![Newton's cradle](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/Newtons_cradle_animation_book_2.gif/300px-Newtons_cradle_animation_book_2.gif)
Newton's cradle, named after Sir Isaac Newton, is a device that demonstrates conservation of momentum and energy via a series of swinging spheres. When one on the end is lifted and released, the resulting force travels through the line and pushes the last one upward.