Re: Recycle platters from modern hard disks
You cannot make a perpetual motion machine with permanent magnets. All that happens is the magnets move until the attractive and repulsive forces cancel one another out, and the system then sits in its stable equilibrium.
In an electric motor, either the supply is an alternating current which keeps breaking the equilibrium; or there is an arrangement with brushes energising different coils in turn via the commutator so as the armature moves, a new set of coils is brought into play such that the net forces change to make it carry on moving in the same direction it just moved -- which would bring it back into equilibrium but for that pesky commutator spoiling it.
The point is, it's the changing of one of the magnetic fields -- whether in the stator as in an AC motor, or in the armature as in a DC motor -- that is what keeps the motor going. If you try to build a motor using only permanent magnets, then there will always be at least one stable equilibrium point, and it will come to rest there. You have to do some work moving everything into its initial position, and this gets stored as potential energy in the system. This may be enough to make it run for a good while, depending on friction and any load applied (and notice, no "perpetual motion machine" is ever shown turning an actual machine of any kind, not even a tiny generator and a single, dim, high-efficiency LED ..... funny, that, innit?) but it will always come to rest eventually, at a point where the static attraction and repulsion balance one another out exactly. And there will always be at least one such position -- if you can't find it, it means you have made a mistake in your working-out. The magnets will find it, every time .....
Oh, and I have neglected to mention weakening of the magnets, which would happen in fairly short order if you ever did somehow managed to extract any usable energy out of a permanent-magnet-only motor .....
Biting the hand that feeds IT
