20. Coefficient of Restitution

Various balls are dropped in a transparent tube to show nearly elastic, partially inelastic, and totally inelastic collisions. The height of the bounce, marked off qualitatively on the tube, is a measure of the elasticity. A lead ball which does not bounce at all is startling.

With another piece of apparatus a small steel ball is dropped on a heavy, polished, slightly concave steel plate. The collisions are so elastic that the ball bounces dozens of times before its energy is exhausted.