Doubochinski's pendulum

Doubochinski's pendulum is an experiment with an oscillator and a magnet. The most simple case is that of a pendulum that interacts with an oscillator. The pendulum (with a magnet at the end) will swing at a frequency of one swing per period of 1-2 seconds. A stationary electromagnet is placed under the equilibrium point of the pendulum. The electromagnet is then supplied with an alternating current of a fixed frequency, of between 10 and 10.000 Hz. 
When the pendulum is released at any location, its movement will then evolve to stop at a height which depends on the frequency of the current of the electromagnet. This phenomenon was first discovered by the brothers Danil and Yakov Doubochinski in 1968–69.