Forces between two current elements and Newton's third law

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Discussion Overview

The discussion revolves around the forces between two current-carrying wires and their relation to Newton's third law. Participants explore the implications of electromagnetic theory on the interaction of these wires, particularly when they are not parallel, and question whether this behavior is consistent with established physical laws.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the forces between two non-parallel wires carrying current appear inconsistent with Newton's third law, as the forces are not parallel.
  • Another participant questions the existence of an electrical machine that demonstrates this behavior and asks for examples that violate Newton's third law.
  • It is noted that the forces in a circuit must cancel out, otherwise the entire circuit would move, which has not been observed.
  • Concerns are raised about the calculation of forces only considering the magnetic field produced by part of the circuit, not the entire circuit.
  • A participant mentions the axial magnetic component discovered by Ampère and its omission from Maxwell's equations, suggesting it cannot be expressed as a field.
  • One participant argues that free wires carrying currents cannot remain non-parallel and will rotate to become parallel due to electromagnetic torque, introducing the need for a supplementary mechanical force in the system.
  • There is a request for clarification on the formula for the axial magnetic component, indicating a lack of understanding among participants.
  • Another participant emphasizes the law of conservation of momentum and its relevance to electromagnetic fields, suggesting that changes in these fields can affect mass or momentum.

Areas of Agreement / Disagreement

Participants express differing views on the implications of electromagnetic forces and their consistency with Newton's third law. There is no consensus on whether the forces between the wires violate this law, and the discussion remains unresolved.

Contextual Notes

Participants acknowledge limitations in their understanding of the forces involved, particularly regarding the full circuit's influence and the axial magnetic component. There are also unresolved questions about the mechanical forces required in non-parallel configurations of wires.

m.s.j
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Forces between two current elements and Newton's third law

Consider two non parallel wires each carrying a current which located at one plane surface. According to electromagnetic theory, the forces between two straight and solid wires mentioned can be estimated as follow: F= i . (L x B) Where the "F" is force vector that applied to each wire and "L" and "B" are current path vector and flux density vector respectively. Also "i" is amount of current and "x" is vector multiply symbol.Therfore the vector of forces are perpendicular to "L" or wires body. Whereas two wires are not parallel, generally that mentioned forces which applied to wires can not be parallel. As you see we have two piece of material that apply two mutual forces to each other which are not alien and this is inconsistent with Newton's third law seemingly. What is your opinion?

REGARDS

MSJ

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Creative thinking is enjoyable,Then think about your surrounding things and other thought products. http://electrical-riddles.com
 
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1 - If what you are telling is true, there must be a electrical machine that shows that behavior.

2 - Magnets produce a B field because there are currents ( spin of electrons, the last I read ) inside them.

Can you give an example of 1 or 2 that violates Newton 3rd law ?

( I think that this thread does not belong to E.Enginering )

And thank you for the link (where there is a drawing of the problem ).
 
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Besides the forces are calculated taking into account just the B field produced by a part of the circuit, not the entire circuit ! I think this is the key point.

But there is still a problem if you think about two electrons ...
 
It's the axial megnetic component that ampere discovered at the same time he did the Biot-Sivart law. Maxwell did not explicitly include it in his Maxwell Equations. It seems to me that it can not be expressed as a field. Check out one of P. Graneau's books such as, "Ampere-Neumann Electrodynamics of Metals"
 
According to electrical engineering experience, two free wires carrying currents can not stable non parallel, and applied electromagnetic torque to each wire rotate them and they will be parallel after short time.Therefor in non parallel configuration of wires we need to assume one supplementary mechanical force in system which we were not considered it.
Of course in free wires moving duty we have involved with problem yet. In that condition because of magnetic field variation, the mass of magnetic field change due to wires moving. Therefore the essential principle of survival momentum is fulfilled and we can forget that inconsistent (action and reaction forces) temporarily.

What is your opinion?


REGARDS
MSJ

----------------------------------------------------------------------------
Creative thinking is enjoyable,Then think about your surrounding things and other thought products. http://electrical-riddles.com
 
Paulanddiw:
It's the axial megnetic component that ampere discovered at the same time he did the Biot-Sivart law.
Can you give the formula that gives this axial magnetic component ?

m.s.j:
the mass of magnetic field ...
I don't understant. Why don't you answer clearly ? if you know the answer.
 
alvaros said:
Can you give the formula that gives this axial magnetic component ?


I don't understant. Why don't you answer clearly ? if you know the answer.

One of these days I'm going to clean up my office so I can find stuff like this. The book I have is: Newtonian Electrodynamics by P Graneau. When I was an undergrad they brought it up one day in class, but never did more than mention it. None of the E/M books I've used since college talk about it. The Graneau book is available from Amazon, etc. The first chapter he covers ampere's derivation and experiments.

But, I can't find my copy right now, and I don't know the formula off the top of my head.
 
alvaros said:
I don't understant. Why don't you answer clearly ? if you know the answer.


Our main discussion (in electrical engineering field) is regarded static condition of system. But about your comment, I can add as follows:

The law of conservation momentum is one of essential law in classic and modern physics that shall not contravene. Also as you know the electromagnetic field similar to other forces field is a form of energy and energy is equal to mass, therefore the changing of electromagnetic field cause mass or momentum changing.


REGARDS
MSJ

--------------------------------------------------------------------------------
Creative thinking is enjoyable,Then think about your surrounding things and other thought products. http://electrical-riddles.com
 
  • #10
Also as you know the electromagnetic field similar to other forces field is a form of energy and energy is equal to mass, therefore the changing of electromagnetic field cause mass or momentum changing.
Its a clue, but I am not a detective.
 

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