Conservation of Momentum and Kinetic Energy (Newton's Cradle)

Newton's cradle is a device, usually made of metal, that demonstrates the principles of conservation of momentum and conservation of energy in physics with swinging spheres.

When one sphere at the end is lifted and released, it strikes the stationary spheres, compressing them and thereby transmitting a pressure wave through the stationary spheres, which creates a force that pushes the last sphere upward. The last sphere swings back and strikes the stationary spheres, repeating the effect in the opposite direction. The cradle thus demonstrates conservation of momentum and energy.

The large version is more visible in a large room, but the small version works better -- the steel balls are more "elastic"