Perpetuum Mobile II
This device, described by Villard de Honnecourt in 1235, is an example of the so-called perpetual motion machine of the first kind—a machine that produces energy from nothing (which is prohibited by the first law of thermodynamics). As the wheel turns, the arms on the left fall over a greater distance than the dangling arms on the right; the difference in torque causes the wheel to turn.
For more about perpetual motion machines see "Perpetual Motion" on Wikipedia.
"Perpetuum Mobile II"
Wolfram Demonstrations Project
Published: March 7 2011