Demos: 1N-16 Happy Sad Balls
These two rubber balls which are similar in appearance are really quite different. The major difference is a quantity known as hysteresis, which is the natural tendency of the rubber to return to its original shape after deformation. One ball is quite low in hysteresis (made out of a conventional neoprene rubber) while the other ball is high in hysteresis (made from a rubber compound called Norsorex). Drop the balls from the same height and the one with the lower hysteresis will rebound much higher than the other ball (in fact the low hysteresis ball will hardly bounce at all). Also as an additional demonstration, you can roll both balls down an incline plane and they will reach the bottom at different times. This is due to the fact that the rubber that makes up the balls has different coefficients of friction. The happy ball exhibits lower surface friction than the sad ball which causes it to roll more rapidly.