How is magnetic energy supplied, v. 2.0?

Question

This is a follow-up question to my Physics SE question from yesterday:

How is magnetic energy supplied?

The kind responses were very informative, but I still have much to understand about magnetism, as follows:

Scenario:

Imagine a piece of iron laying on an infinitely large flat surface. A magnet is also positioned on the surface, some distance from the iron. The iron is thus attracted to the magnet and slides sideways across the surface. As the iron moves, the magnet is moved in tandem with it such that the iron is never allowed to contact the magnet. Thus, the sliding iron is forever "chasing" the magnet across the surface.

Question:

Friction from the iron sliding across the surface results in dissipated heat and sound energy. Since energy can never be created nor destroyed, I presume that the heat and sound energy is derived somehow from the magnet. What then, is the source of that energy, and how is it constantly supplied to the magnet?

Answer 1

That implies a resulting energy deficit in the magnetic field

I think all of your questions ultimately boil down to some variation of this statement.

So...

The problem is that you're ignoring everything before and after "the event". You're creating an artificial line around the system, both physically and in time, and noticing there's a change in energy inside that line and wondering what is going on.

But if you simply expand the line a little the mystery will go away. For instance, you have noted that when the iron bar moves to the magnet (in the static case, no belt), it gave off heat due to friction. So that must imply that the magnet has lost energy somewhere?

No. Simply placing the iron on the sheet required energy. It required energy to keep it away from the magnet in the first place. Think about it - if the magnet is strong enough to pull the iron bar when it's sitting on the surface, then it's strong enough to pull it when it's in your hand before putting it on the surface. So you had to expend energy to keep it away from the magnet when you put it down. That's the energy that ultimately came out as heat (and sound).

So when you see a potential paradox or missing energy, ask yourself "how did we get here in the first place?" - move the line you're drawn around the experiment and see what suddenly appears. For instance...

There is a ball at the top of a hill. It rolls down the hill and hits a box. That gives off heat. Did that energy come from gravity?

No, the energy came from you walking up to the top of the hill to put the ball there in the first place.

This is going to be true of all "conservative" forces, like gravity or magnetism (or lots of others).