Is the energy destroyed in this experiment?

[new_scientist]

Suppose you stand on a spherical permanent magnet in space and you hold an iron ball in your hand, you can neglect the gravity force by this magnet mass. You stand and throw the iron ball upwards with some kinetic energy, the ball will eventually stops at some height because it is attracted by the magnet you stand on , now at that exact moment we heated the magnet and the magnet lost its force, so at that exact moment when the ball stops " v=0" no force is acting on the ball the permanent magnet was demagnetized. The iron ball will remain at stationary as Newton first law states, the iron ball has no any kind of energy, neither kinetic energy"since v=0 at the highest point" nor potential energy" magnetic force dropped to zero" however you actually exerted kinetic energy to throw the ball to reach that height " what is supposed to happen is the ball should return back to the magnet with the same kinetic energy you exerted or at least it should have the capability to do the work at any time so your kinetic energy was stored not consumed and destroyed .

 

[Nugatory]

There’s lots of energy in this system, both before and after, that you haven’t allowed for. There is energy stored in the magnetic field itself, there’s the energy added to the system when we heated the magnet, the collapse of the magnetic field will have produced electromagnetic radiation carrying energy out of the system, ….

You will have to do a full accounting of all these to see energy conservation. Imagine that the magnet and the object are inside an imaginary box. The total amount of energy inside the box when you’re done will be equal to the amount of energy in the box at the start, plus the amount of energy that has been added to that box from outside, minus the amount of energy that has left the box.

 

[russ_watters]

what is supposed to happen is the ball should return back to the magnet with the same kinetic energy you exerted or at least it should have the capability to do the work at any time so your kinetic energy was stored not consumed and destroyed .

Welcome to PF!

Energy doesn't get destroyed, it just gets lost sometimes, and then you have to look around and find it again. In this case you applied energy (heat) to the magnet to destroy it. The amount of heat required will depend on the current configuration of the system. The difference is your "lost" potential energy.

Please don't make this a "debunk my perpetual motion machine idea" thread, because we don't allow that here.

 

[new_scientist]

Welcome to PF!

Energy doesn't get destroyed, it just gets lost sometimes, and then you have to look around and find it again. In this case you applied energy (heat) to the magnet to destroy it. The amount of heat required will depend on the current configuration of the system. The difference is your "lost" potential energy.

Hello!
Thanks
Let's say the ball reaches 10^40 meters from the magnet, the kinetic energy I should apply to put it at that distance is relatively huge, now if I heat the magnet then the heat energy must be huge as well so that we cancel this huge potential energy. However at the same time there are millions of ferromagnetic masses in the universe at infinite distances, now what the amount of heat energy we need to cancel these infinite ferromagnetic mass potential energies? It does not matter whether I put that ball at the 10^40 m distance from the magnet or there is already another ferromagnetic piece in that distance, in either ways I need huge heat energy to cancel their huge potential energies. But every magnet on earth is demagnetized by small amount of heat.

 

[new_scientist]

There’s lots of energy in this system, both before and after, that you haven’t allowed for. There is energy stored in the magnetic field itself, there’s the energy added to the system when we heated the magnet, the collapse of the magnetic field will have produced electromagnetic radiation carrying energy out of the system, ….

The only added energies to this system are the kinetic energy the ball gains and the heat energy Which demagnetized the magnet if the ball is thrown to very far distance with very huge kinetic energy it will gain very huge potential energy, how it is possible that the heat energy added to the system to cancel this huge potential energy is just a small amount? and how this small amount of heat energy cancels all these potential energies of all these ferromagnetic objects in space at infinite distances?

 

[hutchphd]

The presence of some auxilliary magnet is irrelevant. Just because you have done work on something does not mean it has gained "potential energy" The energy goes where it wants to go, most likely into eddy currents.
This is a straw man. If you keep track of all the energy it will be conserved. (So your argument is not even wrong. )

 

[PeroK]

The only added energies to this system are the kinetic energy the ball gains and the heat energy Which demagnetized the magnet if the ball is thrown to very far distance with very huge kinetic energy it will gain very huge potential energy, how it is possible that the heat energy added to the system to cancel this huge potential energy is just a small amount? and how this small amount of heat energy cancels all these potential energies of all these ferromagnetic objects in space at infinite distances?

Assuming the magnet is small, the iron ball has very little PE. The magnet will move to the ball much more than the ball will move to the magnet. Almost all the PE of the system is in the magnet.

As you increase the size of magnet, you increase the PE of the system.

The larger the magnet, the greater the heat energy needed to demagnetise it. Thereby, the link between the amount of heat applied to the system and the amount of PE lost is understood.

 

[new_scientist]

The larger the magnet, the greater the heat energy needed to demagnetise it. Thereby, the link between the amount of heat applied to the system and the amount of PE lost is understood.

A larger magnet needs more energy because it contains more electrons that spins in different directions. But potential energy is not only about the magnet strength or size it is also proportional to the distance from the magnet.

 

[Baluncore]

You push yourself and the magnet away from the ball when you throw it. The magnet under your feet is then pushing you towards the ball. When you have the same velocity as the ball, you end the game, with some physical separation of the original system, but no differential velocity. The centre-of-mass of the arrangement, has not changed.

 

[DaveE]

Conservation of energy only applies to a closed system. You have to count everything.

 

[PeroK]

A larger magnet needs more energy because it contains more electrons that spins in different directions. But potential energy is not only about the magnet strength or size it is also proportional to the distance from the magnet.

So, let's rephrase your question. We have two scenarios. In both we have the same magnet and the same ball. In one scenario, the two are further apart.

In the first experiment, we release the magnet and ball and calculate the total energy of the system. We do this for both systems. Let's say we get $E_1$ and $E_2$.

In the second experiment, we release the magnet and ball but very quickly demagnetize the magnet by adding fixed heat energy $H$.

The total energy of the system should be $E_1 +H$ and $E_2+ H$.

But, if naively assume that the balls and magnets hardly move and the magnetic field vanishes instantly in both scenarios, then the energy of the system should be approximately $H$ in both cases. That's the first question.

And, in any case, why is the energy different in the two cases? That's the second question.

 

[russ_watters]

Let's say the ball reaches 10^40 meters from the magnet, the kinetic energy I should apply to put it at that distance is relatively huge...

No, it's really not. The force of a magnet diminishes quickly so almost all of the potential energy is in the first meter and there's almost no additional potential energy in the next 10^40-1m.

 

[Ibix]

As already noted, there is a lot of energy in the system that the OP is not keeping track of. Notably the work done in creating the magnet and the kinetic energy of the magnet. There is also an obvious energy flow in the collapsing magnetic field ($\partial \vec B/\partial t$ is not zero, so $\vec E$ cannot be, so the Poynting won't be zero either). That flow must finish passing the ball at the instant it stops moving, since it's the outer boundary of the zero magnetic field region.

OP needs to keep track of all that (plus anything else I've forgotten) in order to track exactly where the energy goes. But even without doing so the answer to the thread totle is obviously "no". Electromagnetic theory respects the law of conservation of energy in EM, which can be proven via Noether's theorem. So thought experiments about "does this violate conservation of energy" are just a game of showing who is a poor book-keeper.

Note that $10^{40}\mathrm{m}$ is about fourteen orders of magnitude larger than the current diameter of the observable universe.

 

[Nugatory]

The only added energies to this system are the kinetic energy the ball gains

That energy is not added, it was already there - it is chemical potential energy in the body of the person throwing the ball, converted into kinetic energy by the action of that person's muscles. Just another example of how we have to be really careful about accounting for all the energy....

And you have not accounted for the energy stored in the magnetic field itself, all of which is converted to some other form of energy when the field goes away. Until you've allowed for that (which will be a non-trivial calculation) there's no way of making the books balance.

As a general observation: It is not a coincidence that the magnetic field calculation is not trivial. Most conservation of energy paradoxes and perpetual motion bogosities come from setups that are complicated enough that it's easy to overlook some energy somewhere, and your problem is no exception. It is very similar to connecting the two objects with a spring, and then cutting the spring at the point of maximum separation to make the potential energy disappear - but if that were the problem you'd have no difficulty tracking where it went. The physics of time-varying magnetic fields is way more complicated, and that makes it harder to see what energy is there and where it goes.

 

[Vanadium 50]

There are some seriously long sentences here! I'm impressed!

I fear the situation is over-complicated. The energy in a magnetic field is (in appropriate units) B². When the magnet is demagnetized, that energy has to go somewhere, like the formerly magnetized iron. (The magnetized state has lower energy the unmagnetized state)

The iron ball zeroes out the magnetic field inside it. You don't have to worry about it at all because the field and this the energy is the same before and after.

 

[Dale]

Suppose you stand on a spherical permanent magnet in space and you hold an iron ball in your hand, you can neglect the gravity force by this magnet mass. You stand and throw the iron ball upwards with some kinetic energy, the ball will eventually stops at some height because it is attracted by the magnet you stand on , now at that exact moment we heated the magnet and the magnet lost its force, so at that exact moment when the ball stops " v=0" no force is acting on the ball the permanent magnet was demagnetized. The iron ball will remain at stationary as Newton first law states, the iron ball has no any kind of energy, neither kinetic energy"since v=0 at the highest point" nor potential energy" magnetic force dropped to zero" however you actually exerted kinetic energy to throw the ball to reach that height " what is supposed to happen is the ball should return back to the magnet with the same kinetic energy you exerted or at least it should have the capability to do the work at any time so your kinetic energy was stored not consumed and destroyed .

As a new scientist you should be careful about accounting for everything. You claim that energy is not conserved but without doing any calculations. For energy conservation you have to calculate initial and final energy for each type of energy in the system.

There is energy in:

The electromagnetic field
The ball’s KE
The magnet’s internal energy
The heater’s battery

Notice there is no separate potential energy in this scenario. The potential energy is part of the EM field energy.

Please feel free to quantitatively work out what each of those are in the initial condition and in the final condition. Take care in your work. Extraordinary claims require extraordinary evidence.

Note that the most complicated part will be the phase transition at the Curie temperature. This is a phase transition which generally require some care in modeling. A simpler approach would be to model a superconducting magnet that gets quenched instead. But feel free to research the phase transition instead if you prefer.

When you do then PM me and I can reopen this thread.