# Lorentz force in homopolar motor

There are a lot of videos showing the simple homopolar motors in action. Let's look at this one: http://www.youtube.com/watch?v=6jyraFLqfqE It is supposed to be working due to the Lorentz force.

Electrons go through the magnet, deflect under magnetic field due to the Lorentz force and colliding with atoms in the magnet, rotate it.

But what if electrons would travel not through the magnet itself but through the thin wire put between the battery and the magnet, directly connecting + and - of the battery. In this way electrons would still travel in the same direction in same magnetic field, but in the thin wire, not in the magnet. Would then the magnet rotate?

Now the other video: http://www.youtube.com/watch?NR=1&v=zOdboRYf1hM&feature=fvwp Here electrons travel through the wire but still close to the magnet so we still can assume that electrons are deflected due to the Lorentz force even though magnetic field should be weaker on the side of the magnet.

But what would happen if everything would be glued together: battery, magnet, wire. Would then this system rotate? While the electrons would still travel under the magnetic field they should be deflected and rotate the whole system. But it sounds unphysical. Can somebody explain how it works?

-
If the whole thing was levitating, I don't see why it couldn't rotate. Its simply a device that transfers electric potential energy (the battery) into kinetic rotational energy. It doesn't rotate for 'free', it needs to battery's energy. This is no different from a bomb being able to explode on its own. Transfer some inner potential energy to whatever, by whatever mechanism. In this case the device is made such to provide the magnetic scaffoldings to make itself spin with Lorentz force – Mathusalem Jul 14 '13 at 22:09