Tuesday, March 10, 2015

newtonian mechanics - Experiment which shows that Newton's third law is not true for magnetic forces



I am just reading David Morins "Introduction to Classical Mechanics". He writes about Newtons third law the following:



It holds for forces of the “pushing” and “pulling” type, but it fails for the magnetic force, for example. In that case, momentum is carried off in the electromagnetic field (so the total momentum of the particles and the field is conserved).



Some questions about this:




  • I can imagine that somehow (but it's not clear to me) the colinearity (opposide direction of the action and reaction) fails in the case of two currents because of the Biot-Savart law. However is it also possible that the action and reaction force doesn't have equal magnitudes? So which part of the law fails for magnetic forces?





  • Does the law already fails in magnetostatics? I guess not, but how to prove it?




  • This is my main question: Is there any experiment, ideally something which can be accomplished with high school lab equipment, which shows in a convincing way that Newton's third law doesn't hold for magnetic forces in general?






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