No, it's not possible to "weaken the magnets" to extract energy,
Of course it is! But then the motor stops.
It's even a trivial demonstration: assemble a group of small PMs into a single larger magnet, then give them a shove and let them collapse, performing mechanical work as they go. The single larger magnet stored energy, and we got some of it back as the small magnets randomized themselves. Yes, this is only an analogy. The small magnets are like portions of a magnetic material, or like single domains. The collapsed pile is a large weakened magnet. The magnetic domains don't individually weaken as a ferrous magnet demagnetizes. And, as my cluster of small magnets collapses, the surrounding field disappears, and this field-collapse can induce currents in a nearby pickup coil. (Measure the integrated output watts.)
Clearly the scrambling of domains can emit electrical energy and not just heat.
But can a weakening magnet emit net useful energy? (Don't answer yet!)
it only dissapates into entropy. Magnets are a force only,
No, magnets aren't a "force." It takes energy to magnetize a PM, and that energy comes back out during demagnetization. The same is obviously true of all common ferrous-core inductors, but without such a large hysterisis-loss as with steel etc.
they only provide energy when energy is put in. It also takes energy to destroy the magnets, so no.
Yes, energy is put in when we magnetize iron (for example, transformer laminations.) The energy is recovered during demagnetization. No, it doesn't take enormous energy to demagnetize a laminated-core inductor. But yes, it takes energy to exceed the small B-H hysterisis of the transformer core, and takes far more to exceed the BH threshold for steel and other permanent magnets. In my above analogy with the collapsing small magnets, we must perform some work to start the collapse. But this is a catalyst or trigger, and as I understand it, is unrelated to the energy which was stored in the magnet-array, and unrelated to the energy recovered by external coils (or attracted objects) during demagnetization.
Specifically,
if the energy recovered by the pickup coil is less than the energy required to demagnetize a material (say iron,) then some net energy can be collected as the magnet is demagnetized. This is similar to having the field of an energy-storage inductor collapse, injecting energy into the external circuit.
Note that iron-core inductors don't have zero hysterisis loss, so they give us a real-world example of the Permanent-Magnet effect I'm discussing. When the laminated core weakens, it delivers a huge kick to the inductor wound around it.
Or, if the energy required to
demagnetize a high-hysterisis material (say steel) is larger than the energy collected by a pickup coil, then as you say, no net useful energy can ever be recovered. We can only put energy in during demagnetization, and at the end, the removed magnetization ends up as heat.
Do all permanent magnet systems always consume net energy during demagnetization? I expect the answer isn't as clear as you seem to think.
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For example, if we have two magnetized steel plates with alike-poles facing, we can let them push apart, then force them back together. If their final positions match their initial positions, no net energy is been recovered or injected. Follow? We could even build a "crackpot test-motor" to demonstrate this, with magnetic steel plates carried by stator and rotor. With good bearings it would just coast along after being spun up.
OK, next, let the two steel plates push wide apart, and while they're apart, slightly demagnetize one of them. We could demagnetize a small stripe-pattern on the steel by using a tiny, powerful magnet brought close. Or we could do it with a brief current-spike in a coil. Now force the two steel plates back together. It takes less work this time, so some energy came out of the 2-plate system.
Here's the big question: what actually happens when we sum up all the energies? Not speculation, calculation. Or experiment. Did the energy required to slightly demagnetize one of the steel plates exceed the net work which accelerated the moving plates? Can a hoax-motor be (temporarily) driven by demagnetizing its own magnets?
First, don't be confident of the answer. Second, figure out what actually happens. "Faraday-style" is to let the experiment be made, since one simple demonstration is worth any number of pages of spreadsheet. (No, I haven't build one myself. Yet.)
I certainly accept that I may be wrong, and there may be no way to demagnetize a steel plate while collecting net energy from a flywheel (or net energy from a pickup coil wound around it.) But the answer doesn't look obvious whenever mechanical forces are part of the system (rather than, say, winding a coil around a steel bar.) I notice that it's not breaking laws of physics to get useful work out of a demagnetizing permanent magnet.
Hmm. Also, if it turns out to be impossible for steel, might it be possible for some other ferromagnet having a weird nonlinear BH curve, Weigand wire etc? Do the crackpots use normal magnets, or instead some weird materials?
What if some of the "magnet motors" are still a hoax, but they honestly don't contain any hidden batteries?!! To properly debunk them, build one that "really works," and measure the weakening of the net B-field. Heh, or ignore the second part, and go start your own scam company!
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