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Forces on a falling sphere in a liquid

  1. Sep 27, 2010 #1
    I want to design a model for falling spheres in a Newtonian fluid and I just want to make sure I've got everything right. Are these all of the forces that apply on an object in a liquid?


    I have the following formulas:

    [URL]http://upload.wikimedia.org/math/7/2/2/722eecf17cc922626c36f3488ca290e9.png[/URL] (Stokes' drag)
    [URL]http://upload.wikimedia.org/math/4/c/b/4cbadb68d4f9eade03797f90f99eae0a.png[/URL] (Buoyancy)
    [URL]http://upload.wikimedia.org/math/e/5/1/e51111b22ad80b2b72ef52dccc810409.png[/URL] (Gravity)
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Sep 27, 2010 #2
    Yes but be careful.
    The V in the first equation is the velocity of the falling sphere, but in the second it's the volume of it.
  4. Sep 28, 2010 #3
    Yes, dont forget that if the sphere size is comparable with the gap between the air molecules then you will have to make a correction for stokes law based on Robert Millikians Oil Drop experiment
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