Where does the energy come from? (magnet)

[entropy1]

If a static magnet attracts an object A, where does the kinetic energy that A acquires come from?

 

[DrClaude]

It comes from the potential energy that was previously there. The original state, before the object started moving, had a higher potential energy, so you can try to trace where that energy came from.

 

[stockzahn]

It comes from the potential energy that was previously there. The original state, before the object started moving, had a higher potential energy, so you can try to trace where that energy came from.

Due to this thread I actually had a thought that never came up: If you have a ferromagnetic material like iron in a magnetic field and you treat it and add certain components to produce an austhenitic steel (which is not ferromagnetic). What happens to the potential energy then? Especially due to the fact that magnetic fields have an infinite range ... It seems to be analogeous to switching of the mass of the body in a gravitational field - what's my mistake?

 

[entropy1]

It comes from the potential energy that was previously there. The original state, before the object started moving, had a higher potential energy, so you can try to trace where that energy came from.

I don't understand, so let me ask a second question: the potential is brought with the magnet, right? Without magnet de potential energy wouldn't be there. So where does the magnet get its potential to produce potential energy in A from?

I can image that, if A was stuck to the magnet in the first place, the potential energy would increase by retracting it from the magnet. So then is the sticking to the magnet somehow the natural state of A?

 

[stockzahn]

I don't understand, so let me ask a second question: the potential is brought with the magnet, right? Without magnet de potential energy wouldn't be there. So where does the magnet get its potential to produce potential energy in A from?

I can image that, if A was stuck to the magnet in the first place, the potential energy would increase by retracting it from the magnet. So then is the sticking to the magnet somehow the natural state of A?

That seems to be similar with gravitation and the electric field. If you have two masses or two charges respectively, there is a potential between them - if one "vanishes" also the potential energy is gone. If they stick very close together, the potential energy is zero, if they are retracted from each other you have to spend work.

 

[A.T.]

So then is the sticking to the magnet somehow the natural state of A?

It's the minimal energy state.

 

[Vanadium 50]

If you have a ferromagnetic material like iron in a magnetic field and you treat it and add certain components to produce an austhenitic steel (which is not ferromagnetic). What happens to the potential energy then?

You are describing a phase transition, just like melting ice or boiling water. There's energy accompanying a phase transition.

 

[Vanadium 50]

So where does the magnet get its potential to produce potential energy in A from?

Same place a spring does.

 

[stockzahn]

You are describing a phase transition, just like melting ice or boiling water. There's energy accompanying a phase transition.

Wouldn't that mean that depending on the strength of the magnetic field the ferromagnetic body is influenced by, the phase transition needs more or less energy?

 

[entropy1]

Same place a spring does.

Is it correct to say that objects that are attracted by a magnet already have this potential? For instance: if we craft a magnet, from then on it gives all metal in the universe some more potential. If that is so, wouldn't crafting the magnet require enough energy to account for that acquired potential?

Does spacetime structure have to do with this also?

 

[russ_watters]

Is it correct to say that objects that are attracted by a magnet already have this potential? For instance: if we craft a magnet, from then on it gives all metal in the universe some more potential.

Yes.

I don't understand, so let me ask a second question: the potential is brought with the magnet, right? Without magnet de potential energy wouldn't be there. So where does the magnet get its potential to produce potential energy in A from?

If that is so, wouldn't crafting the magnet require enough energy to account for that acquired potential?

No, the magnet does not have potential energy, the system does (magnet + whatever it is attracted to). Also, "potential" is not "potential energy". So having "potential" does not require generation of "energy".

 

[entropy1]

So potential energy is not a conserved quantity? (After all, you can always dig that hole deeper )

 

[Vanadium 50]

Total energy is conserved. How you divvy it up is not.