If you take two circular magnets and slap them on the ends of a AA battery, the resulting axel will drive on a road of aluminum foil. This is called a homopolar motor and it’s one of the simplest machines you can build. How does it work? Well, it’s been awhile since my last electromagnetism class, but the homopolar motor works because the combination of the flow of the electric current (from the battery) and the flow of the magnetic current produces a torque via the Lorenz force. This short video explanation should give you a good idea of the principles involved. (via digg)