Newton's Cradle is the popular name for a device consisting of a row of incompressible (usually steel) spheres, each of which hangs from a frame by two wires in such a way that the row of balls are in contact with one another at rest. When one ball is pulled away then allowed to swing back and strike the end of the row, the ball at the far end of the row acquires the momentum of the first ball while the others remain at rest. This will continue back and forth with a pendulum-like action until the initial energy is dissipated as heat and sound.

Newton's Cradle is a popular desktop toy, and also serves to demonstrate conservation of momentum.