Hang on a tick, I have no great knowledge when it comes to this science stuiff, but it’s covered with a layer of water ice, right? Which was in the air and froze when it came into contact with the disk, yes? And the mist is water evaporating from the ice, right?
Doesn’t that mean that the surface of the ice is at zero degrees centigrade, which can be safely touched? Or should that be the triple point?
Kinda sorta. Why is it the superconducter has to be so cold?
The short answer is that it won’t superconduct unless it is. For pretty much every material, there’s some temperature below which it’s a superconductor. For most things, that critical temperature is only a few degrees above absolute zero (which is horribly impractical). For some cleverly-designed materials, though, like the one in that video, it’s warm enough that they only need to be down at liquid nitrogen temperatures.
Now, if you’re asking for why there is a critical temperature at all, I’m sure that there are folks here who could explain it, but I’m not sure there’s any simple explanation (i.e., one not requiring quantum mechanics).
I don’t think there is any theoretical prohibition of room temperature superconductivity. But then there is no theoretical prohibition of cold fusion either.
When superconductivity was first discovered about 100 years ago it only occurred in materials close to absolute zero. The theory is that at such very low temperatures electrons pair up, which prevents them from interacting with the other charges in the material. They flow freely, without any resistance.
“High-temperature superconductors” still need to be chilled to below room temperature to work. But they operate at temperatures far higher than absolute zero. *Why *they work is an open question in physics. According to the theoretical model for traditional superconductors they shouldn’t. Whoever figures out the mechanism for high-temperature superconductivity will probably win a Nobel prize. And it will tell us if room temperature superconductors are possible.
Highest temperature superconductor to date has the transition temp. of 133K (-140C).
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Here’s the way I remember it. The way the exterior magnetic field can’t “penetrate” it can be interpreted another way. Because it is a superconductor current flows easily and freely without resistance. The exterior magnetic field creates an electric current in the object which then creates a magnetic field of EXACTLY the same strength and opposite orientation of the exterior field. When you add the two up inside the object, the sum is zero.
The closer the object gets to the magnet the stronger the interior field and the exterior field, which are by definition opposite and repulsive. When the distance is such that the repulsion strength of the two fields equals the weight of the object thats the height at which it will hover.
Also note that this object will hover in a stable position over a magnet. Its is because of this very precise and opposite field. You try to do the same with two regular magnets and one will flip or slide off the side without some sort of mechanical restraint. I’ve made these supperconducting nuggets before. Its pretty easy and damn cool.
Oh, and other high falutin shit I don’t understand.
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Well, maybe that title’s more descriptive, but a more evocative version would be “Kin sumbody dumb dis outer-space moon-man magic floating dealy fer me?”
Good point 
LOL
The explanations above are correct, but leave an important part out. How can he “lock” it in various positions and still have it levitate?
First, to review: The puck is a high temperature superconductor, possibly Yittrium Barium Copper Oxide (YBCO), which has a transition temperature of ~90K, safely above the boiling point of liquid nitrogen at 77K. A property of a perfect conductor is that it acts like a magnetic mirror. If you put a magnet near a superconducting plane, currents will flow that create a magnetic field that is the mirror image of the field of the magnet. As explained above, if the superconducting puck is lowered onto the north pole of a magnet, the reflection will also be a north pole and the magnet and the superconductor will be repelled from each other. If the magnet is strong enough, the repelling force will be great enough to levitate the puck before the two objects touch. If a perturbation pushes the puck up, it will fall back, if it pushes the puck down, it will be pushed back up. Thus, in the vertical direction, the levitation will be stable.
This does NOT explain a few things: 1) What makes it stable in the horizontal direction, i.e. why doesn’t it slide off the track, or how does it go around the circular track without shooting off at a tangent? 2) Why is it stable when tilted at an angle? and 3) Why in heavens does it work upside down, when gravity and the repulsion are pushing in the same direction?
The answer is “trapped flux”. This is harder to understand, but basically, the story so far is oversimplified. It is possible to overwhelm the superconductivity and cause the magnetic field to penetrate the superconductor, instead of being perfectly shielded by the mirror effect. When that happens, the puck becomes a permanent magnet imbedded in a perfect (or almost perfect) conductor. The magnets in the video are very powerful rare earth magnets, which exceed the critical fields in the puck and cause magnetic flux to be trapped in the superconductor. When he tilts the puck at an angle, a field is trapped and “locked” in place, but the position is stabilized by the magnetic mirror effect. It would take some pictures and some hand waving to explain this thoroughly.
I like how I asked you to dumb this down for me and each explanation becomes more and more baffling. heh
Welcome to the world of physics…
Sorry, but it is hard to dumb down this complex interaction. In simpler terms:
The superconductor acts like a “locked in” magnet surrounded by magnet that changes when the superconductor moves. The changes occurs in such a way as to counteract motion in the directions in which motion is constrained. The strength and position of the “locked in” magnet changes when the superconductor is moved in the presence of strong magnets.
Seriously. I believe there are “math people” and “word people” and I’m am obviously not “math people.” Likewise, my husband the physicist is not “word people.” He is obviously very very smart but we played Scrabble once (ONCE) and it was torture. He would stare at the tiles for like half an hour then play “C-A-T.”
Physics in high school was hands-down my worst subject.
When you two are getting frisky some night just tell him to “integrate you piecewise”…you’ll both be happy, trust me.
Is this different from conventional levitating superconductor demonstrations? Because I heard about this in some news, so I thought there might be something different about it. Also, I’ve never seen a magnet/superconductor hold its position in space, only float.
It doesn’t move even when turned upside down, meaning the magnetic force can change as gravity changes. Does it just oppose motion?
“BOOOOOO! Down with motion!”
#occupyphysics
I mean, in other superconducting levitation experiments like Magnetic Levitation - YouTube the magnets hover where THEY want to, but here he can just position it however he wants. Maybe it has something to do with his magnets, looks like he’s using a few. Maybe a complicated magnetic field gives the superconductor more “grip” or something.
To explain more about opposing motion, why can it be moved by hand, but doesn’t succumb to gravity? What would it feel like moving the magnet - like moving it in a viscous fluid?