# Energy conversion question

1. Apr 28, 2010

### CuriousGorge

New here. If this isn't the right forum for the question excuse me.

I saw a science demonstration of converting heat to mechanical energy. it was a circular rim supported on an axle by rubber band spokes, kind of like a bicycle wheel but with rubber bands instead of metal spokes. kind a a science fair demonstration sort of thing. So you shine a heat lamp on one side of it and the bands shrink from the heat throwing it off balance and it spins.

supose you glued magnets around the rim with all like poles facing out and place another magnet near the rim so it repells the wheel off axis. Why wouldnt that work? how would that be different from the heat transfer?

2. Apr 28, 2010

### LostConjugate

Well for one magnets are not a very good source of heat.

I can't picture your example, though you could cause a wheel to spin with magnets, however if you did this would no longer be an example of heat to mechanical energy conversion.

3. Apr 28, 2010

### Staff: Mentor

Because magnets don't just repel, they also attract.

4. Apr 29, 2010

### CuriousGorge

I realize of course the magnet version would be a perpetual motion and we all know that is impossible. The laws of physics forbid it. Most such ideas it's easy to see where they break down but with this idea I just cant see where it is different from the heat version. I guess what I was looking for is an explanation of how the attraction counteracts the repulsion and makes it not work. Because just from my thought experiment point of view both version look the same. the rim being offset from the axel either by contracting bands or by magnetic repulsion. I'm not smart enough in math and geometry to figure out the energy vectors.