The black block is a high-temperature superconducting material. The silver
disk is a strong magnet. When the superconductor is cooled with liquid
nitrogen and becomes superconduction, any movement of the magnet generates
an opposing eddy current in the superconductor. By Lenz's law, this eddy
current produces an opposing magnetic field that opposes any movement of the
magnet. Since there is no resistive loss in the superconductor, the magnet
just stays where it is left.

--
Bob (Chief Pilot, White Knuckle Airways)


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http://www.metacafe.com/watch/55826/..._explain_this/