Or, why is there no energy expenditure required for a magnet to continue emanating its magnetic field? With an electromagnet, the magnetic field turns off with the electricity. But that doesn’t happen with an ordinary magnet. Why?
My search-fu has failed me. All I’m getting are sites which say that magnets don’t wear out in any meaningful timespan and sites that talk about the differences between magnetism and gravity.
Why should there be an energy expenditure to continue emanating a magnetic field? Does the chair you’re sitting in need an energy source to continue to support you?
Does the field lose strength if it is used to move something?
Non-magnetic materials also emanate magnetic fields. They’re just small and not lined up so as to create a macro effect.
Magnets can lose their strength over time but it is a slow process and not due to expenditure of energy but rather as the alignment of the atoms that allow the magnetic field slowly change.
Heat and other magnetic fields can damage magnets and demagnetize them in short order in some cases.
Moving electric charge is what causes magnetism. In an electromagnet, mains electric current causes the charge to move (that’s what “current” is, moving charge).
In a permanent magnet, the electrons orbiting the nucleus of the atom are the moving charges. And atoms don’t ever stop moving. The reason everything isn’t magnetized (because it’s all made of atoms with moving electrons), is that usually each atom is its “own magnet” and they all point different directions and cancel out overall. In a permanent magnet, that isn’t true. All the atoms line up and amplify the magnetism instead.
Chronos at his most Yodetic.
Because it exerts a force on other things, which should require energy. Put a magnet near an iron ball bearing and it will attract the ball bearing. Slide a magnet down a silver ingot and it will slide slowly.
I’m not a physicist, okay?
There you are pitting gravity against the tensile strength - the bonds between the atoms - of the material.
Thank you. Excellent concise explanation.
OK. Take a magnet, take a ball bearing, and put the ball bearing in a tiny little chair attached to the magnet. Does that make the analogy clearer? 
Nope, that’s why I mentioned the chair. Your chair is also exerting a force on something else, namely, you. If you’re not surprised that your chair doesn’t need a power source, why, then, should you be surprised that a magnet doesn’t, either?
Especially, of course, since they both work in fundamentally the same way: The forces your chair uses to support you are also electromagnetic forces.
The misconception that force requires an energy source is why people keep trying to build perpetual motion machines by arranging magnets in complicated ways. The earth exerts a force on you, and on me, and on everything else in the universe. It’s been doing this for billions of years. Is there an energy source powering this gravitational force?
The force behind magnetism is always there. But in most materials each individual magnetic particle is pointing in different directions, so the individual forces cancel each other out. In a magnet, the individual particles are organized so their forces are all working in the same direction and their collective effect becomes noticeable.
Ah, excellent, thank you.
Actually, the most accurate answer to this, is that it is not known. We do not know what gravity is, we only know how to measure it.
We don’t know everything about the gravitational force, but that’s just because we don’t know everything about anything. But we understand gravity a heck of a lot better than we understand most things, and we certainly know enough to know that asking “what’s the energy source” is the wrong question.
I started to write an explanation, but quickly realized that I’m just as confused as the OP. I know enough to know already that exerting a force doesn’t require energy because it isn’t doing work. But what IS work? If I repel a magnet with another magnet and use it to push the first magnet around, that’s doing work and takes energy. But if I attract the first magnet, isn’t that also doing work by accelerating the resting magnet? If I drop into my chair, isn’t there work done in changing the acceleration of my butt? Apparently not, since chairs don’t require energy. But WHY not? What things require energy and what things don’t, and how can you tell the difference? I thought I knew, but I only know example cases and extrapolate from them. I don’t actually know what the difference is.
The point with magnets and work is there’s no *net *work. The magnetic field from a small magnet on your desk extends out to the edge of the universe. Absolutely everything is influenced by it.
If you take a ball bearing and move it from 100 miles away at the factory to sitting on your desk, work was done to put the ball there. If the magnet pulls the ball a foot closer, work was done. If you use your hand to move the ball a foot farther away, work was done in the opposite direction. The net work over time is zero.
If you want, think of gravity and potential versus kinetic energy. A rock sitting atop a hill has lots of gravitational potential energy and no kinetic. After it rolls to the bottom it has less gravitational potential. But if you push it back to the top all the gravitational potential energy is back “in” the rock.
Magnetism is a different phenomenon but it works similarly in this regard.
surely you can understand that while my chair is supporting my ass, it’s only doing so by counteracting the force my ass is applying to it. The chair is not physically pulling my ass through the air into my seat.
Well, actually it is. But not nearly as much as is the very big rock the chair is sitting on. 