Energy in a permanent magnet question

So a nail takes away energy from a permanent magnet but an electromagnet pulling a permanent magnet does not?

A spring isn't a magnet. A spring stores energy by deformation.

A permanent magnet does not change in any way whether something is stuck to it or not. Hence it cannot absorb or provide energy. This is exactly what the over-unity tin-foil-hat people don't seem to understand.

Magnetism is caused by alignment of molecules within crystal structure. Ofcourse it takes energy (effort) to align the molecules but the molecules don't need energy to have a certain alignment. Its like sorting eggs by size. It doesn't change the egg it just makes sure they can get more money for bigger eggs.

act

well clearly it does as observed by the paper that I attached and somebody else tracked down.

I didn't say it generated its own energy or was a perpetual motion machine. I was asking about where the original energy went when you pulled off the nails and we see it must go back into the field. In this respect it is a bit like a capcitor. A magnet must lose energy eventually though as energy must be also released as sound ,heat etc

Hardy

Good point. If the nail slams into the magnet, its kinetic energy is lost.

If you don't believe in conservation of energy, you need a new hat.

I've read the paper and I still can't get rid of the feeling its a bogus number to easely compare different permanent magnetic materials.

If this energy would be for real, then a magnet would explode when heated beyond the curie point because of a chain reaction releasing the energy. Same goes for the situation in which the magnet is cooled down. Would it freeze up when it sucks in all the energy to get its magnetism back?

No, its absorbed by whatever is holding the magnet. Same happens when you drop the nail on the floor.

It would certainly convert the stored energy to additional heat, but it would be a small amount, not enough to cause an explosion. A small supermagnet probably doesn't store many joules.

Well, it's lost to us, unrecoverable. It converts into heat and sound and maybe a tiny bit of electromagnetic radiation. But it's gone from the scene.

If, while the nail was being pulled in by the magnet, we let it turn a tiny windlass, and spin a tiny generator, we could recover that energy, and let the nail make a gentle landing on the surface of the magnet.

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There is a thing called magnetic cooling which I have never understood.

The thing is that conservation of energy has nothing to do with it because there is no energy in a magnet to begin with. Again: the magnetic field of a permanent magnet is caused by molecular anlignment. Its the state of the material not an energy level.

Think of a magnet as a brick made of clay. A clay brick needs to be baked but that doesn't mean the energy needed to bake it is encapsulated in it.

And how much energy is required to pull the nail back and repeat that? You're walking the slippery perpetuum mobile slope here.

You could start your experiment by sticking the nail to the magnet and then wind the windlass and see how much energy it takes to pull the nail away. Does the magnet 'eat' that energy?

A magnet is usefull as a catalyst when converting motion into electricity and vice versa. However such a conversion will only work when either electricity or motion is added.

Arguably, the same entropic state applies: there are more permutations of eggs (or atomic spins) when in an apparently randomized state than there are when lined up in order. The thermodynamic energy associated with this state is miniscule per object, so we don't notice eggs heating up when we sort them; there's a whole mess of spins in a magnetic material, though, and magnets do, in fact, get quite hot during manufacture (in electrical terms, they have huge hysteresis losses!).

Tim

Sure it is. And vice versa. A spring "pushes" because electrons are pushing against electrons; same reason a magnet doesn't like to be magnetized. Electrons shmelectrons, everything is electrons :^)

Tim

What you'll see in the T vs. t curve (that's temp vs. time...) is a big jump upwards at curie. That is to say, suppose you place the sample inside a perfectly insulated chamber and apply constant power to it. If heat capacity (Cp) is constant, temperature will rise linearly with time, forever. But since the curie point releases the stored magnetic energy, temperature will jump up suddenly, as if the material instantaneously had infinite Cp. The delta T divided by Cp is how much magnetic energy was stored.

Tim

Statistical mechanics says they are one in the same. All states have an energy level associated with them, even abstract information -- the sheer nature of states and their statistics, with no physical energy intrinsically associated with them.

Actually, sintering releases energy, because it makes crystals grow and densifies the product. The release, of course, is very small, too little to save any fuel in the kiln.

Tim

Not at all. When the magnet pulls the nail into itself, work is done. That's simple mechanics. The energy can be wasted, as heat and sound, or it can be recovered with the tiny windlass thing. When you pull the nail away from the magnet, you have to do work. This is no more complex than putting a jar of pickles up on a shelf, and taking them down.

The magnet is in a different state when there's a nail stuck to it, as opposed to when there's no nail. Obviously the presence of the nail reduces the overall reluctance of the magnetic circuit. So the stored energy in the system is different.

Catalyst? What does that mean?

Right. A similar principle is used to generate millikelvin temperatures, namely a change of temperature caused by a change in magnetization state.