Newton’s Cradle

Newton's Cradle is a device consisting of a series of balls placed on strings or wires, suspended from a frame. The balls are arranged in such a way that when one of them is lifted and released into motion, gravity causes it to strike the nearest ball, transferring kinetic energy which propagates through the balls along the strings. This process causes the last ball to swing out and then return to its original position. This device demonstrates the principle of conservation of momentum and energy, showing that energy can be transferred from one ball to another without loss.

My interpretation of the model found on the web (link in the description).