# Pull Force of a Permanent Magnet at a Certain Distance

1. May 13, 2010

### sherryjenix

1. The problem statement, all variables and given/known data
What would be the necessary magnetic field strength needed to pick up a 0.1543 lb. magnetic object 0.238 meters away? (I am trying to find a permanent magnet, not an electromagnet to accomplish this)
(the pull force of the permanent magnet I am using is 4.7 lb)

2. Relevant equations

For a circular magnet with a radius of R and Length L, the field at the centerline of the magnet a distance X from the surface can be calculated by the following formula (where Br is the Residual Induction of the material)

3. The attempt at a solution
I chose a small neodymium magnet and found the magnetic field strength at 0.238 meters away to be 5.6587 $$\mu$$T. The problem is that I do not know if that is enough to pick up the 0.1543 lb. object.

Perhaps there is an equation relating pull force of a permanent magnet to the distance of the object?

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