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Forces between two current elements and Newton's third law

  1. Sep 29, 2007 #1
    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

    --------------------------------------------------------------------------------

    Creative thinking is enjoyable,Then think about your surrounding things and other thought products. http://electrical-riddles.com
     
  2. jcsd
  3. Sep 29, 2007 #2
    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 ).
     
    Last edited: Sep 29, 2007
  4. Sep 29, 2007 #3
    The drawing of the problem is shown at General Elec.Riddle 6:
    http://electrical-riddles.com/topic.php?lang=en&cat=cat_07226015114&topic=topic_07271110238

    ( talking about the drawing ) I can realize that red-force and green-force dont cancel but forces of the full circuit must cancel ( think about a circuit whith wires like <> ).
    If the forces of the full circuit dont cancel, the entire circuit will move, which has never seen.
     
    Last edited: Sep 29, 2007
  5. Sep 29, 2007 #4
    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 ...
     
  6. Sep 30, 2007 #5
    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"
     
  7. Sep 30, 2007 #6
    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
     
  8. Sep 30, 2007 #7
    Can you give the formula that gives this axial magnetic component ?

    I dont understant. Why dont you answer clearly ? if you know the answer.
     
  9. Sep 30, 2007 #8
    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.
     
  10. Oct 1, 2007 #9

    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
     
  11. Oct 1, 2007 #10
    Its a clue, but Im not a detective.
     
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