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# Can two opposing magnets held together by string be stable?

## Can two opposing magnets held together by string be stable?

(OP)
I am wondering if I could attach two disc or ring magnets by a string in their center to cause the top one to levitate? Would it be stable or would it flip?

Here is a diagram of what I would like to do.

Thanks.

### RE: Can two opposing magnets held together by string be stable?

(OP)
The diagram is here:
http://i.imgur.com/YbWP4VO.png

I am not sure why it is now showing for you.

Is there a way to determine the minimum width of the rings and the distance for it to be stable? Or would it always be unstable?

Has anyone tried this?

### RE: Can two opposing magnets held together by string be stable?

You have probably heard of Earnshaw’s theorem which says levitation with magnets is not possible under certain conditions and assumptions. One of the assumptions is no exernal forces, which is violated by your string, so we cannot apply Earnshaw’s theorem.

A little bit of experimentation with two equal size magnets suggests to me that if there is the slightest asymmetry in centering the axis of the two magnets, the magnets experience a moment which tends to flip them.

Can the string provide a reaction moment to prevent flip?

Probably not if it is simply attached from a point in the center of the face of one magnet to a point on center of face of the other magnet. There may be other configurations such as multiple loops of string that might work.

=====================================
(2B)+(2B)' ?

### RE: Can two opposing magnets held together by string be stable?

Oh, that was probably my company's firewall doing its netnanny jig.

One could imagine something that could physically constrain the floating magnet from moving around, like using a rod, instead of a string. If the rod is just slightly undersized from the hole, then there would be little chance of floating magnet from getting out of line

TTFN
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### RE: Can two opposing magnets held together by string be stable?

(OP)
Cool, thank you so much for the helpful info. I think a rod (or nail) would work.

### RE: Can two opposing magnets held together by string be stable?

I agree with electricpete. Any asymmetry will induce a moment.
Use 2 strings of equal length.

Fe (IronX32)

### RE: Can two opposing magnets held together by string be stable?

Or three if we are not in a plane..

Fe (IronX32)

### RE: Can two opposing magnets held together by string be stable?

The configuration must be stable if the string is much shorter than the magnet diameter. Then the remaining question is at what L/D does it become unstable? 1/1?

### RE: Can two opposing magnets held together by string be stable?

chaimpeck,

I'm curious, what is this going to be for?

Fe (IronX32)

### RE: Can two opposing magnets held together by string be stable?

If one magnet id larger than the other is gets easier to do.
A small fiberglass rod would be a good bet.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

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