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Can you build an object that floats above another object using permanent magnets?

Towlie

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Towlie
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May 22, 2009
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A while back I was playing with a collection of small, ordinary magnets and marveling at how they attract and repel each other, and I began to wonder about something: With those magnets and some ordinary building materials, such as glue, wooden sticks, and so on, would it be possible to build two objects, such that one of the objects would float in a stable position above the other object without touching anything?

One example that I thought of but never tried is to completely cover the outside of a ball with magnets, all with their north poles facing outward, and line the inside of a bowl with more magnets, all with their north poles facing inward. If the ball was then dropped into the bowl, it seems to me that it should eventually come to rest in the center of the bowl, suspended in mid-air.

Would that work? Is there some other configuration that would work? If not, why not? If so, why do you never see anything like that?
 
Towlie said:
A while back I was playing with a collection of small, ordinary magnets and marveling at how they attract and repel each other, and I began to wonder about something: With those magnets and some ordinary building materials, such as glue, wooden sticks, and so on, would it be possible to build two objects, such that one of the objects would float in a stable position above the other object without touching anything?

One example that I thought of but never tried is to completely cover the outside of a ball with magnets, all with their north poles facing outward, and line the inside of a bowl with more magnets, all with their north poles facing inward. If the ball was then dropped into the bowl, it seems to me that it should eventually come to rest in the center of the bowl, suspended in mid-air.

Would that work? Is there some other configuration that would work? If not, why not? If so, why do you never see anything like that?
Click to expand...

1) There is no possible static solution using any combination of permanent magnets, ferromagnets, electrostatic repulsion/attraction, and gravity. This is subject to Earnshaw's Theorem.

2) It is possible to do stable levitation if part of the system is diamagnetic. This is commonly done with bismuth.

3) It is possible to build a stable system in continuous motion, like a Levitron.

4) It is possible to use active feedback to stabilize an Earnshaw-constrained system. (Sense where the levitation object is moving, adjust magnets to move it back, repeat ad infinitum.)
 
Yes, the 'levitron' is one example. I've got one.

It has to be spinning to work. I dont think that stationary ones are possible unless you get superconductivity and more complex things involved than normal permanent magnets.

http://en.wikipedia.org/wiki/Levitron

 
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Magnetic levitationWP

Superconduction is very good at levitation, in some otherwise unrepeatable ways:

 
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So what happens when you drop the ball in the bowl?
 
Towlie said:
So what happens when you drop the ball in the bowl?
Click to expand...

I think your specific configuration would fail for more prosaic reasons- you are attempting to build a ball that would in the aggregate behave like a magnetic monopole.

At a guess there would be a net attraction between the ball and the bowl.


Dave
 
CNY_Dave said:
I think your specific configuration would fail for more prosaic reasons- you are attempting to build a ball that would in the aggregate behave like a magnetic monopole.

At a guess there would be a net attraction between the ball and the bowl.


Dave
Click to expand...

:)

I think that it is an experiment that needs doing!
 
jasonpatterson said:
It would probably behave much like a single pair of magnets do. You'd be able to get it tantalizingly close to balancing, but then it would turn a bit and attact instead.
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Here. This is a screen capture from a video just recently posted to another thread here.

mirrorball.jpg


Now imagine that all of those little mirrors are the north poles of magnets. No matter how the ball turns, you're still looking at the north pole of a magnet. And the inside of the bowl is the same. How could the ball and bowl possibly attract, no matter how the ball turns?
 
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Hmmm... My analysis of this is that the ball would have a net zero magnetic field.

The field would be canceled.

A special case of the same problem as the net field inside a charged ball.

Of course it would not be precisely zero as the tiling is not uniform, but it would be close.

Very like a horseshoe magnet with a keeper-bar.
 
Hi

Sticking a mess of south-poles to a ball so all the norths are pointed out doesn't make it all-north.

What you have is a fairly complex magnetic field with norths and souths leaking out all over the place in magnetic-field-potential-y hills, valleys, bumps and dips, all of different 'sizes' and strengths because it'd be impossible to tune the thing to get a uniform field.

When you drop it into a similarly, but reversed pole-ed, bowel, it'd probably wiggle around a bit... and probably a very BRIEF bit... until it finds a place where there's a large enough north imbalance getting sufficiently close to a large enough south imbalance for it to clamp down and form a NEW complex magnetic field with the ball with the magnets stuck to the magnets inside the bowl.

Please note all the 'probably's.
 
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I think what you're talking about might require a magnetic monopole if Earnshaw's theorem were to be violated. Of course, if one existed there couldn't be an equilibrium condition. Don't quote me on that though.
 
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Towlie said:
Now imagine that all of those little mirrors are the north poles of magnets. No matter how the ball turns, you're still looking at the north pole of a magnet. And the inside of the bowl is the same. How could the ball and bowl possibly attract, no matter how the ball turns?
Click to expand...

The trick is that fields need to spread out. A rough analogy is that a charge, like one pole of a magnet, is sort of constantly producing an incompressible fluid. The south poles on the inside can't spread their field out to the inside, so all their filed spread goes outside. It cancels out the field from the north pole, and so the net effect is the sphere isn't magnetic.

I think what you're talking about might require a magnetic monopole if Earnshaw's theorem were to be violated. Of course, if one existed there couldn't be an equilibrium condition. Don't quote me on that though.
Click to expand...

Earnshaw's theorem still works even with magnetic monopoles. After all, it already works with electric monopoles and gravity monopoles, so a third type doesn't change it.
 
That's an interesting site, Prometheus, but this little line bugged me.

For those that find pain relief using magnet therapy (for arthritis, sprained joints, etc.),
our magnetic rings would be ideal for you. Very nice looking on both men & women.
Click to expand...
 
SezMe said:
That's an interesting site, Prometheus, but this little line bugged me.

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Yeah, that bugged me too. Especially after all the warnings about taking their magnets seriously, the rings seem like a pretty irresponsible gimmick, too. Then again, a site that sells radioactive isotopes and dangerous chemicals to the general public probably isn't the most likely model of responsible behaviour.
 
Putting my pedantry hat on, the claim isn't actually incorrect; the magnetic rings would be ideal for those who found pain relief using magnet therapy, if any such existed. Empty sets are still sets.

Dave
 
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