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Q & A: levitating weight

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Most recent answer: 04/25/2009
Q:
I understand that a floating magnet has "weight", but if for example I had two 1kg magnets and a set of scales and I placed one of these magnets on the scales with the other floating above it what would the scales read? 1kg or 2kg or something completely different (numerous practical problems of keeping the floating magnet inside the others magnets field aside)?
- Hamish Cooper (age 28)
Kolkestone, Kent, UK
A:
The weight will be 2 kg. The bottom magnet is pushing up on the top one, which in turn pushes down equally on the bottom one. (Newton's 3d law.) So the scale has to push up with enough force to support both magnets.

As you suspected, the system won't be stable. (Earnshaw's theorem.) Some sort of mechanical guide (or maybe a fancy superconducting ring) will be needed to keep the top magnet stable.

Mike W.

(published on 04/25/2009)

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