Part 1 of Essay
When two objects collide, their motions are changed as a result of the collision, as is shown when playing pool. There are several laws governing collisions, the principal one being the law of conservation of linear momentum, which says the total momentum of an isolated system is the table and the balls, and the law then i ....

Part 2 of Essay
.... the relative velocities of the two objects are the same before and after impact, the coefficient is equal to 1, and the collision is elastic. In practice, however, such perfectly elastic collisions occur only on an atomic scale; most collisions are therefor not elastic, with a coefficient of restitution of less than 1. ....