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Relative Gravity

  1. Dec 1, 2004 #1

    DB

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    What is the force that pushes your body down on a bigger planet making you weigh more? I know it's gravity, but how does more size produce more gravity exactly? And when people say you would weigh more or less on a different planet, they mean more or less relative to the earth right?
     
  2. jcsd
  3. Dec 1, 2004 #2

    selfAdjoint

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    The current effective theory of gravity is general relativity, so the explanation is in terms of that. GR says that the curvature of spacetime geometry near a point is determined by the energy and momentum near that point. Zero curvature would be euclidean geometry and nonzero curvature is some kinds of noneuclidean geometry. "Straight lines" in a noneuclidean geometry are curves. So your heavy body is trying to move on a straight line but because the geometry is different it moves on a curved path in spacetime. A curved path in spacetime embodies an acceleration. So that's why.

    And yes, the "heavier" or "lighter" on different planets is relative to Earth.
     
  4. Dec 1, 2004 #3

    Phobos

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    Right. Your mass is essentially constant, so as you move yourself (your mass) to different gravitational fields (e.g., different planets), the weight you measure (which is mass x gravity) differs accordingly.
     
  5. Dec 1, 2004 #4

    DB

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    Thanks guys.
     
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