I built this DC Motor I found here
Its essentially a coil with a magnet connected to a battery. So we built it and it worked.
The main question is, why? I thought that the motor had to have a brush or something to change the direction of the magnet or the coil. Without it, the torque would change to the opposite direction once it flipped over, and I would expect a sort of wobbling motion. My friend thought it would be something to do with the change in flux and inducing magnetic fields, but according the Lenz's law, this should not produce a continous motion because the induced magnetic field will always try to oppose motion.
Why does it keep spinning?
(On a side note, it stopped working when we disconnected it from a small battery and changed to a bigger DC source. If anybody could maybe explain this too that would be nice.)
OK, so we didn't actually build it right. We more or less just looked at the pictures, pretended we knew what we were doing and improvised. We missed the crucial step of shaving only half of the plastic off of the wire. The strange part is that it was working even though we didn't do this step. Is there any explanation as to why this works even though we missed that step?