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Third law of motion

  1. Apr 7, 2013 #1

    does the Third law of motion have any thing to do with the magnetic force

    like in a electric motor ?
  2. jcsd
  3. Apr 7, 2013 #2


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    The 3rd law on the general level means momentum conservation, which always applies. In the case of magnetic interactions it is sometimes less obvoius. Do a search on 'recoil of a railgun'.
  4. Apr 7, 2013 #3

    Simon Bridge

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    Welcome to PF;
    The short answer is "yes".
    Did you have a specific example in mind?
  5. Apr 7, 2013 #4
    Well the magnetic force violates the third law, hence it was recognized that the electromagnetic field itself must also have momentum to compensate and conserve momentum in the system.
  6. Apr 7, 2013 #5

    The movement of electrons
  7. Apr 7, 2013 #6
    I am not able to find any information on what the magnetic force really is
    Is it some thing that science cant really explain at the mean time, like example what exactly causes Gravity
  8. Apr 7, 2013 #7
    No the theory of magnetism has been around for a long time, and so has the theory of gravitation.
    Magnetism is just a force exerted on moving charges by other moving charges. (Or if you're into that magnetic monopole stuff, magnetic charges as well)
  9. Apr 8, 2013 #8
    any more info ?
  10. Apr 8, 2013 #9

    Simon Bridge

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    The magnetic force is part of the electromagnetic force - which is understood, in the standard model, in terms of interactions between charged particles, such as electrons, and photons. You should look up "quantum electrodynamics".

    note: "movement of electrons" is too vague - can you be specific?
    i.e. can you think of some situation in which the motion of an electron in a magnetic field appears to violate the third law?
  11. Apr 8, 2013 #10
    Well what I mean is,

    example when we spray water at an object lets say a standing piece of plywood, the ply wood will fall down due the the force of the water particles hitting the plywood, Well how does the magnetic force work ? is there any atom,particle collisions causing the force ?
  12. Apr 8, 2013 #11
    Thre are four known forces, and the electromagnetic is one of those. When you spray water various forces come into play.

    I suggest you read a high school textbook on electromagnetism http://en.wikipedia.org/wiki/Electromagnetism

    If you do some simple experiments it becomes more obvious. eg electromagnets, deflection of a compass by current in a wire.
    Last edited by a moderator: Sep 25, 2014
  13. Apr 8, 2013 #12

    Simon Bridge

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    OK - so you don't want to talk about electrons then?

    The principle is that a photon is transferred or exchanged between charges.
    So the quickie answer to your question is "yes - there is a particle collision involved"... though, on the scale of photons, "collision" is not the right word...


    It is difficult to know how to answer your questions, or even what you are asking, properly, since you won't tell us where you are coming from. Presumably you have seen magnets work right? So what are you asking? What level are you asking from?
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