----- Original Message ----- From: "Stephen A. Lawrence" <[EMAIL PROTECTED]>
>>> My point is simply that if you use an electromagnet to lift the clip, >>> the Lorentz explanation holds and you clearly have a relativistic >>> effect. >>> >> >> Wait a minute, what do you mean by a relativistic effect? Is any particle >> moving at a sizeable fraction of the speed of light? >> > Magnetism is one of the few effects which seems clearly to be a > "relativistic effect" You are quite right indeed: http://en.wikipedia.org/wiki/Magnetic_field Although this page doesn't seem to make a distinction between macroscopic current loops as in electromagnets and the microscopic ones (electron orbits) at play in permanent magnets, I quite understand Terry's point about the mystery of the electron not loosing energy while orbiting it's nucleus leaving room to hope of tapping free energy from the process! > but which occurs when velocities are far, far less > than C. Amazingly so! In the case of a current loop, in a copper wire of cross-section 0.5 mm², carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second. ( http://en.wikipedia.org/wiki/Electric_current#The_drift_speed_of_electric_charges ) Almost unbelievable that such a low velocity leads to such a large relativistic effect, but I guess we can trust Einstein's maths :) > The predicted magnetic field of a current can be obtained simply by > Lorentz transforming the electric field from the rest frame of the > charges making up the current to the frame of the observer moving > relative to them. Remarkably, the result is a first-order effect -- > first order in the relative velocities -- unlike just about everything > else predicted by relativity. Indeed, thanks Terry and Stephen for making me less ignorant, I did remember that all electromagnetism stemmed from the coulombic force but I had completely missed the relativistic aspect of magnetic forces, which makes them frame-dependent indeed as Stephen said. Michel
