Does a Toroidal Solenoid Violate Newton's Third Law?

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Discussion Overview

The discussion revolves around the implications of a toroidal solenoid powered by a sinusoidal voltage and whether it leads to a violation of Newton's third law. Participants explore the interaction between the solenoid and a conductive ball placed at its center, particularly focusing on the behavior of electric fields and forces in this context.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant claims that the setup leads to a sourceless electric field, resulting in a force acting on the conductive ball without a corresponding force on the solenoid, suggesting a violation of Newton's third law.
  • Another participant argues that Newton's third law is fundamentally tied to the conservation of momentum, which is preserved in Maxwell's equations, implying that the initial claim is incorrect.
  • A later reply reiterates the original claim of a violation, asserting that the example demonstrates this in agreement with Maxwell's equations.
  • One participant emphasizes that the oscillating charge on the ball generates its own changing electric and magnetic fields that interact with the solenoid, potentially complicating the initial argument.
  • Another participant challenges the relevance of the details of the example, insisting that momentum conservation holds regardless of the specifics presented.
  • Concerns are raised about the momentum carried by electromagnetic waves, with one participant asserting that the total momentum is zero due to system symmetry, while another counters that this is a well-established fact supported by experimental observation.
  • One participant suggests that if a valid experiment demonstrating a violation of the third law exists, it should be published, indicating skepticism towards the claims made in the discussion.

Areas of Agreement / Disagreement

Participants express competing views on whether the scenario violates Newton's third law, with some asserting a violation and others defending the conservation of momentum as described by Maxwell's equations. The discussion remains unresolved with multiple perspectives presented.

Contextual Notes

Participants reference the conservation of momentum in electromagnetic theory and the implications of symmetry in the system, but there are unresolved assumptions regarding the behavior of the electric and magnetic fields in the proposed scenario.

htg
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Consider a toroidal solenoid powered by a sinusoidal voltage. This will lead to appearance of sourceless electric field, also sinusoidally varying with time. Now consider a conductive ball in the center of the system. Let the electric charge on the ball vary in phase with the voltage applied to the toroidal solenoid. Then there will be force acting on the ball, due to the E field, but no force acting on the solenoid - the net charge on the solenoid is zero, there are no sources of the field E produced by the solenoid. This violates Newton's third law (action and reaction).
If you have thought about it earlier, please contact me at <personal email address removed>.
 
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Newton's third law is a statement of the conservation of momentum, and momentum is provably conserved in Maxwell's equations: http://farside.ph.utexas.edu/teaching/em/lectures/node91.html

The details of the scenario are irrelevant. If you get that momentum is not conserved then you have necessarily violated Maxwell's laws.
 
Just think about the presented example - it clearly shows that Newton's third law is violated (in agreement with Maxwell's equations).
 
htg said:
Consider a toroidal solenoid powered by a sinusoidal voltage. This will lead to appearance of sourceless electric field, also sinusoidally varying with time. Now consider a conductive ball in the center of the system. Let the electric charge on the ball vary in phase with the voltage applied to the toroidal solenoid. Then there will be force acting on the ball, due to the E field, but no force acting on the solenoid - the net charge on the solenoid is zero, there are no sources of the field E produced by the solenoid. This violates Newton's third law (action and reaction).
If you have thought about it earlier, please contact me at <personal email address removed>.

The "oscillating" charge on the ball creates its OWN changing E and B field which interact with the solenoid!

Zz.
 
htg said:
Just think about the presented example - it clearly shows that Newton's third law is violated (in agreement with Maxwell's equations).
Hi htg, ZapperZ just gave you the key, but really the details of your example are completely irrelevant momentum is always conserved regardless of the details.

Did you even read the link I posted? If so, what part did you not understand? I would be glad to help you learn the principles involved and understand the derivation.
 
The link you provided makes use of the idea that an EM wave carries momentum.
Even if we assume that it is true, we can see that the total momentum carried out by the EM wave is ZERO because of the symmetry of the system.
 
htg said:
The link you provided makes use of the idea that an EM wave carries momentum.
Even if we assume that it is true, we can see that the total momentum carried out by the EM wave is ZERO because of the symmetry of the system.

This is getting sillier. EM waves carrying momentum isn't just an "idea", it is a FACT of experimental observation! The fault in your "thought experiment" has already been shown.

If you think that you have found a valid experiment that violates the 3rd law, then please publish it. Till then, this is unfounded speculation that violates the https://www.physicsforums.com/showthread.php?t=5374" that you had agreed to.

Zz.
 
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