Investigate conservation of mechanical energy and momentum with this intriguing device. The wheel is rolled to the top by means of nylon strings wound on its axle. When released, its potential energy becomes kinetic, allowing it to roll back down. At the bottom, kinetic energy is converted into potential and the wheel rolls upward again. In an ideal world this would continue forever, but friction eventually sets in and the wheel will stop.  Size, 44 x 29cm.