# How to figure out the magnets needed to repulse a given weight?

Given a weight. Is it possible to determine what strength of magnet and what width, length and thickness would be needed in order to repulse that weight a given height? If so, how?

To be clear:

Two magnets, one on top of the other, repulsing.

||=========||
^^^^air^^^^
||=========||

Now I'll place an object of a certain weight on top.

I want the object to float in mid air at a certain height.

I am trying to figure out how to calculate what strength magnet I'd need in order to make the object float at a given height, given a weight of said object. Pick any type of magnet.

-

Given a weight

Knowing the weight is not enough. Each material has its own magnetic susceptibility, which can even be a tensor for a crystal. We would need to know the weight and the magnetic susceptiblity to know how the material would behave in a given magnetic field.

For example diamagnetic materials experience a force in a direction of decreasing field strength, while paramagnetic materials experience a force in a direction of increasing field strength.

Is it possible to determine what strength of magnet

It is not just a matter of the strength of magnetic field. The gradient of the magnetic field matters.

For the edited version of the question asking about the force between two magnets, Wikipedia has equations for various shapes of magnets at the above link. The force from those equations must exceed the gravitational force (weight) for levitation.

-
I edited my question above for clarification. – Johnston May 16 '14 at 14:29
– DavePhD May 16 '14 at 14:48