Happy/Sad Ball Set, 1 Each

United Scientific® Happy/Sad Ball Set by United Scientific is a pair of black rubber balls, each 1-3/8 in. in diameter, that look and weigh the same but are made from different rubbers. Dropped from equal heights onto a hard surface, the happy ball bounces high and the sad ball barely bounces, and the happy ball also rolls faster. Science teachers use the set to open lessons on elasticity, kinetic energy, and polymer composition.