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Newton's 3rd Law

  1. Aug 31, 2011 #1
    Does anybody know of claims that there is a way to get around Newton's 3rd Law and Conservation of Momentum and have a link to where I might find that write up?
     
  2. jcsd
  3. Aug 31, 2011 #2

    Doc Al

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    In what context do you think you can 'get around' those laws?
     
  4. Aug 31, 2011 #3
    I mean something propelling itself in a vacuum wthout throwing off mass.
    For example a vehicle that uses a heated piece of tungsten at the focal point of a parabolic mirror that sends a focused light beam backwards would qualify, although I am looking for solutions that don't use flashlights.
     
  5. Aug 31, 2011 #4

    olivermsun

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    Would that really qualify as violating Newton's 3rd law?
     
  6. Aug 31, 2011 #5

    Drakkith

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    Well, I'm not sure, but a solar sail might fit your example. Also, even though light is "massless", whatever you used to generate the power for the light would be losing mass as it's energy stores got lower, with the light carrying away that mass as momentum.
     
  7. Aug 31, 2011 #6
    You guys are right solar sails, flash lights, and ground based lasers are not violations of Newton's 3rd. There are proposals out there that may be and I am looking for a specific one that i remember.
     
  8. Aug 31, 2011 #7

    Drakkith

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    Nothing out there will violate newtons laws. At least not working designs.
     
  9. Aug 31, 2011 #8
    Do you mean a reactionless drive? I learned from another thread that it is possible to violate Newton's third law, but not in the manner that you are suggesting. And I'm guessing that it would be against forum rules to provide a link to such a site.
     
  10. Aug 31, 2011 #9
    Turtlemeister, I don't care what you call such a propulsion method.

    Are you saying that Newton's 3rd Law is some sort of scientific religious idea and any thought that it could be violated is forbidden ?
     
  11. Aug 31, 2011 #10

    Drakkith

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    Violating it? Yes. Not violating it but designing a reactionless drive? No. As long as it follows the accepted views of science then you are fine.
     
  12. Aug 31, 2011 #11

    olivermsun

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    Well, I have no idea if it has any relation to a working design, but "every action has an equal and opposite reaction" doesn't always hold.
     
  13. Aug 31, 2011 #12

    Drakkith

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    Can you give me an example?
     
  14. Aug 31, 2011 #13

    Doc Al

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    Hint: Electrodynamics.
     
  15. Aug 31, 2011 #14

    olivermsun

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    Think moving charges and magnetic fields. (I can't claim credit for this textbook example).

    Edit: Doc Al beat me to it. :approve:
     
  16. Aug 31, 2011 #15
    No, that's not what I'm saying at all. How did you get that out of my post? Anyway, here is the link to the thread that I mentioned. https://www.physicsforums.com/showthread.php?t=521781
     
  17. Aug 31, 2011 #16

    Drakkith

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    I guess I should have said: Nothing violates the 3rd law when you use it where it applies.
     
  18. Aug 31, 2011 #17
    :smile:
    That is very true. But then, the third law applies in most scenarios, but not everywhere. Then why are they called Newton's Universal Laws of Motion? They should be the Universal Except for Scenarios Involving Electromagnetic Fields and Quantum Mechanics Laws of Motion.
     
  19. Aug 31, 2011 #18
    I went to the posting that Turtlemeister refered me to and the guy who posted it thought that the link he refered to claimed a violation of Newton's 3rd but actually it didn't.

    An example of what I'm talking about; Suppose that Object 1 is attracted to Object 2 which is repelled by Object 1. Together they would accelerate away with Object 1 chasing Object 2. As long as there is energy to chase and run. The Relativistic Effect Capacitor where each plate is switched individually to one of three state purports to simulate this effect.

    Still that is not what I am looking for.
     
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