2.8 Elastic and Inelastic Collisions
When a tennis ball is dropped on the floor vertically, it may not rebound to its initial height. It is because, a portion of K.E. is lost, partly due to friction as the molecules in the ball move past one another when the ball distorts and partly due to its change into heat and sound energies. Similar is the case when two tennis balls collide with certain velocities, their final kinetic energy may be less than the total initial kinetic energy.
A collision in which the K.E. of the system is not conserved, is called inelastic collision.
Under certain special conditions, no kinetic energy is lost in the collision or impact on hitting the floor. Such type of collision is said to be elastic collision.
For example, when a hard ball is dropped onto a marble floor, it rebounds to very nearly the initial height. It loses negligible amount of energy in the collision with the floor. It is to be noted that momentum and total energy are conserved in all types of collisions. However, the K.E. is conserved only if it is an elastic collision.