# Why doesn't it just flip over

1. Mar 26, 2009

### Forestman

With normal magnetic objects if you try to make one levitate above the other, it will just flip over and stick to the other magnet. Why does this not happen when using a superconductor. Why is a magnet able to levitate above a superconductor without flipping over to the opposite poll.

2. Mar 26, 2009

### alxm

The magnet and superconductor repel due to the Meissner effect, not due to the the superconductor being a magnet.

A weak (attractive) magnetism is induced due to inhomogeneities in the superconductor, which leads to the the attractive force holding the magnet in place.

3. Mar 26, 2009

### nbo10

uhh no.

It's due to flux pinning effects.

4. Mar 26, 2009

### phz

In a way alxm is describing the flux pinning effect. I don't intuitively see it as an attractive force, more as just a local potential energy minimum for the system when the field lines line up. A small movement by either object would make the field lines want to bend close to the the boundaries if the superconductor to still line up, thus the curvature of the lines would increase which is equal to a higher energy state. Therefore it will require an external force to move either the magnet or the superconductor.

To address the original question: the superconductor is not a magnet in the same way, the flux pinning effect merely "freezes" the magnetic field lines in a certain configuration inside the superconductor (because of inhomogeneities in the superconductor). It will be more desirable for the magnet to have its field lines line up with the ones frozen in the superconductor, therefore it will strive to stay in the place it was when the field lines where frozen (when the superconductor entered its superconducting phase).

If you have a magnet levitating above another, then it will flip over since the system is in an unstable equilibrium. The levitating state is at a stationary point, but not at a local potential energy minimum. A tiny perturberation of the system will make it "roll down the potential hill" by flipping over and reaching a lower energy state.

5. Mar 26, 2009

### Forestman

Thanks phz, I understand it now. I also watched a video on You Tube about it, and that really helped.