| Description: |
A small magnet is attached with tape to the end of a flexible, plastic
ruler. It is held just above a metal disk which can be set into rotation by a
turntable. As the disk speeds up, the magnet is first pulled (mostly) in the
direction of the disk's motion underneath the magnet. This is due to the
friction drag force. Then at higher speeds the magnet is also noticeably pushed
upwards away from the disk. This is due to the levitation force. Both of these
forces arise from eddy currents induced in the metal disk as a consequence of
Lenz's law. If the magnet is moving above but parallel to a flat conductor, the
ensuing magnetic levitation at higher speeds has been studied as a novel way to
move trains. |