At school (a long time ago that is) we were taught: 1. a stationary charge produces a static electric field. 2. a moving charge produces a magnetic field, plus an electric field that is slightly different from the original electric field of the stationary charge. 3. a periodically accelerating charge like an electron in a dipole produces electromagnetic waves. For example, electrons accelerating up and down in a dipole produce waves like these: What happens if the observer moves, and the charge is stationary? Since it is the relative velocity that matters, the moving observer will experience a magnetic field (plus an electric field, slightly different from the static electric field). Observers moving at different speeds will experience different magnetic fluxes at the same point in space! So it is not a fixed property of space, the magnetic field is a property of moving charges, different for each observer depending on the velocity of each observer. But here's another interesting fact about moving observers: A periodically accelerating observer will experience electromagnetic waves, if stationary charges exist nearby. In other words, stationary charges emit electromagnetic waves, as far as this observer is concerned!!! For example an observer is going up and down at each pixel of the following picture, instead of electrons going up and down in the dipole. Also there is no dipole, only a fixed stationary charge in the centre. Here is a video of the waves experienced by observers at each pixel. http://web.mit.edu/~sdavies/MacData...7/TuesdayFeb20/graphics/SmPointDipole_640.mpg So maybe if you go to the magnetic north pole of the earth, and put a campus on the edge of a rotating disk, then at the right rate of rotation the campus will register no magnetic force! Or maybe not. Maybe I have the maths wrong, magnetic fields do not superimpose linearly, right? Can someone provide the full maths of electromagnetic forces between moving and accelerating point charges please, the full equations for the forces that is, anyone? If the conclusion is correct, ie that superposition of magnetic fields due to different rotations of the iron in the earth's core is LINEAR, then how fast does the disk have to rotate, in order for the campus to register no magnetic field? (diagram not to scale of course, magnetic field can be assumed constant in the vicinity of the campus and disk). ------------ PS. How do I show the pictures in full size in the post?