This cradle 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 only as a result of friction an interesting process to watch; Bring this quirky desk toy and a bit of unprecedented genius into your life for a daily dose of inspiration; The contact of the outer ball with the inner balls of Newton's Cradle has the visually startling effect of moving all the energy through the stationary balls so that only the outer balls move; It's curious to watch and may well have you mesmerised for hours. But hey! The Newton's cradle wasn't only a tool used by the great brainy man himself to prove a sceintific point it is also a fantastically relaxing object to have ticking and clicking away at your elbow as you work rest or play. Have one in your life today and see if you can't steal a bit of sparking intelligence too. Model H51S Quantity 1 piece(s) per pack Color Red brown + silver Material PVC + stainless steel + fishing line Specification This classic desktop display piece has become a must have for office decor; Swing one steel marble back let it go and watch as kinetic energy causes the one on the opposite side to swing the same distance; If youre feeling saucy one day try swinging two or three at once- just dont pass out from the excitement! Suitable Age 8 years old above Packing List 1 x Balance balls