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Fluid Dynamics -- a spherical particle immersed in water

  1. Oct 31, 2017 #1
    • New user has been reminded to show the Relevant Equations snd show their initial work on the solution
    1. The problem statement, all variables and given/known data

    Consider a spherical particle immersed in water. It will experience random collisions with the surrounding water molecules. Suppose there are such water molecules around the particle. Half (n/2) of the water molecules will push the particle to the right and the other half to the left. On average, this “collision force” (force arising from collisions) vanishes. Does this mean that the particle will not be driven to the right or to the left?

    2. Relevant equations
    not sure

    3. The attempt at a solutiIn
    I know the particle will move. But I am not sure how to explain that using equations.
  2. jcsd
  3. Nov 1, 2017 #2


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    Gold Member

    I have the following questions:

    1. Is the spherical particle contained in a tank/beaker/vessel?
    2. What is the size of the particle comparing to the tank's size?
    3. Is the particle immersed in the middle or near the walls of the tank?

    How do you know that the particle will move?
  4. Nov 1, 2017 #3
    This is kind of like a problem in flipping coins. Even though a coin turns up heads half the time and tails half the time, that does not mean that the cumulative number of heads cannot be greater than the cumulative number of tails at any given time.
  5. Nov 1, 2017 #4
    Sir, we are not informed about any of those situations.
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