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What exactly does the pull force of a magnet mean?


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#1 Shinok87

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Posted 4 May 2009 - 08:04 AM

Sorry if this is in the wrong section, I am new to the forum.

My question is about magnets. I am looking at a few, pull force is about 40 lbs. What does this mean, and how does that relate to the repulsive force?

Is there and equation to find out how much two magnets (40 lb pull force) will repel at different distances?

Thank you.Posted Image
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#2 swansont

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Posted 4 May 2009 - 04:10 PM

Pull force is going to be based on some standard material with a given thickness and permeability. I don't know if it is an industry standard, or if various manufacturers might use different standards.

According to http://www.kjmagneti...om/glossary.asp

Pull Force - The force required to pull a magnet free from a flat steel plate using force perpendicular to the surface. The limit of the holding power of a magnet. The pull force listed is actual data acquired by testing using our state-of-the-art force test stand.

(They go on to provide a table of pull forces for magnets they sell.)


Magnets are dipoles and their field drops off as 1/r^3 The torque you get from two dipoles is given here
http://en.wikipedia....agnetic_dipoles


You should be able to discern the force if you know the geometry of the magnet since T = r X F


Magnetic calculator based on material and size
http://www.magnetsal...DiscMagnets.asp
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#3 kensaize

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Posted 9 April 2010 - 08:46 AM

hi i'm a regular student fun of magnets. I just wanna ask a question.

what is the farthest distance of a magnet (that has a pull force of 193.04lbs.) attracts a 10 gram metal coin?

tnx! :-)
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#4 Amr Morsi

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Posted 9 April 2010 - 09:32 AM

Since the question is about "farthest distance", then it is considering gravity.

So, equate the force of the magnet to the weight of the coin and find "d".
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#5 John Cuthber

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Posted 10 April 2010 - 01:12 PM

There's not enough data to answer the question.
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#6 Amr Morsi

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Posted 10 April 2010 - 04:26 PM

I think, John, if we have the Magnetic Force Formula, the problem will be solved. Or, do you mean shape of the magnet, susceptibility, .......etc?
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#7 John Cuthber

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Posted 10 April 2010 - 07:12 PM

At the very least, you would need to know about the size of the magnet etc. Also, if the coin is silver then the answer is "never".
There are other issues too.
The question is not well enough defined to answer it.
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#8 Amr Morsi

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Posted 11 April 2010 - 02:53 PM

kensaize..... Do you have any additional information?

Edited by Amr Morsi, 11 April 2010 - 06:07 PM.

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#9 Amr Morsi

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Posted 19 August 2011 - 04:33 PM

Pull Force =~ \frac{HPF * Pole} {R^{3}}

Where HPF is the Head Pull Force
and Pole is peculiar to each substance (magnet or magnetic) and depends upon magnetization and permeability volume, density and shape.

This is on the axis of the magnet, and deviates much more away from the axis.
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