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B Gravity of hollow sphere vs. solid sphere of same mass

  1. Apr 23, 2017 #1
    Would a hollow sphere measure the same gravitationally as a solid sphere if it was the same mass?

    Just sharing an interesting question
     
  2. jcsd
  3. Apr 23, 2017 #2

    PeterDonis

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    Which belongs in a separate thread, so I have spun it off into one.
     
  4. Apr 23, 2017 #3

    PeterDonis

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    As far as its external gravity, yes (assuming it also had the same radius). Internally, the stresses and spacetime curvature would be different, but these differences would not show up in the external field.
     
  5. Apr 23, 2017 #4
    Oh yes sorry bout that and thanks
     
  6. Apr 24, 2017 #5
    I've also heard that if you are inside a hollow sphere that has uniform density and thickness, you will experience no net gravitational force from the sphere from anywhere within it. I've never bothered to check if this was true though...
     
  7. Apr 24, 2017 #6

    PeterDonis

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    That is correct. More precisely, spacetime inside a hollow sphere is flat. (Note that this is true even if the density of the sphere varies, as long as the variation is purely radial, i.e., as long as everything remains spherically symmetric.)
     
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