# Q & A: magnets driving a rotor?

Most recent answer: 02/10/2015
Q:
would it be possible to arrange a ring of magnets that would repel two magnets mounted on a rotor causing circular motion
- Robbie
UK
A:

No. The potential energy of the interaction between the two sets of magnets will be some function of the angular position of the rotor. If it happens to start at a minimum, it will stay at that minimum. If it starts on a slope, it will turn downhill, converting potential to kinetic energy, then go partway back up the angular hill, roll back down, etc. You could extract a little energy, leaving the rotor sitting at the minimum energy position, the bottom of the hill.

If the rotor starts exactly at the top of the highest hill, then if something gave it a tiny push one way or the other it could keep rotating, if we ignore friction. If you extract a little energy, then it can't make it back over the hill and will stop rotation, just like the case we discussed where it starts partway up.

Mike W.

(published on 02/10/2015)