Newton's Third Law and Magnetism
Most recent answer: 08/07/2013
- Adam (age 38)
Sandwich, MA
Yes, the problem is not with your understanding of magnetism but of Newton's Third Law. The usual language about "action" and "reaction" is just confusing. The law is very simple. The force between two objects is the same size on each and points opposite directions on each. In other words, the sum of the forces is zero. Take two magnets and they either repel each other (opposite direction forces) or attract each other (opposite direction forces) depending on their orientation. In either case, the Third Law is obeyed. That's all there is to it. That both those possibilities exist has nothing to do with the Third Law. It applies equally to gravity, for which the only forces are attractive.
A more general picture of Newton's Third Law is to just say that total momentum is conserved. This is important for cases where boh electrical and magnetic fields are present. In those cases, adding up the forces on the ordinary "objects" doesn't give zero, because there's a bit of changing momentum in the fields themselves.
Mike W.
(published on 08/07/2013)