Let's suppose there are 2 magnets, A and B, that are within the magnetic field of each other. Then A will exert a magnetic force on B (let's name it F1), and, due to the 3rd law of Newton, every action has an opposite reaction, B will give reaction force on A (let us call it R1). Also, since B is also a magnet, B will exert a magnetic force on A (F2), and similarly due to 3rd law of Newton, A will give reaction force on B(R2). Right?

So my question is are F1 and R2, and similarly, F2 and R1 each the same? What I mean by same is, have I written a force 2 times by F1 and R2 (F1=R2)and F2,R1? Is the magnetic force of one magnet the same as reaction force of the same magnet when the other magnet applies magnetic force on the previous magnet? What is happening here?

If both F1,R2 or/and F2,R1 the same, then this means that the magnetic field strength of one magnet can be increased by placing a stronger magnet which applies magnetic force to the weaker magnet, since then the reaction of the weaker magnet will be the same as force of strong magnet, and so it will apply a stronger magnetic force as reaction (of course, its strength would increase as long as that strong magnet acts on it), is this possible?

  • $\begingroup$ Newtons third law does not apply for electrodynamics, without taking into account the electromagnetic field momentum. $\endgroup$ Feb 10, 2022 at 14:30
  • $\begingroup$ So if Newton third law doesn't work here,how does increasing current in a conductor increase the magnetic force experienced by it when a horshoe magnet is placed near? $\endgroup$ Feb 10, 2022 at 15:47
  • $\begingroup$ The force is caused by the lorentz force on particles inside the conductor. This doesn't have to be the same as the force experienced by the horse shoe magnet due to the current in the conductor $\endgroup$ Feb 10, 2022 at 21:37
  • $\begingroup$ The forces dont have to be equal and opposite. $\endgroup$ Feb 10, 2022 at 21:38

1 Answer 1


A nontrivial result from electromagnetism is that the electromagnetic field carries energy, momentum, and angular momentum. So it’s possible to construct a system where Newton’s Third Law is violated if you consider only the forces on the magnets themselves.

In practice the momentum carried by the electromagnetic field is small, and Newton’s laws are still a useful approximation.

  • $\begingroup$ I didn't understand the answer,can u please write it in a simple language? $\endgroup$ Feb 10, 2022 at 15:49
  • $\begingroup$ The action/reaction forces between magnets are almost exactly the same. They don’t have to be exactly the same, which is interesting and important, but assuming they are equal and opposite is good enough for most practical problems. $\endgroup$
    – rob
    Feb 10, 2022 at 16:10
  • $\begingroup$ So basically u mean to say that when a magnet attracts another magnet,the reaction of the other magnet to the first magnet is the same?as I have said in the question itself? $\endgroup$ Feb 10, 2022 at 18:30

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