# Basic magnet question

1. Jul 25, 2008

### Green Zach

Ok so, i think this is kinda a basic question but here goes. I am building a machine that uses magnets and desperately need to eliminate a zero point so the movement will be smooth so what i need to know is if you have a magnet being attracted to substance Q and the magnet has a 3cm distance from substance Q and is being attracted to substance Q at a force of X then will an identical magnet repelling substance Q at a distance of 3cm experience a force of -X? or is their a distance ratio? Of course substance Q is magnetic with + and - poles. any info or help would be greatly appreciated.

2. Jul 25, 2008

### WarPhalange

Could you draw a picture? That description is really confusing.

Is this it? M -- Q -- m Where M is the first "attractive" magnet and m is the 2nd, "repelling" one.

My initial guess would be that you are right.

3. Jul 25, 2008

### Gokul43201

Staff Emeritus
The force comes from the field gradient due to Q at the position of the magnet as well as the pole strength, length and orientation of the magnet. If the field due to Q is isotropic, then the gradient will be the same at all positions 3cm away from Q. The important thing then is to get the second magnet to have the exact same dimensions and the exact opposite orientation to the first. I assume that Q is fixed rigidly and thus, can not move.

4. Jul 25, 2008

### Green Zach

so as long as both magnets A and B are identical than both + and - forces should be identical?

5. Jul 26, 2008

### Gokul43201

Staff Emeritus
Yes, so long as A and B are placed in virtually identical positions.