M-EngMom18: Energy stored in a rubber hemisphere.
 
PIRA: Unknown 

Equipment: half of a rubber ball (the hemisphere of a racquet ball perhaps) found in Set 9, Cabinet 2.

Procedure: The transformation of elastic potential energy to kinetic energy is shown by the extreme height to which a hollow rubber hemisphere jumps when it is turned inside out and dropped from about waist high.

Because of its initial curvature in manufacture, a hollow rubber hemisphere that is turned inside out stores a lot of energy. You can easily see this by popping the hemisphere from one equilibrium configuration to the other, and seeing that one popping direction is a lot more vigorous than the other. When the inside-out hemisphere is dropped it pops into the lower-energy configuration with a gain of kinetic energy.

Turn the hemisphere inside out, drop from waist height so that it falls on its flat side and the hemisphere will rebound to great height.