[Yahya A.Sharif (OP)]

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 .

[alancalverd]

No,

[Eternal Student]

Hi.

   I agree with @alancalverd.   However, there are also some explanations that could be made.   There's quite a few but I'll just offer one, you ( @Yahya A.Sharif   and/or any others ) can ask about or discuss others if you're interested.

   Explanation 1:
   The magnetic potential that you're thinking about is still there.    It just can't be accessed or converted into other forms of energy without doing something first.   In particular it won't spontaneously convert into kinetic energy in the iron ball.   
    The permanent magnet was just a collection of microscopic magnetic dipole regions.   All of those regions are still there and each region is capable of inducing a magnetic polarisation on the iron ball you were talking about.  Heating the magnet hasn't destroyed those dipole regions, it's just left them all "higgledy-piggledy" or randomly orientated.
    So there is a potential for the iron ball to be attracted to every one of the those dipole regions,  you just have to do something first to "unblock the way" and make it happen spontaneously:   One thing you could do is just re-align the dipole regions (remagnetise the permanent magnet) instead of having them all "higgledy-piggledy".

    Compare the situation with the better known example of gravity.   When we throw a ball up in the air, we would usually say it has gained gravitational potential energy.   In most situations that gravitational potential energy will spontaneously re-convert to kinetic energy in the ball.   However, sometimes when you throw it in the air it doesn't come down because it got stuck on a shelf that was up on the wall of your house.  We wouldn't say that the gravitational potential energy has been destroyed.  We know the gravitational p.e. is still there, it's just that there is no spontaneous conversion of that potential energy to kinetic energy in the ball.   In the situation the ball has got in, there is no net force on the ball (the ledge is providing an upward force equal to the gravitational downward force).   However, we can still recover that gravitational p.e. we just need to unblock the way,  for example unscrew the shelf from its fixings to the wall (which can be done with care to ensure no extra energy was ever transferred to the ball - it just will be able to fall under gravity as usual once the shelf has been removed).   Spend a moment thinking about this,  most people will accept that the gravitational potential energy of the ball was never destroyed, it was always still there, we just had to do something first to create some pathway or mechanism to allow further changes to proceed.

   Now some people might mention that unlike unscrewing the shelf, we can't avoid putting some energy into the lump of permanently magnetisable material when you do re-align its dipole regions.   That's true but we'll be ready for that.  In particular the amount of energy needed to re-align the dipole regions is dependant only on the lump of material you are trying to magnetise.   It is not dependant on the amount of ferromagnetic material it can then attract.   Indeed every piece of iron in the entire universe now has some non-zero potential relative to your magnet,  a few strokes of your lump of material with an existing permanent magnet has not put all that energy into the lump of material.   The situation is much more like needing just a little heat to start a chemical reaction which will then proceed spontaneously in a much more exothermic way.   The bit of energy you put in to magnetise the lump  (or the bit of heat to start the reaction) has not created all the magnetic potential energy that is soon to be released  (similarly, the chemical potential that was soon released as heat).

Best Wishes.

[paul cotter]

Thanks for that ,ES. I saw that post last night and I made a short reply. I was quite tired at the time and when I read what I had posted it was largely incorrect so I scrubbed it and hit the sack.

[Eternal Student]

Hi.

   Thank you @paul cotter .
I was waiting to go to hospital last night and was just finding something to do.   (I was fine, it was someone else.  It's not really my place to talk about someone else but they're mostly OK).

Best Wishes.