Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] feeler-dealer, third law, et cetera



There's also the well-known case of lack of reciprocity for magnetic
forces, which makes the answer to the second question be false even without
retardation. A proton at the origin moves to the right, and an electron
somewhere along the x axis is headed in the y direction. The proton
contributes no magnetic field at the location of the electron, but the
electron does contribute a magnetic field at the location of the proton.
Hence the magnetic portion of the force on the proton is not equal and
opposite to the magnetic portion of the force on the electron (whereas the
electric portion of the force doesn't have this behavior).

Of course the momentum of the universe is conserved, so that the change in
the momentum of the two particles due to the nonzero net force applied to
the two-particle system is compensated by the change in the momentum of the
field. Since the question referred to particles, it seems that the answer
has to be false.

Bruce