An interactive toy demonstrating the conservation of momentum.
The Newton's Cradle animation lets you play online with this toy. The cradle consists of a number of balls in a line - as many as you choose - all hanging from strings. The balls can be pushed or pulled sideways and released so that they knock against each other. Balls hitting at one end of the cradle cause movement of the balls at the opposite end. This is a demonstration of momentum being transferred and so conserved.