The forces that keep in place are equal to its weight. How hard is it for you to pick up a sugar cube? Thats about the amount of force the hand has to exert to move that nugget around. You could feel it, but its not going to be obvious or hard to overcome.
Actually, Scrabble is a math game, not a word game. But of course, math is a very large field, and someone might be good at some aspects of math without being good at others.
When you’re not holding it, yes. But I suspect it’ll need more force than that to move it, otherwise it would move when turned upside down.
The more explanatory video talks about “quantum flux tubes pinned in defects”. I took this to mean that the thin superconducting film they applied has small holes (perhaps actual holes, or just defects in the crystalline lattice). The flux tubes get trapped going through these holes, and don’t move around easily, and so the disk stays locked in place.
In those other videos, the superconductor is quite thick, and so there are no defects large enough that the flux tubes can flow straight through. You get the levitation, but not the locking effect.
Maybe someone else can confirm this; I’m no expert.
Can one of you sciency types either confirm my guess, or explain why it’s wrong?
Living room Scrabble = word game
Tournament Scrabble = math game
…A math game involving memorizing certain agreed-upon strings of base-26 “digits”, then strategically laying down these variable-length “digit”-strings on a playing board in a manner which gains you as many points as possible while limiting your opponent’s scoring by blocking his/her access to prime scoring opportunities.
Or something.
A couple of the top players in the world can’t converse in, or read or write English beyond the lists of playable Scrabble words. I think that’s an elegant illustration of Scrabble not being about language or vocabulary–at least at the elite level.
Oh, I see what you are thinking now (though my point about the relatively small force required still stands). You are thinking that magnetic field inside the superconductor is fixed relation to the superconductor. It is not. The orientation of the field in the superconductor is fixed in relation to the magnetic field that exist from the other magnet outside the superconductor. If the superconductor was a perfect sphere and perfectly uniform you could spin it any way you wanted and it wouldnt make any difference (though I suspect some really high speed spinning might bring up secondary effects). Now if superconducting nugget is not perfectly shaped and perfectly uniform there will be some minor self adjustments as you change its orientation in relation the exterior magnetic field.
It is possible (not sure one way or another on this) that if you tried to move that nugget really fast the force level required to move it would go up significantly.
As mentioned above, this is all a result of flux trapping. Indeed the flux is quantized, but I left this out, since we were asked for a dumbed down version and I don’t think the quantization is necessary to explain the effect. The essential point is that magnetic flux can penetrate the superconductor, leading to a locked-in remnant magnetization. The fluxons (quantized flux lines) are pinned by defects in the polycrystalline structure of the superconductor. It takes some force to move the flux. When the guy in the video moves the puck to a new orientation, he is working against that force, changing the position and orientation of the fluxons trapped in the puck. Another detail is that the track is made up of multiple magnets with the directions of the magnets arranged to stabilize the lateral position, while allowing the puck to move along the track.
The mist is water condensing in the air that is being cooled by the puck. The layer of ice on the puck is growing as more water vapor condenses on it. The surface temperature of the puck can be anywhere between the freezing point of ice (273 K) and the boiling point of liquid nitrogen (77 K), which is where it starts when it is first pulled out of the liquid nitrogen.
Thanks for your reply. I was just wondering how it would feel to move the magnet (guess I’m the more hands-on type). From the video it looks roughly like posing an action figure - independent of position (doesn’t get harder to push them close together, unlike pushing 2 repelling magnets), independent of speed. It would be like moving a neutrally buoyant object through a viscous fluid? But I suspect it should depend on speed, since induced voltage depends on rate of change of magnetic field.
I’m also wondering:
[ul]
[li]what’s the maximum force the magnets can exert - clearly more than the weight of the magnet, less than what the person applies by hand[/li][li]what this depends on, the strength of the magnets? critical value of magnetic field when superconductivity breaks down?[/li][/ul]
Looks like you’re right about uniform superconductors, with the ring magnet the superconductor can spin. I suspect the grid has alternating poles, which creates enough variation in the magnetic field for it to hold its position.
We made this stuff shortly after the big news came out, 1987? give take a few years. The stuff is easy to make. Somebody probably has little science kits for sale with all the ingredients and instructions these days.
Ours was just a simple nugget over one simple magnet and I don’t recall any serious effort being required to move it around. My memory of it isnt enough to say what the level of effort required was with a decent level of precision. I can say I don’t recall it being like trying to move it through a very viscous fluid. Then again its been so long that memory might even be wrong.
Yes, that’s right. In the first magnet the magnets are laid out in a checker board pattern like:
NSNS
SNSN
NSNS
SNSN
the second one where it spins is more like:
NNN
NSN
NNN
(only round!)
The track is like:
N.N
N.N
N.N
N.N
N.N
So in the first example the superconductor can’t move or spin at all without feeling different magnetic fields, and those changes in the field would create strong currents trying to push/pull it back to where it was before.
The second it can spin, but can’t move in or out or fall off.
With the track it can move along the line of the track without feeling any difference, but cant fall off (even when held upside down), again because the magnetic field would stop penetrating the puck, and as the puck left the field it would start up a big current to pull it back.
Actually on the second thoughts the track is probably more like:
N.S
N.S
N.S
N.S
N.S
(I just noticed in the other video that they’re using an iron backing plate on the track so they would be using alternate poles as this doubles the strength).
We’d play with liquid nitrogen in physics lab all the time, and a few times would smuggle out a dewer for home entertainment 
If you’re careful you can “hot potato” handle chilled objects quite easily, just have to maker sure your hands are absolutely dry so you don’t get a tongue-on-the-flagpole situation happening. Items with a rough surface can be held for quite a long time this way (less surface area contact)
Liquid N will also insulate itself with a thin gaseous barrier that can insulate for short periods. For example, you can dunk your entire hand quickly in and out of a bottle of the stuff with only a mild chill. More than that, though, and you quickly cross over into massive frostbite burns.