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  1. Oct 24, 2004 #1


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    I had an idea which i cant fully realize because i dont know the physics behind it. Here it is: imagine two particles, for example a and b. imagine also that a is attracted to b but b repels a. In this case, both atoms would essentially travel in a straight line forever assuming they repel and attract each other with the same force. what is wrong here? i know this cannot exist because it is a perpetual motion contradiction (there is no perpetual motion). But at the same time, they could go at a constant velocity, that is no acceleration. Can someone explain this to me in greater detail?
  2. jcsd
  3. Oct 24, 2004 #2


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    Why not just take two particles that are neutral and set them off into space with the same velocity? It would be the same thing.
  4. Oct 24, 2004 #3
    If it could exist, then a negative mass would act as you describe. With mass negative, then acceleration would be in the opposite direction from an applied force.
    Example: Take two particles at rest, one with a unit of postive mass and the other with a unit of negative mass. Place a positve charge on one particle and a negative charge on the other, and release. The force on each particle is directed toward the other particle. The positive mass particle accelerates toward the negative mass particle. The negative mass particle acclerates away from the positive mass particle and an accelerating chase begins.

    Note that because the net mass of the two particle system is zero, the two particles together can accelerate without an increase in momentum or kinetic energy, so the system speed would eventually approach c. Speculating wildly, this could be the basis for explaining why no one has ever seen any negative mass, because it would be rapidly ejected from regions with a preponderance of positive matter.
  5. Oct 25, 2004 #4
  6. Oct 25, 2004 #5
    but it wouldn't violate thermodynamics cause there doesn't need to be friction
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