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2 questions.

  1. Mar 14, 2004 #1
    2 questions.........

    I have two questions

    Is it possible create gravity on our own(i mean controlling it)

    Can anyone explain me the newtonsthird law properly??????
  2. jcsd
  3. Mar 14, 2004 #2
    You cannot push an object without feeling the effect of doing so yourself. Laymen call it common sense. Scientists call it Newtons 3rd law.
    Last edited: Mar 14, 2004
  4. Mar 14, 2004 #3


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    No, we cannot, at present, create or control gravity.

    As for the future, "hypothesen non fengo".
  5. Mar 14, 2004 #4
    To control gravity. Would be mindblowing. The concept would help so much with labor on planet earth.
  6. Mar 15, 2004 #5
    I know about the 3rd law very well ie "every action has equal and opposite reaction which is equal in magnitude but different in direction and act on different body"
    but i dont understand the term "action"
    Did newton mean Force or energy?????

    Now comming to the second question. We know that everything(force,particle etc) has an anti. Does Gravity have one??????
  7. Mar 15, 2004 #6


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    Newton wrote before some of these concepts were clarified. The modern version of Newton's third is conservation of momentum.

    Some particles are their own antiparticles, for example the photon. I believe the graviton, which is still hypothetical, is one of those too.
  8. Mar 16, 2004 #7

    I am aware of the the law of conservation of momentum.
  9. Mar 16, 2004 #8
    Wait i dont get it.

    The law of conservation of momentum says this
    "The total momuntum on a group of bodies remains conserved provided there is no externat force acting on it."

    It is not telling about the action and reaction

    It isjust telling that both total up to same before and after.

    About gravity...

    I heard that there are researches going on to find antigravity and some are succesful.
  10. Mar 16, 2004 #9
    If there were not a reactionary force, then the momentum could not possibly be conserved. "Equal and opposite" is just perfect in order to ensure conservation of momentum.

  11. Mar 16, 2004 #10

    Chi Meson

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    The old wrod for "action" means the same as the current word for "impulse." Impulse is defined as the change in momentum. So if two objects collide (call them object A and object B) and they bounce off each other, then the change in momentum of object A will be equal in magnitude to the change in momentum of object B, though opposite in direction. THis is essentially the law of conservation of momentum.

    Since impulse is equal to the change in momentum, and impulse can be calculated as the applied force multiplied by the time through which the force is applied (impulse = Ft), you can see that since A cannot touch B for a different amount of time than B touches A, the forces on each otehr also must be the same.

    So the modern statement of Newton's 3rd Law is sometimes stated as "If one object exerts a force on a second object, then the second object exerts a force equal in magnitude but opposite in direction on the first object."

    THis is the customary "high school" definition; the better definition incorporates the conservation of momentum. Either way the use of the word "action" is arcane and inappropriate.
  12. Mar 18, 2004 #11
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