Conservation of energy and magnets

AI Thread Summary
Magnetic fields do not emit light or energy when static, as a stationary magnet does not produce a change in magnetic flux, resulting in no electromagnetic radiation. When a magnet is precessing, it slows down due to potential energy considerations, but once aligned, it experiences symmetric forces that cancel out, leading to no net force or acceleration. The discussion clarifies that while a magnet can exert forces, it does not continuously shed energy in the form of photons unless there is a change in the magnetic field. The concept of energy conservation remains intact, as the magnet's state does not lead to energy loss in a static scenario. Overall, the conversation emphasizes the distinction between magnetic field behavior and electromagnetic radiation.
nhmllr
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Things with a magnetic field constantly shed light. This is why a precessing magnet will slow down until it stands straight up, giving it the lowest potential energy. But if the magnet is standing straight up, it has no way to have less potential energy, but I would think that it would continue to have a magnetic pull, which would necessitate it the keep shedding photons/energy. But then what about the conservation of energy?

Thanks
 
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If the magnet is aligned in it's magnetic field ("straight up" in your reference frame) then there is a "pull" yes, in that there are forces on it. But the forces are symmetric, they cancel out; there is no net force on (and thus no acceleration of) the magnet. A static (non-moving) magnet does not produce a change in flux, so there is no electromagnetic radiation (i.e. no light).
 
Pythagorean said:
If the magnet is aligned in it's magnetic field ("straight up" in your reference frame) then there is a "pull" yes, in that there are forces on it. But the forces are symmetric, they cancel out; there is no net force on (and thus no acceleration of) the magnet. A static (non-moving) magnet does not produce a change in flux, so there is no electromagnetic radiation (i.e. no light).

So... The magnet is emitting and absorbing photons equally? Makes sense.
 
nhmllr said:
So... The magnet is emitting and absorbing photons equally? Makes sense.

I'm not quite sure there's any argument for emitting in the first place; at least not in a classical scenario. The flux pertains to magnetic field lines, not electromagnetic radiation.
 
Pythagorean said:
I'm not quite sure there's any argument for emitting in the first place; at least not in a classical scenario. The flux pertains to magnetic field lines, not electromagnetic radiation.

But the force has to be transmitted somehow, so light would seem like a way to do that.
Although if this is getting out of the range of classical mechanics then I'm content with the given answer.
 
Oh wait, light's only emitted when there's a CHANGE in the magnetic field? OHHHHHH OH OH OH I see. That actually makes sense (such as with induction)

Okay I think I get it.
 
yes :)
 

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