Suppose we hold two bar magnets with opposite poles facing each other a certain distance away.
We let go and the magnets fly towards each other.
We observe that the magnets gain kinetic energy. Then work must have been done on their masses.
I am told that magnetic forces are always perpendicular to the velocity vector and hence cannot do work. But clearly here, the magnetic field has done work.
How can we reconcile the motion of the bar magnets with the statement about magnetic forces. I simply don't get it. If the magnetic field isn't whats providing the accelerative force, then what is?
Thanks :)
Answer
Yes, of course that if a field - magnetic field - is able to make a bar magnet rotate or move, it is doing work. The statement that magnetic fields don't do any work only applies to point-like pure electric charges. - Lubos Motl
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