# Calculating the froce between two magnets

1. Oct 22, 2005

### chui

I have a formula, taken from Wikipedia:
"http://en.wikipedia.org/wiki/Magnet#Calculating_the_Magnetic_Force" [Broken]

But I didnt get the meaning of "mu" in this formula..
can anyone explain?

Last edited by a moderator: Apr 21, 2017 at 9:05 PM
2. Oct 22, 2005

### Integral

Staff Emeritus
$$\mu$$ is the permeability of the medium between the magnets, in your case this is probably air, the value of [itex] \mu_{air} \approx \mu_0 = 1.26 x 10^{-4} \frac {Henry} {meter} [/tex].

Last edited by a moderator: Apr 21, 2017 at 9:05 PM
3. Oct 22, 2005

### pervect

Staff Emeritus
Another thing that's worth pointing out is that magnetic poles (aka monopoles) have never been observed to exist, though theoretically they may have existed at very early times in the formation of the universe.

So if you want to calculate the force between a pair of real magnets like the kind you'll be likely to find on your refrigeratior, you'll need to work out the force between dipoles, not magnetic poles (aka monoples). This will lead to a much more complex formula, and a non-inverse square relationship for the force.

Modeling a magnetic dipole as a pair of magnetic poles some distance will be very useful in calculating the force between real magnets, but as far as real-life applicaitons go, the wikipedia formula has only done half the job.

4. Oct 22, 2005

### chui

no mass?

Well, Does this force not effected by the magnet Mass?! (unlike gravity etc.)
why is that?

5. Oct 22, 2005

### pervect

Staff Emeritus
The electric force between two charges depends on the charge, not the mass. The magnetic force is basically a relativistic correction to the electric force, so it depends on charge and velocity (i.e. current).