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carsten
Micro Wave
Germany
105 Posts |
 Posted - 02/27/2003 : 20:31:10
Hi everybody,
ever tried to have a magnet soaring freely in the air because of magnetic repulsion? OK, there's the famous spinning-top-toy. But let's exclude rotation. Then we know it won't work, no matter how cleverly we design our set-up of magnets. Somebody told me there's even a mathematical reason for it, having to do with vector-field divergences, Maxwell's laws, and so on...
But I have seen an experiment with a small toy locomotive that was filled with liquid air and soared freely some millimeters above its rails. They said the reason why this works is superconductivity. My question: Why can a superconducting object float freely, while a normal magnet can't? Thanks...
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LURCH_001
Visible Light Wave
USA
588 Posts |
 Posted - 02/27/2003 : 20:44:57
I have seen magnetic levitation accomplished with superconducting magnets. However, in all models I have witnessed, superconductivity was not the reason that the model maintained its stability on the tracks. That was due to the shape of the magnets in the track, which created a magnetic field that was more repulsive at the edges, and tended to push toward the center.Why do they call it a FIXED income, when I'm always BROKE ?!
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alexander
Gamma Wave
Russia
3982 Posts |
Posted - 02/28/2003 : 22:08:02
Yes, it is possible to make stable levitation without rotation but it requires quite elaborate combination of two ring magnets with long non-magnetic axially attached rod (to lover center of mass of levitating ring).
Life is chemistry,chemistry is quantum mechanics,quantum mechanics is math.To learn how natural laws,natural forces and natural objects originate from math,click: http://www.emmynoether.com/
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carsten
Micro Wave
Germany
105 Posts |
 Posted - 03/04/2003 : 21:06:33
Diamagnetism seems to be the key. See here (fascinating site):http://www.scitoys.com/scitoys/scitoys/magnets/suspension.html
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LURCH_001
Visible Light Wave
USA
588 Posts |
Posted - 03/04/2003 : 21:50:02
Of course, the "toy" you saw was probably a model of a maglev train. These stay on the track in much the same way as a normal train does. The magnets that levitate the train are L-shaped, with one leg above the rail, and one beside it. In order for the train to slide to one side or the other, one of the vertical magnets must be pushed closer to the rail. Magnetic repulsion prevented from going very far.Why do they call it a FIXED income, when I'm always BROKE ?!
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carsten
Micro Wave
Germany
105 Posts |
Posted - 03/04/2003 : 22:08:41
quote:
Originally posted by LURCH_001:
...L-shaped, with one leg above the rail, and one beside it...
No, LURCH_001, there was nothing beside the rail. The locomotive was rather like a box. You could have slided in a piece of paper horizontally in between the locomotive and rail... plus it was superconducting. I could see the steam from liquid air. They poured some in while I was watching.
Still, I think superconductivity creates diamagnetism, and bismuth creates diamagnetism too, and that's the key...
A diamagnetic object will push away from any magnet. This makes levitation possible...just my thoughts 
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alexander
Gamma Wave
Russia
3982 Posts |
Posted - 03/05/2003 : 20:27:08
Eddy currents on the surface of superconductor create exact mirror image of the magnet brought close to the surface. So you basicly have interaction of magnet with its mirror image beneath the surface of superconductor. Thus repulsion between the two no matter what is the orientation of the magnet.What I don't understand is why this equilibrium is not indifferent but stable (i.e. why slight horizontal displacement of magnet slightly increases the repulsion). Life is chemistry,chemistry is quantum mechanics,quantum mechanics is math.To learn how natural laws,natural forces and natural objects originate from math,click: http://www.emmynoether.com/
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LURCH_001
Visible Light Wave
USA
588 Posts |
Posted - 03/05/2003 : 21:45:32
Try looking at figure 1 on this page:
http://www.physics.brown.edu/research/cme/levitation/pdf/prl96.pdfIn this diagram, there seems to be an area of low enrgy along the axis pf the magnetic feild. Sort-of looks like the eye of a storm. Certainly in this type of feild, an object drifting away from the central axis would be pushed back? Why do they call it a FIXED income, when I'm always BROKE ?!
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carsten
Micro Wave
Germany
105 Posts |
 Posted - 03/06/2003 : 19:33:42
Yes, that seems to be it.
You need...
a) a magnetic field that is vertical at its center, and points slightly inward as you move away from the center. A ring magnet or sufficiently wide coil will do. Or 2 rails, these will give stability in transverse direction and indifferece in parallel direction. That's the 'train' I have seen.
b) an object that pushes away from any magnet, no matter what its orientation is. A paramagnetic or superconducting object will do.BTW, the 'spinning top' uses a ring magnet and floats in the 'eye of the storm'. That's why it has to be precisely weighed.
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alexander
Gamma Wave
Russia
3982 Posts |
Posted - 03/06/2003 : 22:12:03
No, I am talking about high-temp YBaCuO superconductors we have in the lab. (Cheap black ceramic disks about 1-2" in diameter and about 1/8-1/4" thick, they become superconductive at 95K, so 77 K liquid air (N2) easily makes them repell small strong Nd magnets). A magnet floats about 5-10 mm above superconductor and is in stable equilibrium. Slight push sideway make magnet slightly elevate - a mm or so, and when you remove the force, magnet returns back and down. Kinda local potential well. It (well) should not be there, I guess. Something else is messing around besides superconductivity. And this does not seem to be an edge effect - stronger horizontal force moves magnet to new location, which is also locally stable equilibrium. Near edges of superconductor disk where eddy currents are less, the magnet levitates not as high as it does above the disk center, but still in some (shallow) local equilibrium. Moving a magnet futher (beyond the edge) makes it slipping off (no more local stable equilibrium well as when the magnet is above the disk). I remember somewhere in literature they mention that these ceramic superconductors are not perfect and magnetic field partially penetrates ito them. Could this be due to that? Life is chemistry,chemistry is quantum mechanics,quantum mechanics is math.To learn how natural laws,natural forces and natural objects originate from math,click: http://www.emmynoether.com/
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Edited by - alexander on 03/07/2003 03:57:30
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