Eddy Current Levitation

What it shows:

It's impossible to magnetically levitate an object with static magnetic fields. However, it's posible to levitate a magnet with another hand-held magnet by taking advantage of eddy currents.

How it works:

A rectangular block of copper (6"×6"×2") is stacked on top of another one (6"×6"×1"). They are separated by 1" plastic spacers. A rectangular bar magnet (2"×2"×½") is placed in the space between them. When a second magnet is lowered from above, the two magnets attact each other. However, rather than "jumping up" toward the second magnet, the bar magnet rises slowly. This is due to the generation of strong eddy currents in the copper blocks — sudden motions of the magnet would induce large eddy currents that, in turn, damp the motion by the Lorentz force interaction. Observing the bar magnet rising slowly provides visual feedback to the person holding the second magnet and the long time constant gives the person time to raise the hand-held magnet higher, thereby decreasing the mutual attraction between the two magnets. This results in the suspended magnet to start to fall slowly but, again, the person has ample time to make adjustments and have it rise again. With just a little practice, the person can levitate the magnet suspended between the two blocks of copper! Although the magnetic fields are static, the levitation process is not. Feedback combined with a long time constant allows the person to make continuous small adjustments. Call it quasi-static.