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I was wondering how strong a magnet should be in order to be able to horizontally attract 0.2 Kg of pure iron at a distance of 0.3 M. Since I know nothing about magnets, I started looking for companies that provide magnets, and what different ones they offer, and I decided to pick a bar magnet. My problem here is that I couldn't relate the formulas I found online to calculate the strength of the required magnet to the properties given on magnet providers website.

The formula I found was: (is it true in the first place?)

$F= \mu m_1m_2/4\pi r^2 $

"$m_1$ and $m_2$ are the magnitudes of magnetic poles" How do I relate $m_1$ and $m_2$ to the information that magnets providers give? The information that was on the providers website were: about Magnetic Face area, Thickness, Grade, Performance, vertical pull and slide resistance!

Lets assume normal air separation for the $\mu$.

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The force required will depend not only on the mass of the object to be attracted, but on any forces holding it back (i.e. friction). To attract a block across a frictionless surface would require an infinitesimally small amount of force... – Kyle Oman Jun 13 '13 at 18:24
@Kyle Yes, let's assume a frictionless surface. But I am trying to calculate this in numbers, is the above formula correct? I am not quite sure how to get this case into numbers :) – Omar Jun 13 '13 at 18:39
If it's a frictionless surface, then the force required approaches zero... just need the tiniest force to start the block moving (since nothing is resisting it) and that's it. – Kyle Oman Jun 13 '13 at 18:53
@Kyle, right! that makes sense! So the above formual should be for the attraction of a magnet to a piece of iron vertically against gravity. I am still wondering though, given the info from the magnet provides website, how am i able to tell what is the maximum weight this magnet can pull (vertically now) at 0.3 M, assuming the magnet is on top. Many thanks – Omar Jun 13 '13 at 19:00
What's vertical pull? What units do they give you for that? Can you link the website? – MyUserIsThis Jun 13 '13 at 20:57

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