Eddy currents: Copper disk rotates over a spinning bar magnet.

Eddy currents: Copper disk rotates over a spinning bar magnet. Turning the handle of the 'rotator' causes the strong Alnico magnet to spin rapidly beneath the copper disk. The changing magnetic flux from the magnet causes eddy currents in the copper. The eddy currents create magnetic fields that drag against the bar magnet. The net effect is that the copper disk starts to rotate in whatever direction the bar magnet is rotating