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Newton's Third Law of Motion

  1. Oct 12, 2007 #1
    Are the forces ALWAYS exactly opposite of eachother?

    Is there a way to accelerate a mass upwards, while having the "recoil" force travel on a horizontal plan or somehow completely eliminated?

    Any and all information concerning this is much appreciated.

  2. jcsd
  3. Oct 12, 2007 #2
    Maybe events in curved spacetime would violate "equal and opposite." Otherwise, in our everyday Euclidean, inertial space, the law holds.
  4. Oct 12, 2007 #3
    That's actually not quite true. The real content of the third law is the conservation of momentum; but, there are situations where the momentum of some third thing is relevant, without exactly being able to talk about a force.

    The classic example of this is the magnetic force. If you consider two charged particles moving paths that intersect at a right angle, for example, you'll find that the magnetic forces on them are not equal and opposite. This seeming paradox is solved by the realization that electric and magnetic fields in combination can carry momentum. When one adds that momentum in, momentum is conserved without equal and opposite forces.
  5. Oct 13, 2007 #4
    ///Are the forces ALWAYS exactly opposite of eachother?\\\

    that's seems right if the forces was acts in diffrents bodies as if we have a horse hold a care ! so mybe the force acts on each body is diffrent ! isn't it :)
  6. Oct 13, 2007 #5
    My question is this: are Newton's three laws of motion as general ideas about motion correct?

    1. The first law is the principle of inertia. It states that an object in motion will conntinue to move unless acted on by an external force. And that an object at rest will remain at rest unless acted on by an external force.

    2. The second law states that the change in momentum is proportional to the external force.

    3. The third law is that for every action there is an equal and opposite reaction.
  7. Oct 13, 2007 #6
    for which case u ask?

    u ask as general if those r right or not? this is not a specified question ! sir ,
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