Do Lorentz Forces Really Violate Newton's 3rd Law?

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SUMMARY

The discussion centers on the interaction between Lorentz forces and Newton's 3rd Law of Motion, specifically in the context of two permanent magnets and a current-carrying wire. It is established that while the Lorentz force exerts an upward force on the wire, the reaction force is mediated by the electromagnetic field, which compensates for momentum transfer. The conversation highlights that, in a nonrelativistic framework, the magnets experience a downward force due to action-at-a-distance, while in a relativistic context, impulses are exchanged between the wire and the field, ultimately affecting the magnets. The consensus is that the missing momentum is accounted for by the electromagnetic field.

PREREQUISITES
  • Understanding of Lorentz force and its implications in electromagnetism
  • Familiarity with Newton's 3rd Law of Motion
  • Basic knowledge of electromagnetic fields and their properties
  • Concept of relativistic effects in physics
NEXT STEPS
  • Study the implications of Lorentz force on classical mechanics
  • Explore the relationship between electromagnetic fields and momentum conservation
  • Investigate the differences between nonrelativistic and relativistic physics
  • Examine case studies demonstrating action-at-a-distance in electromagnetic interactions
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Physicists, students of classical mechanics and electromagnetism, and anyone interested in the foundational principles of force interactions in physics.

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In classical Lorentz force demonstration, let's say we have 2 permanent magnets generating a magnetic field perpendicular, out from the page and a wire carrying current to the left. Thus we would expect that the Lorentz Force will exert an upward force on the wire.

According to Newton's 3rd law, there should be a reaction to this force. So do the magnets actually being pushed down? Or is there something else to compensate for the momentum?

Thanks.
 
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There are three objects: the magnet, the wire, and the field. The field mediates the interaction. Nonrelativistically, you can just consider the action reaction at a distance, so the magnet would be pushed with an opposite force. Relativistically, if the wire expreriences an impulse from the field, then the field experiences an opposite impulse from the wire. This impulse is transferred at the speed c to the magnet. If what you meant by "classically" was "nonrelativistically," then you are talking action-at-a-distance, and Newton's third law treats the two objects, magnet and wire, as interacting directly at a distance.
 

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