0
$\begingroup$

May I know if we have a current flowing through a wire, and the wire is between two strong magnets. The wire would experience a force called the Lorentz Force given by F = IxB, or F equals I cross B. Based on Newton's third law of motion, will the magnets also feel a force in the opposite direction of the wire?

enter image description here

In this case the wire is feeling a downward force. But by Newton's third law of motion will the magnetic around it feel an upward force?

$\endgroup$
3
  • 4
    $\begingroup$ There is a good answer on this in this answer: physics.stackexchange.com/questions/114466/… Newton's 3rd law is not violated, but you must rethink what actually exerts this force on the wire. $\endgroup$
    – Steeven
    Nov 30 '16 at 17:44
  • $\begingroup$ @sammygerbil The accepted one $\endgroup$
    – Steeven
    Nov 30 '16 at 22:05
  • $\begingroup$ @Steeven: I don't think the question you've linked to is really a duplicate. One can derive Newton's Third Law directly from the Biot-Savart Law and the Lorentz Force Law, without any reference to electromagnetic field momentum. Moreover, EM field momentum is only present when you have both $\vec{E}$ and $\vec{B}$ fields (since the momentum density is proportional to $\vec{E} \times \vec{B}$.) There's no electric field here. $\endgroup$ Dec 1 '16 at 22:03
0
$\begingroup$

Force exerted by magnets onto objects can appear at first to not obey Newton's third law because the objects don't directly interact with each other and instead create fields that interact with each other. Those fields do carry some amount of momentum which is what is decreased when the field exerts forces on objects inside of itself which balances Newton's third law for electrodynamics.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.