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Q & A: Floating magnets

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Most recent answer: 06/23/2008
Q:
Hi, I was reading a document that had the following comment: "..a circular pattern of bar magnets 342 of them, have no weight if they are attached to a common sheet of metal.." and "..in short they float in the air, all 900lbs of them.." As I don't have access to the quantity of magnets and no information as to the type of metal used, I was curious as to whether or not there is any truth to this comment. Many thanks, Amanda
- Amanda (age 31)
Sydney, Australia
A:
While it's possible to get a small magnet to float in special circumstances, for example see
  ,  I don't see anything magic in the number 342.  My guess is that it would very difficult to construct such a stable system.
By the way, even a floating magnet has 'weight'. It's just that the 'weight' due to the force of gravity is counteracted by other magnetic forces. 

LeeH

Actually, if the other piece of metal is neutral or even weakly magnetic, the magnet cannot float stably. That result is mathematically rigorous, and known as Earnshaw's theorem. The only way to get the magnet to float stably, without some active input, is to have a strong diamagnet under it. Superconductors are the only practical example for big magnets.

Mike W.

(published on 06/23/2008)

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