the variable has first value as null and can get on secondary level a value.
* calculation inputs: here the computer is confronted to a calculation. The computer got into this level in the result of declarations, choices, and variable with values. Now it is using these to prepare the output

- Finally the output as an electronic level: all calculations are electrical signals. So the result is at first coded as an electronic signals combination
- output as "input" in the RAM
- Binary output = electronic signal is converted in binary: 1 means there is electricity and 0 means there is no electricity. The combination of these two are converted into 8 or 16 bit values, which means 8 times 0 or 1. For example: 00000000, 11111111, or 10101000, etc.

- The output as machine language = the 8 or 16 bit value converted into machine language
- the output converted to coder language = here the result is in the memory according the programming language used by the coder. Here I suppose the program is using machine language and translates it into the programming language of the coder.

On the next level we will see the output on user level.

== Input Output on end user level ==

Here electricity becomes a letter on the screen, or the move of the arm of a robot, or a laser shot, or a car engine start.

You must consider here that we use computers not only as personal computer but also in our cellular phones, in our televisions, robots, children's toys, trains, airplanes, warhead missiles, etc. Almost everywhere there are computers.

Maybe a fun example comparing to a personal computer will be the simple kitchen robots with many sort of knives to cut and get juice of vegetables and fruits.

The input in kitchen robot is the fruit, and the output is the fruit juice.

In personal computer of the end user, the input is the children age of school in Turkiye Istanbul, and the output will be the average age of these children as displayed on the screen or on the printer.

The input on an iron cutting machine will be the iron cutting style designed in AutoCAD and recorded in the memory of the machine, and the output will be the laser movement so as to cut iron according the project.

The examples here are infinite. We can group inputs here as follows:
* numeric or alphanumeric input as record (see previous lesson about record string and arrays). Example: entry of names, entry of birtdates, entry of age, of number of children etc.
* graphic analog input example: GIF, BMP, JPEG, MPEG
* graphic numeric input example: AutoCAD inputs, Corel Draw and Photoshop as input
* mechanical input. This is for non electrical computers: the paper with holes input in the textile machine
* biochemical input: This is the input done by taking a pill, or DNA changes, etc.
* Mind Input: So far the human brain is the most complex input/output existence on this world. The personal computer is so far just a copy of maybe a microscopic part of our brain. You must never forget that a computer still cannot dream or have psychological disturbance, or create something. So I will place on the highest place and on the center of any study the mind of human and animals.

About the outputs there is also an infinite number of output possibilities. For example:
* numeric or alphanumeric output: example : display on PC screen of the list of children names in Istanbul, Turkey
* graphic analog output: example: JPEG picture
* graphic numeric output: example: AutoCAD screen output of museum plan
* mechanical output: example: flower picture drawn on Iron plate
* biochemical output: example: hormone control operated by pills, AIDS virus being destroyed by microscopic artificial intelligence microrobots in human veins (this project is still in research status, its appliance is limited to animals)
- mind output: example: this whole text is my mind output by the use of my fingers

== Last words about I/O ==

Input/output can be electric or non-electric signals. It can be mechanical, biological or even abstract.
The reason is simply because the computer was first created when there was no electricity, and also because the computer use is now extended in so many areas that it is difficult to say input/output is just about PCs.

A computer scientist is not limited to electrical and electronic devices. In today's world where expertise became a unique way to find a job, it has resulted in limitation on human abilities used. So science has just reached a paradox.
To go out of this paradox, I suggest the following, consider computer not only as electroinic devices, but all.
Today computer scientists act as if the computer is just a PC. What about biomedical or what about industry?
The first computer was created before electricity was created. So the input/output has been invented much more before Edison.

*[[Program design principles|Next lesson]]
*[[Introduction to Computer Science|Back to course contents]]

[[Category:Basics]]
[[Category:Computer science]]