'Happy' and 'Sad' Balls

Vividly demonstrate elastic and inelastic collisions.

Although both balls are identical in shape, the "happy" ball rebounds very well while the "sad" or "unhappy" ball does not. Several experiments involving the simple bounce and roll of these balls demonstrate repulsion and inelasticity. When dropped on a hard surface from an equal height, the happy ball bounces high and the sad ball barely bounces at all. The happy ball also rolls faster than the sad ball. These balls provide an interesting and memorable demonstration for studying elasticity, kinetic energy, and polymer composition.