Re: Stored Energy?
Posted by Pasti on Apr 18, 2004 at 23:17
(67.69.241.85)Re: Stored Energy? (Bill Gill)
The argument is more elaborate (but not necessarily more complicated) than you might like to think.And this is because it involves magnetic fields,and with magnetic fields,if one is not careful with the arguments,it does not take very long to confuse what magnetic field does what on whom, so to speak.
The error in Robert's reasoning is that he assumes the interaction between his ball on the incline somehow consumes the energy of the magnetic field.
The reality is that if one initially considers the magnet alone in space,together with the incline (for simplicity, let's assume the incline does not interact with the magnetic field),bringing the iron ball on the top of the inclines means that one has already injected energy into the system by doing the work necessary (this means in the magnetic field) to bring the iron ball from infinity to its position on the top of the incline.Everything that happens when one realeses the ball in the incline is a "reshuffling" of the relative energies of the ball and the magnet in each other's fields.So by no means would any number of iron balls in the magnetic field "consume" the energy of the magnetic field of the magnet, since in otrder to bring them close to the magnet,an appropriate amount of energy is injected from outside intoo the system.
As for how permanent magnets are, indeed, they are not permanent in the philosophical sense of the term.Over time, relaxation processes tend to change the the magnetic field of a permanent magnet, but in general, for most magnetic materials, such relaxation processes not only are very slow, but they are also rather small, as long as you don't heat the magnet, or force some phase transition in a non-magnetic phase.