K2-46
Demonstrate Lenz's law in a dramatic way.
A small rare-earth magnet is glued onto a short plastic strip, and held above a rapidly spinning aluminum disc. Eddy currents in the disc create a magnetic field which levitates the magnet. Let the magnet hang loosely on the disc at rest, then start the rotator.

Note: When using, be careful to avoid the center of the spinning disc. The axle is steel, which causes a very different result in a magnetic field!