You can build one of these perpetual motion machines and amaze your friends

Place a metal ball on the white circular track and watch it go around and around with no visible means of force. How does it work? Inventor Greg Zumwalt reveals the secret at Instructables, where he also shows you how to build one of your own:

To overcome gravity and those thermodynamic law things, I've hidden an infrared transceiver, an electromagnetic coil and some electronic circuitry in the base to accelerate the ball bearing up the hill.