Newton's Cradle is a clever device that uses a series of equal pendulums in a row to demonstrate the Laws of Conservation of Momentum and Conservation of Energy.

By pulling one ball away from the others and releasing it, the ball will swing and strike the second ball, which in turns sends the momentum through the series of balls causing the last ball to move away from the group. When the last ball swings back, its collision then causes the first ball to move away. This process repeats until it finally wears down. Pulling away several balls will result in the same number of balls moving away at the other end.