# How can I produce a net translational force on a ferromagnet?

1. Mar 15, 2004

### endersdouble

How can I produce a net translational force on a ferromagnet?

2. Mar 16, 2004

### Palpatine

I think thats analogous to asking how you balance an egg on the tip of a pen.

3. Mar 16, 2004

### Integral

Staff Emeritus
Re: ferromagnets?

Introduce an external magnetic field.

4. Mar 18, 2004

### endersdouble

Any external field? I had some idea that a constant field would only torque the magnet, not put a translational on it...but not sure how to mathematically determine forces from field B on a ferromagnet M.

5. Mar 20, 2004

### Creator

Re: ferromagnets?

Uhh; push it with your finger!

Oh, you mean produce translational motion using an external field?

You are correct; generally a uniform magnetic field only produces a torque. However, most external fields are not uniform over much of a distance; so when the poles of the magnet rotate usually one pole is 'closer' to the stronger external pole and the entire magnet translates in that direction.

However, in a large B field like the earth, small magnets have no translational motion.

There is a species of aquatic bacteria that has been found to have a built-in string of 'permanent' ferromagnets inside it (about 1 micron in diameter) pointing with the North pole facing toward its 'head'.
The earth's field doesn't 'pull' it either way, but simply rotates it to align with the Earth's North field. The bacteria has flaggella in its 'rear' that propells it forward as it points toward the earth's North pole, which by the way, is on an angle into the earth. So the bacteria always burrows into the slim beneath the waters, keeping it away from the upper oxygen rich water that is toxic to them. Quite an interesting internal guidance system.

Creator

Last edited: Mar 20, 2004
6. Mar 21, 2004