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Elastic collisions are collisions in which there is no loss of kinetic energy. Under normal conditions most objects undergo inelastic collisions. These are collisions in which the kinetic energy of the system diminishes after each collision. Bouncing a rubber ball is an example of an inelastic collision. If the ball is dropped, it will bounce several times. After each bounce it never returns to its original height. Each time it bounces, some kinetic energy is lost. It stops bouncing when all kinetic energy is gone. At this point, the only energy left in the system is potential energy. |
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If an object were to undergo elastic collisions, then the kinetic energy of the system will be maintained. Elastic collisions involving a bouncing object such as a ball will cause the ball to always return to the point from which it was dropped. Curiously, the harder an object is, the closer the collisions approximate truly elastic collisions. A steel ball dropped on a steel plate will be very close to an elastic collision. A golf ball bounces so well because it is so hard. |
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It is essential for gas particles to undergo elastic collisions. The total kinetic energy of the system must be maintained. If it is not maintained, then the kinetic energy of the system will drop to zero. Once it reaches zero kinetic energy, then the system has dropped to absolute zero. Experience has shown that a gas phase system will not spontaneously cool if isolated from its environment. It will only cool as a result of losing kinetic energy to the environment. To be true to observed behavior, the Kinetic Molecular Theory must require the Ideal Gas to undergo elastic collisions. While the gas phase system undergoes elastic collisions, it is possible for the distribution of the kinetic energy in the system to change. That is, some objects can gain kinetic energy, but only if others lose kinetic energy. The important point is that the TOTAL kinetic energy of the system remains constant. The kinetic energy of a system is redistributed much like the way pool balls will redistribute kinetic energy. The kinetic energy is redistributed according to the angles at which the objects collide. If a cue ball just barely cuts a ball into a side pocket, that ball rolls at an angle, but ever so slowly. Gas particles behave the same way. As they travel randomly through space, they collide with one another at many different angles. These random collisions cause objects to always be changing their speed, and kinetic energy. |
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In conclusion, the total kinetic energy of a gas phase system remains constant as long as the system is not heated or cooled by some outside factor. Provided that no gas particles are added or taken away then the average kinetic energy of the system will also remain constant. Therefore, the temperature of the system remains constant. |
