In a collision:<\/p>\n\n\n\n
Collisions are categorized by what happens to the total kinetic energy of the system. In an inelastic<\/em> collision, the total kinetic energy is different before and after the collision. In an elastic<\/em> collision, the total kinetic energy is the same before and after the collision.<\/p>\n\n\n\n On the scale of macroscopic objects, all collisions are inelastic. However, some are very close to elastic. For example, a collision between two pool balls is very nearly elastic. On the atomic and subatomic scale, collisions that are truly elastic occur regularly.<\/p>\n\n\n\n Collisions in which objects permanently change shape (deform) are very common examples of inelastic collisions. Energy is required for deformation\u2014this energy is provided by the kinetic energy the objects had before the collision.<\/p>\n\n\n\n Momentum is conserved (as in all collisions):<\/p>\n\n\n\n pi<\/sub><\/em> = pf<\/sub><\/em><\/p>\n\n\n\n but kinetic energy is different before and after:<\/p>\n\n\n\n Ki<\/sub><\/em> \u2260 Kf<\/sub><\/em><\/p>\n\n\n\n As a special case of this, consider two objects that stick together after a collision. For two objects to stick together, there is generally some sort of deformation involved. When two objects stick together, it is often called a perfectly<\/em> or completely<\/em> inelastic collision.<\/p>\n\n\n\n However, objects do not need<\/em> to stick together for the collision to be classified as inelastic. For example, a rock flying through and shattering a class window would be an inelastic collision: when the glass shatters, chemical bonds are broken, which requires energy. The energy required to break the glass comes from the kinetic energy of the rock.<\/p>\n\n\n\n7.2.1 Inelastic collisions<\/h3>\n\n\n\n
Example<\/h4>\n\n\n\n\n