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In connection with the FCI there was some commentary on Newton's 3rd law.
I'll mention that I learned from Fred Reif a useful, nontraditional way of
approaching the subject. Point out the "reciprocity" of the gravitational
and electric force laws: m1m2 = m2m1 and q1q2 = q2q1. From this it is clear
that the magnitudes of the two forces must be the same. A further step is
to view the contact between the big truck and the little car at the atomic
level, where one expects the interatomic forces to obey reciprocity since
they are electric in nature. This approach gives a sense of mechanism that
is lacking from the convoluted English-language version of the 3rd law. [a]
The more fundamental view is that momentum must be conserved, so that the
changes in the momenta of the truck and car must have the same magnitude
and opposite sign. [b]
An interesting point is that magnetic forces do not
necessarily obey the reciprocity relationship.....
Momentum however is conserved: there is a
change in the momentum associated with the fields, and the total momentum
of the universe doesn't change.