Small Newton Pendulum with Steel Balls and Wood Base This Newton’s Cradle or Newton’s Pendulum demonstrates Newton's principle that 'action and reaction are equal and opposite'. If one of the steel balls is lifted and allowed to fall back at one end, then one will swing out the same distance at the other end. This causes the beginning of perpetual motion which dies down as a result of air friction and suspending wires lost, elastic deformation (warping) of the balls and sound… an interesting process to watch. Steel balls diameter: 12mm. Dimensions: 90 x 76 x 91 mm