http://en.wikipedia.org/wiki/Eddy_current_brake http://en.wikipedia.org/wiki/Eddy_current_brake You can get clever with pulsed electromagnets and active coils,

http://en.wikipedia.org/wiki/Eddy_current_brake http://en.wikipedia.org/wiki/Eddy_current_brake You can get clever with pulsed electromagnets and active coils, but eddy current braking works just fine with a permanent magnet and a thick piece of copper: http://www.youtube.com/watch?v=nrw-i5Ku0mI http://www.youtube.com/watch?v=nrw-i5Ku0mI