A Homopolar motor is a simple motor, consisting of three parts, a magnet, a regular sized battery, and a strip of copper wire..
the magnet is put on the bottom of the battery, and the wire is shaped in a way so a part is on the magnet and the top of the battery
when one releases the hand, the metal strip spins rapidly...
i believe it is one of the simplest motors you can build
hold on i'll find a video
oh and i didnt google that, I ACTUALLY KNEW IT... VERY NICE!!
http://spikedhumor.com/articles/90173/Homopolar_Motor.html