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Archive:In statics, the sum of the forces is equal to zero

2007-06-17T02:35:32Z

70.121.98.26:

Lesson:In Statics the Sum of the Forces is Equal to Zero

The term statics refers to an object or system in static equilibrium. The object or system is motionless because all of the forces balance to zero.

Newton's Second Law:

Σ<math>F = ma</math>

The sum of the forces is equal to the mass times the acceleration. The 2nd law tells us that if the object or system is motionless, the acceleration is equal to zero. Therefore the sum of the vector forces must be equal to zero.

Example: Consider a table with four legs and a 200kg object resting motionless in the center of the table.

Object 200
______________
| | Weight of table = 100kg
| |
| | What is the force acting up on each table leg?

Then the force upward on the legs is found by balancing these forces in the equation given by Newton's Law:

sum F=MA = 0 = - (200kg X 9.81 m/s2) - (100kg X 9.81 m/s2) + (Forceleg X 4)

Gravity is acting down on the 200kg object and the 100kg table.

Forceleg = ((200kg X 9.81 m/s2) + (100kg X 9.81 m/s2)) / 4

The units kg•m/s2 are equivalent to the units N/kg. Thus when multiplying through, the kilograms cancel out.

Forceleg = (1962 N + 981 N) / 4

Forceleg = 735.75 N

Notice that it is critical that a consisent sign convention is followed throughout an entire analysis effort. The sign convention is typically chosen in more complex problems to ease the total amount of algebra necessary to analyze the equations in the x, y, and z axis.

[[Category:Engineering]]
[[Category:Statics]]

Supply tower

2007-06-01T03:20:13Z

70.121.115.224:

A '''supply tower''' (sometimes erroniously called a [[launch tower]]) is constructed on the [[launch pad]] of a [[rocket]] to facilitate fueling and loading cargo into the craft. A supply tower also usually includes an [[elevator]] which allows maintenance to be performed and, in the case of a manned penis rocket, the crew to board. Immediately before ignition of the rocket's motors all connections between the tower and the craft are severed and the bridges over which these connections pass often swing away to prevent damage. In contrast with launch towers, supply towers do not guide rockets as they lift off.

{{Rocket-stub}}

[[Category:Rocketry|Supply tower]]

[[de:Versorgungsturm]]

Precipitation (chemistry)

2007-02-07T21:30:27Z

70.121.204.143: /* Cation sensitivity */

: ''"Precipitate" redirects here, for the [[Interpol (band)|Interpol]] [[Extended play|EP]] see [[Precipitate (EP)]].''

'''Precipitation''' is the formation of a [[solid]] in a [[solution]] during a [[chemical reaction]]. When the chemical reaction occurs the solid formed is called the '''precipitate'''. This can occur when an insoluble substance, the '''precipitate''', is formed in the solution due to a reaction or when the solution has been [[supersaturated]] by a compound. The formation of a precipitate is a sign of a chemical change. In most situations, the solid forms ("falls") out of the solute phase, and sinks to the bottom of the solution (though it will float if it is less dense than the solvent, or form a [[suspension (chemistry)|suspension]]).

A use for this type of reaction is when making paints.

This effect is useful in many industrial and scientific applications whereby a chemical reaction may produce a solid that can be collected from the solution by various methods (e.g. filtration, decanting, centrifuging). Precipitation from a [[solid solution]] is also a useful way to [[precipitation strengthening|strengthen]] [[alloy]]s, this process is known as [[solid solution strengthening]].

An important stage of the precipitation process is the onset of [[nucleation]]. The creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative [[surface energy]] of the solid and the solution. If this energy is not available, and no suitable nucleation surface is available, [[supersaturation]] occurs.

An example of a precipitation reaction: Aqueous silver nitrate (AgNO3) is added to a solution containing potassium chloride (KCl) and the precipitation of a white solid, silver chloride is observed. (Zumdahl, 2005)

:AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

The silver chloride(AgCl) has formed a solid, which is observed as a precipitate.

This reaction can be written emphasizing the dissociated ions in a combined solution
:Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(solid) + K+(aq) + NO3-(aq)

A final way to represent a precipitate reaction is known as a ''net ionic reaction''. In this case, any spectator ions (those which do not contribute to the reaction) are left out of the formula completely. This simplifies the above equations to the following:
:Ag+(aq) + Cl-(aq) → AgCl(s)

==Cation sensitivity==
Precipitate formation is useful in the detection of the type of [[cation]] in an unknown [[salt]]. To do this, an [[alkali]] first reacts with the unknown salt to produce a precipitate which is the hydroxide of the unknown salt.

To identify the cation, the colour of the precipitate and its solubility in excess are noted.

Similar processes are often used to separate chemically similar elements, such as the [[rare earth]] metals.

==Reference==

Zumdahl, Steven S. ''Chemical Principles.'' 4th ed. New York: Houghton Mifflin Company, 2005.

==External links==
* http://www.hci.edu.sg/~limth/lessons/2002/qa/cations.htm
* [http://www.hielscher.com/ultrasonics/precipitation_01.htm Continuous Precipitation Using Ultrasonication (e.g. for nano-size magnetite particles)]

==Literature==

Banert, T., Brenner, G., Peuker, U. A. (2006), Operating parameters of a continuous sono-chemical precipitation reactor, Proc. 5. WCPT, Orlando Fl., 23.-27. April 2006.

[[Category:Chemical processes]]

[[de:Fällungsreaktion]]
[[es:Precipitado]]
[[fr:Précipité]]
[[he:תגובת שיקוע]]
[[nl:Neerslag (scheikunde)]]
[[ja:沈殿]]
[[no:Fellingsreaksjon]]
[[nn:Fellingsreaksjon]]
[[pt:Precipitação (química)]]
[[ru:Преципитат (химия)]]
[[sv:Utfällning]]
[[zh:沉淀]]

Precipitation (chemistry)

2007-02-07T21:29:35Z

70.121.204.143: /* Cation sensitivity */

: ''"Precipitate" redirects here, for the [[Interpol (band)|Interpol]] [[Extended play|EP]] see [[Precipitate (EP)]].''

'''Precipitation''' is the formation of a [[solid]] in a [[solution]] during a [[chemical reaction]]. When the chemical reaction occurs the solid formed is called the '''precipitate'''. This can occur when an insoluble substance, the '''precipitate''', is formed in the solution due to a reaction or when the solution has been [[supersaturated]] by a compound. The formation of a precipitate is a sign of a chemical change. In most situations, the solid forms ("falls") out of the solute phase, and sinks to the bottom of the solution (though it will float if it is less dense than the solvent, or form a [[suspension (chemistry)|suspension]]).

A use for this type of reaction is when making paints.

This effect is useful in many industrial and scientific applications whereby a chemical reaction may produce a solid that can be collected from the solution by various methods (e.g. filtration, decanting, centrifuging). Precipitation from a [[solid solution]] is also a useful way to [[precipitation strengthening|strengthen]] [[alloy]]s, this process is known as [[solid solution strengthening]].

An important stage of the precipitation process is the onset of [[nucleation]]. The creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative [[surface energy]] of the solid and the solution. If this energy is not available, and no suitable nucleation surface is available, [[supersaturation]] occurs.

An example of a precipitation reaction: Aqueous silver nitrate (AgNO3) is added to a solution containing potassium chloride (KCl) and the precipitation of a white solid, silver chloride is observed. (Zumdahl, 2005)

:AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

The silver chloride(AgCl) has formed a solid, which is observed as a precipitate.

This reaction can be written emphasizing the dissociated ions in a combined solution
:Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(solid) + K+(aq) + NO3-(aq)

A final way to represent a precipitate reaction is known as a ''net ionic reaction''. In this case, any spectator ions (those which do not contribute to the reaction) are left out of the formula completely. This simplifies the above equations to the following:
:Ag+(aq) + Cl-(aq) → AgCl(s)

==Cation sensitivity==
Precipitate formation is useful in the detection of the type of [[cation]] in an unknown [[salt]]. To do this, an [[alkali]] first reacts with the unknown salt to produce a precipitate which is the hydroxide of the unknown salt.

To identify the cation, the colour of the precipitate and its solubility in excess are noted.

Similar processes are often used to separate chemically similar elements, such as the [[rare earth]] metals.

Ugh

==Reference==

Zumdahl, Steven S. ''Chemical Principles.'' 4th ed. New York: Houghton Mifflin Company, 2005.

==External links==
* http://www.hci.edu.sg/~limth/lessons/2002/qa/cations.htm
* [http://www.hielscher.com/ultrasonics/precipitation_01.htm Continuous Precipitation Using Ultrasonication (e.g. for nano-size magnetite particles)]

==Literature==

Banert, T., Brenner, G., Peuker, U. A. (2006), Operating parameters of a continuous sono-chemical precipitation reactor, Proc. 5. WCPT, Orlando Fl., 23.-27. April 2006.

[[Category:Chemical processes]]

[[de:Fällungsreaktion]]
[[es:Precipitado]]
[[fr:Précipité]]
[[he:תגובת שיקוע]]
[[nl:Neerslag (scheikunde)]]
[[ja:沈殿]]
[[no:Fellingsreaksjon]]
[[nn:Fellingsreaksjon]]
[[pt:Precipitação (química)]]
[[ru:Преципитат (химия)]]
[[sv:Utfällning]]
[[zh:沉淀]]