The physics toy Newton made is called "Newton's cradle" and is also called "colliding balls", "Newton's spheres", "counting balls", "impact balls", "ball-chain", the "executive pacifier", and even, believe it or not, "Newton's balls."When the ball on one end is pulled aside and allowed to swing as a pendulum, it hits the next ball. But the outcome is fascinating, the one ball on the far end is knocked away from the others with the same speed as the first ball had initially and all of the other balls remain nearly at rest. If you pull back two balls and let them strike the others, two balls are knocked from the other end, and all the other balls remain nearly at rest. Why does this happen? Why are these the only outcomes that occur? Why not others? This happens because: When a ball is lifted, it is given potential energy. When it is dropped, it is given kinetic energy. This kinetic energy is passed on through the balls and given to the last ball which rises and the cycle starts all over again. If you do not own a Newton's cradle, then please play with this interactive flash animationdemonstrating the behavior of this toy. For more information go to http://www.lhup.edu/~dsimanek/scenario/cradle.htm.