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Error in Wikipedia Cavendish article

  1. Sep 18, 2015 #1
    According to Wikipedia, Cavendish was able to measure a force of 1.74E-7 N or “roughly the weight of a large grain of sand[13] of 0.13 mg”

    However, with my calculations using m=F/g, where g=9.81m/s/s

    Gives m=1.74E-7/9.81 = 1.77E-8 kg = 0.0177 mg

    Which is much less than 0.13 mg

    Am I missing something?
  2. jcsd
  3. Sep 18, 2015 #2


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    Staff Emeritus
    Science Advisor

    Let's see...

    0.13 mg = 0.00013 g = 0.00000013 kg = 1.3x10^-7 kg
    F = MG
    F = 1.3x10^-7 * 9.81
    F = 1.28x10^-6 Newtons

    Hmm... you appear to be correct.
    Perhaps it should be a small grain of sand?
  4. Sep 18, 2015 #3
    Indeed, the Wikipedia weight is 7.3 times higher.
    I find it impossible that Cavendish was able to measure such a tiny force of attraction between the metal spheres and this force was able to overcome the air resistance and mechanical friction which was apparent in the apparatus.
  5. Sep 19, 2015 #4
    What air resistance and mechanical friction?
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