Can a magnetic field be generated by a rotating object made of an electrically conducting material?
I am thinking of massive spheres, spherical shells, cylindrical shells or rings rotating around their axis of symmetry. I am thinking of materials like silver rather than iron.
The reason behind this idea is this: a conducting material is a rigid matrix of positive charges (atom rumps) superimposed on a fluid of negative charges (electrons). If the rigid matrix is forced to rotate, the fluid might not (fully or immediately) share this rotation, which would cause a net positive charge to move in a circle. Or, alternatively, if the fluid would share the rotation, it might become rarefied in the center and concentrated on the outskirts by "centrifugal" forces. In other words, it would need a "centripetal" force which could only be supplied by the electric field generated by rarefaction of the fluid in the center and concentration on the outskirts. And this would cause a net negative charge to move in a circle.