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Weight=mg and if g is the acceleration due to gravity

  1. Jun 1, 2009 #1
    this is probably a really dumb question but I just have to ask it when I am standing
    on the ground my weight=mg and if g is the acceleration due to gravity .
    but how am I accelerating I am not moving and my velocity is not changing , and how am I applying a force on earth .
  2. jcsd
  3. Jun 1, 2009 #2


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    Science Advisor
    Homework Helper

    Re: Weight?

    Ordinarily you are not accelerating, because the floor is pushing back at you with precisely the same force. This is called the normal force. When there is no such thing as a floor (for example, you are jumping from an airplane or your elevator cables break) then the acceleration of the earth produces the only force acting on you (except for things like friction) and you will accelerate (when jumping from an airplane, that's the whole point; when inside an elevator whose cables just broke it's a less pleasant effect).
  4. Jun 1, 2009 #3
    Re: Weight?

    ok I see , when we feel a force on our body if we feel , I guess what i am asking is will we always feel a force . didn't Einstein say that when we are in free-fall we can't feel our own weight .
  5. Jun 1, 2009 #4


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    Staff: Mentor

    Re: Weight?

    You don't need Einstein for that, it worked this way since Newton.
  6. Jun 1, 2009 #5
    Re: Weight?

    the earth is trying to accelerate you towards the earth but at same time surface of earth obstructs ,by newtons third law,the surface gives tou a force (R)
    such that
    mg-R=0, so you donot move
    mg=R the weigth is measurement of R
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