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Clear my concept of weightlessness

  1. Jun 29, 2013 #1
    Need to ask a question.
    Weightlessness occurs when the net force acting on a body is zero.For example,consider a person in orbit.The centripetal force provided by gravity of the Earth is balanced by the outward centrifugal force therefore the net force on the person becomes zero and he becomes weightless.

    ^^Am I right?

  2. jcsd
  3. Jun 29, 2013 #2

    Doc Al

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    Imagine yourself standing on the ground. The net force on you is zero. Are you "weightless"?

    What we call "weightlessness" occurs when the support force on a object is removed, such as when you are in free fall. Or in orbit.

    "Centrifugal force" is an inertial force that appears when analyzing things from an accelerated, non-inertial frame of reference (a rotating frame of reference). I recommend that you stick to an inertial frame. There is a net force on a person in orbit, but his apparent weight is zero since the ship exerts no support force on him.
  4. Jun 29, 2013 #3


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    "weightlessness", in orbit (or in free fall) is just a state of mind. You are attracted to the Earth just the same as if you were standing on a tall tower at the same altitude. However, you are blissfully un-aware of this because everything that's going round ( the ship) with you is accelerating at the same rate.

    This is a simplification because the different parts of the ship and you are at different distances from the centre of Earth and because they are all orbiting at the same rate, there is a detectable amount of 'microgravity' between objects around you at different distances.
  5. Jun 29, 2013 #4
    If you consider a person in orbit to be in circular motion then the resultant (NET?) force is not zero. Circular motion requires a resultant force (for an object in orbit this is normally taken to be the centripetal force, Centrifugal force is not a real force !!!!) you will get lots of responses to this...good luck in sorting them out.
  6. Jun 29, 2013 #5


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    The confusion comes the fact that an inertial frame of reference in Newtonian physics is not the same as an inertial frame in General Relativity. In GR, the statement "Weightlessness occurs when the net force acting on a body is zero" is reasonable, I think.
  7. Jun 29, 2013 #6


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