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My weight increases, but does the scale say zero?

  1. Mar 13, 2010 #1
    This is a general question, not requiring an equation.

    If I travel near the speed of light, I know my mass will increase. I am assuming my weight will increase, but since there is little gravitational pull, since I am not near any large objects, then my scale would say near-zero, if I stepped on a scale?

    Thank you.
     
  2. jcsd
  3. Mar 14, 2010 #2

    ehild

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    If there is no gravitation, and you are not in a spinning space craft, you can not step on the scale, but only keep it next to your feet, so as not let it fly away. You can not use scales in free space to measure mass.

    You do not feel that your mass is more than normal when you travel with uniform velocity, as your velocity is zero in your own frame of reference.
    Neither would any other scales, travelling with you, measure increase of your mass. Your mass is big for an observer who sees you travelling with speed near c.

    ehild
     
  4. Mar 14, 2010 #3
    Thank you. That helps. Hypothetically speaking, if I stepped on a scale, then the scale would read zero, because there is no gravitational pull while traveling in a ship near the speed of light?
     
  5. Mar 14, 2010 #4

    ehild

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    Gravitational pull and travelling near the speed of light are different things. If you travel in free space or just orbit around a planet or you are in a vehicle in state of free fall, you are "weightless" as both the scale and you move with the same velocity and acceleration. No need to travel near the speed of light.

    Special relativity makes distinction of the mass measured from different frames of reference. If the observer measures the mass of an object that travels with some speed relative to him, he would measure the mass bigger than the "rest" mass. An observer travelling together with the object would measure the rest mass. If you travel alone in free space, far away from anything you even do not know your speed.

    ehild
     
  6. Mar 14, 2010 #5

    ideasrule

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    Have you seen videos of astronauts in Earth orbit? Imagine one of them trying to step on a scale.
     
  7. Mar 14, 2010 #6
    That is what I cannot reconcile with. The astronauts in the space shuttle, when orbiting earth, would not be able to step on a scale.

    That makes perfect sense.

    Thank you again for your time.
     
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