A series of experiments with magnets, aluminum cans and othere parts and pieces.
This experiments turn around the eddy currents. That currents are induced by a changing magnetic field near a metal electrical conductor. That currents generate a magnetic field opposed to the first one that brakes and drags the magnet-conductor system.
http://en.wikipedia.org/wiki/Eddy_current http://en.wikipedia.org/wiki/Electromagnetic_induction http://en.wikipedia.org/wiki/Metal_detector http://en.wikipedia.org/wiki/Inductive_sensor http://en.wikipedia.org/wiki/Electrical_conductor http://en.wikipedia.org/wiki/Induction_heating http://en.wikipedia.org/wiki/Eddy-current_testing