Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Madidus_Scientia on 26/12/2008 14:11:22
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I read a few of the comments attempting to explain it but wondered if someone here can explain it more elaborately.
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The block of black materiel is in fact a so called 'high temperature' super conductor which is brought to this state when it is cooled by the liquid Nitrogen that is poured into the dish.
As the magnet falls towards it currents are induced in it that produce an opposing force that resists it fall.
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but why does it seem to stick into a position, and although a current induced in it will slow it from falling why does it completely stop it? it would be a magnetic repulsive force holding it up
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The electric current is a circulating current that does not die away because the material is superconducting it effectively opposes the field of the magnet that is levitating the superconductor.
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What we have here is a very strange state.
it seems that by introducing 'coldness' which is a state wherein molecules, atoms, and all 'matter' stop their movements we 'break' the bond of 'gravity'.
We do not transfer any 'energy' to this 'system'.
We take it away.
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The electric current is a circulating current that does not die away because the material is superconducting it effectively opposes the field of the magnet that is levitating the superconductor.
hmmm, I still can't really visualise what's happening properly, do you mean a current sort of goes round in circles within the bottom peice of metal? How would that work?
What we have here is a very strange state.
it seems that by introducing 'coldness' which is a state wherein molecules, atoms, and all 'matter' stop their movements we 'break' the bond of 'gravity'.
We do not transfer any 'energy' to this 'system'.
We take it away.
The atoms will not stop their movements, this only happens at absolute zero which isn't really ever acheivable. But even if it were, it would not break any bonds with gravity. When the metal is cooled with the liquid nitrogen it becomes a superconductor, not something that blocks gravity because its at absolute zero, which it isn't.
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The electric current is a circulating current that does not die away because the material is superconducting it effectively opposes the field of the magnet that is levitating the superconductor.
hmmm, I still can't really visualise what's happening properly, do you mean a current sort of goes round in circles within the bottom peice of metal? How would that work?
The shiny disc at the top is a magnet (and will be a particularly powerful neodymium-iron-boron magnet). The black "brick" is the superconductor device (which will be a ceramic material).
When the black part is cooled in liquid nitrogen it becomes superconducting, which means that any induced (circular) currents will tend to flow forever. Bringing the magnet up to the superconductor will induce currents which in turn generate magnetic fields which tend to repel the introduction of the magnet, hence the levitation. More accurately, the currents induced in the superconductor will tend to oppose any change in its magnetic environment, hence the reason that once the magnet was forced close towards the end of the video, it could then be used to pick up the superconductor - the superconductor "wanted" to maintain a fixed separation between the itself and the magnet.
There is also a phenomenon of "flux pinning" (which I don't claim to understand in any great detail), which probably explains why (in all similar high-temperature superconductor demonstrations) the magnet is not only levitated, but also maintained at its initial angle of tilt, and without sliding off the edge of the superconductor. The induced currents are fixed in space within the superconductor, and are not free to slide around...
At the end of the video, the black superconductor was no-longer resting in the pool of liquid nitrogen; as it warmed up it lost its superconductivity, and so the magnet gradually sank back down onto it, and behaved "normally" again.
It is a universal effect of physics that a changing magnetic field (caused by anything, including the motion of a permanent magnet) will induce an electric current in any nearby conductor (often known as Eddy currents when that conductor is a sheet or block rather than a wire) which will have polarity such as to tend to oppose the motion. Conversely, any flowing current generates a magnetic field.
You can demonstrate Eddy current damping (opposing of motion) by swinging a copper or aluminium "metre rule" through the poles of a strong magnet. Although the metal is not attracted to the magnet, its swing is abruptly slowed down as it passes between the pole pieces.
The same effect is used in old-fashioned speedometers for cars, where a magnet is spun near a copper disc, the copper disc experiences a rotational force proportional to the speed of the spinning magnet. (There should be demonstrations in any good Science Museum)
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Yep Madidus:)quite right.
Sloppy writing there, the movements doesn't stop, but it do become slower, do you agree to that?
But it is an interesting phenomena as you can get it with a 'permanent magnet' too, right.
And you do take energy away in the 'near field' as I see it, even though you use 'energy' via the 'far field' to achieve it.
entropy wise sort of :)
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The really interesting possibilities will open up if one can do this at really 'high' temperatures.
Like room temperature.
And the way that experiment is done will will tell us a lot about magnetism I think.
On the other hand (tentacle?)
To do it you seem to need to 'constrict' the movements of what we call matter.
Or am I wrong there?
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Thanks for the explanation techmind
yes yor_on I agree the temperature drops
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One of the interesting aspects of this, to me :), is that here we actually gets 'work done' by reducing the amount of energy accessible to a given system.
It's somewhat 'against the grain' is it not?
And if reducing the movements of our atoms to a theoretical 'stop' we would 'disappear' them, would we not?
Much as light disappeared inside that Bose-Einsteinian Condensate when stopping it.
But appeared again after turning 'of' the 'lasers' interference.
If we want light to represent 'particles' too then this should be correct.
Otherwise we do have a definite 'chasm' between matter and light.
Low temperature research is very fascinating:)
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Read this.
http://skullsinthestars.com/2008/07/25/freezing-images-in-an-atomic-vapor/
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There's no work done other than by the fingers of the man positioning the magnet.
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'Something' allows that piece of magnet to 'float' in the air.
At room temperature it won't.'
And you do 'take energy away' from both, when 'cooling' those two objects.
So by taking the energy away you get a result that surprises me:)
How do you see what they do then?
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Work is movement against a force, if its just floating there its not moving.
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You say that "Work is movement against a force"
Could you elaborate on that some more?
If your choice is relating to the idea that work is 'energy transfered' then it seems to mean that there is no energy transfered between those two objects?
What do you see as keeping it afloat?
If i pressed down the levitating magnet and then let it 'loose' then the force acting on it, restoring the systems 'balance', would be all mine?
Or if I by chilling the 'system' using a cold gas making this object 'raise', then the 'force' acting on it would be the gas and nothing else?
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You say that "Work is movement against a force"
Could you elaborate on that some more?
Sure. Work in physics is defined as force times distance, or W = f x d.
So no matter how much weight the magnetic field is levitating, it isn't doing any work. It isn't moving it upward any distance, it is just holding it there. Resting it on the table has the same effect.
If i pressed down the levitating magnet and then let it 'loose' then the force acting on it, restoring the systems 'balance', would be all mine?
I'm not really sure I know what you mean there, but yes the energy used to force it into place comes from you
Or if I by chilling the 'system' using a cold gas making this object 'raise', then the 'force' acting on it would be the gas and nothing else?
The magnet doesn't rise when the black brick is cooled, it is positioned above it afterwards, and it is held in place by the magnetic fields. The brick is not spending any energy raising anything, it is not doing any work. All cooling it serves to do is to make the black brick a superconductor, the effects that become possible due to this being a superconductor make the magnet hover.
Just as if I glue the magnet to the ceiling the glue is not doing any work, however it is providing a force against gravity.
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I'm sure you're correct mathematically but I still don't get it.
No offense meant Madidus.
Looking at the definitions of 'work done' here.
http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Work/WorkForceEnergy.html
It seems to me that both of those objects exact a force upon each other?
A magnetic one from the influence by the magnetic field created by the superconducting disc in accord with the levitating magnet.
If I understand you right that force then does not represent any 'work done'.
Although it hinders 'gravity' wanting to bring the magnet down?
This is a good place for me:)
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I do see the analogue between matter and a magnetic field, but I have trouble seeing them as having the same 'properties'.
Just as I see glue when applied to a object as something that will act as a 'reinforcement' to the matter it attaches to.
To me Magnetism is a 'force' either created electromagnetically or already existing in so called 'permanent magnets'.
And when it 'lifts' or 'uphold' something relative 'gravity' it is acting on the system with a force?
I will have to learn more of those definitions I think:)
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Yes it exerts a force against gravity, but that doesn't mean energy is spent. Lets take this away from magnets to simplify
If I rest a brick on a table, and the brick does not break the table and fall through it, then the table is actually exerting an upwards force on the brick. If it wasn't exerting an upwards force, then nothing would be opposing the downward force of gravity on the brick, and the brick would fall. No energy is being spent by the table, because it is not lifting the brick at all, just holding it in place. It is not doing work.
Every action has an equal and opposite reaction.
The case with the ceramic brick and magnet is no different to this, apart from the fact the opposing force is transferred by magnetic fields instead of merely resting on top of it.
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Thanks:)
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happy to help