# Repulsive force question

1. Jan 11, 2010

### tj111

Hello. I'm new to the forum and I hope this is the correct place for this question. Would it be possible to lift a 200,000 lb rectangular object that is in motion using rare earth permanent magnets at each corner?

2. Jan 11, 2010

### GRDixon

Yes. Place a magnet under each corner and lift away.

3. Jan 11, 2010

### Prologue

Rofl. Or get big enough magnets and lift from the top.

4. Jan 11, 2010

### Bob S

5. Jan 13, 2010

### tj111

Thanks Bob. I will check that out.

6. Jan 18, 2010

### tj111

Hi Bob, Thanks again for your response. I checked out the calculator. My next question, being that the calculator dealt with attractive force, is the repulsive force of a magnet equal to the attractive force of a magnet?

7. Jan 18, 2010

### Bob S

The repulsive force of two same-polarity magnet poles is due to the spacial-derivative of the total magnetic energy (magnetic energy density integrated over all space):

W = 1/2 ∫B·H dVvolume

The force along x is then

Fx = dW/dx

This is the same force that attracts a magnet to a steel plate, at least it is calculated in a similar way.

Bob S