A question about magnets

[Quinn]

Imagine, if you will, that you've got a donut. Not just a regular donut, but an unusually large one, lying on a table. Now imagine you've got another donut, smaller than the first, but not quite small enough to fit inside it. That is, the outer diameter of the small one is just a little bit bigger than the inner diameter of the big one, so if you try to lay the small one inside the big one, it won't go all the way down to the table. Or rather, it wouldn't if these were regular donuts, but did I mention they're hyper-quantum donuts from the 8th dimension? That means that unlike regular matter, they can both occupy the same space at the same time. So when you lay the small one inside the big one, it does go all the way down to the table, and where they overlap they just sort of pass through one another, resulting in a kind of Siamese Donut formation. Right where they meet, they form a groove or ridge that goes all the way around the top of the Siamese Donut formation, which will become important in a minute.

Now imagine you've got a third donut (it will be the last one, I promise). It's bigger than the small one, but smaller than the big one -- a medium-sized donut. In fact, it just happens to be sized exactly so that it if you laid it on top of the other two, it would sit nicely in the groove formed where they meet. (No, it wouldn't sink to the table because, uh... its hyperdrive is broken.) It would be fairly stable there because gravity would be pushing it down into the groove, so if someone bumped the table or something, it would stay put rather than falling off (even if it weren't covered in sticky glazing). So there you would have it: one donut sitting atop the other two, supported by them, held somewhat in place by the force of gravity and the shape of the donuts themselves.

Of course, in real life we don't have 8th-dimensional hyper-quantum donuts. But we do have magnetic fields generated by ring-shaped magnets. If my understanding of magnetism is correct (which it may very well not be), it seems to me that, provided the upper and lower magnets had like poles facing one another, they would behave the same way. And if they did, then the magnet on top would actually float above the other two, without anything else touching it (like a pencil going through the middle), and without the need for an electromagnet (like those floating globes). And that would be pretty cool.

My question, for those who know more about such things than I do: would this work, or am I full of ◊◊◊◊?

Here's the thinking that lead up to this. The problem with getting one magnet to float above another is that floating is the last thing a magnet "wants" to do. It wants to flip itself over so that the attracting poles can pull toward one another. If there's something preventing it from flipping over, the next thing it wants to do is slide sideways and down, out of the range of the other magnet, like something balanced on top of a beach ball. Only if you can keep it from doing either of those things will it float. It seems to me that the position of the two lower magnets would keep the upper one from sliding because the intersecting fields would literally form a groove for it to sink into; it couldn't slide inward because it would "bump into" the inner field, and it couldn't slide outward because it would bump into the outer field. And I don't think it would flip because in order for it to do that, some part of it would have to be forced either downward toward the opposing magnets, or upward beyond their range.

I'm posting this in hopes that someone can correct me if I'm wrong before I go spend forty bucks at Wondermagnet to find out.

Quinn

 

[ceptimus]

I have one of these.

They're cool. The magnet floats in mid air, and you can pass your hand underneath it, or slide a drinking glass around it.

It only works because of the gyro stability of the spinning top. As the top slows down, and begins to wobble, it goes, 'clunk' down onto the main magnet.

I believe there is a theory that shows that no arrangement of stationary permanent magnets can produce stable levitation.

Superconducting coils can levitate in a stable way in a magnetic field however.

 

[Ziggurat]

Unfortunately I don't think you are right. I believe the problem with this idea is that the field contours, if you will, from the combined large and small doughnuts are not going to match the contour of the surface of the large and small doughnuts. In other words, your intuition about there being a "groove" in the field potential because there's a groove in the material may not be correct, and the top doughnut may still want to slide off to the side.

Apparently it's possible to stabilize magnetic levitation using a little bit of diamagnetic material such as plastic of even your fingers, positioned above and below the material being levitated. Diamagnetic materials provide all the necessary conditions for stability, but only superconductors have a large enough diamagnetic response to support levitation on their own. But if you provide the main levitation force from a conventional ferromagnet, even ordinary diamagnets (again, like plastics or biological material) can provide the small amount of force necessary to stabilise the levitation.

 

[Quinn]

I believe the problem with this idea is that the field contours, if you will, from the combined large and small doughnuts are not going to match the contour of the surface of the large and small doughnuts.

Dagnabbit, I was afraid of that. Thanks for the heads up.

Quinn