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What is meant by pressure being a momentum flux?

  1. Jul 17, 2014 #1
    hi, I have been working on equation of state and one of my article says pressure is a momentum flux. what is the physical meaning of this? they have written it as

    pressure =(1/3) *number density*volume*momentum

    please explain me the expression

  2. jcsd
  3. Jul 20, 2014 #2
    I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
  4. Jul 21, 2014 #3
    no not yet, how is pressure a momentum flux?
  5. Jul 21, 2014 #4


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    Staff: Mentor

    A flux of something has units of something per m2 per second: something / (m2·s).

    So momentum flux would be (kg·m/s) / (m2·s). I'll let you simplify it.

    Pressure is force per unit area: N/m2. Expand the newtons into basic units, simplify, and compare with the units of momentum flux.
  6. Jul 21, 2014 #5


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    Science Advisor
    Gold Member

    force is a momentum transfer rate:
    momentum / time

    pressure is force density :
    force / area
    momentum / time / area
  7. Jul 21, 2014 #6


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    Staff: Mentor

    Assuming that "number density" means something like "molecules per m3" and "momentum" means "momentum per molecule", the units are not consistent in this equation. I think "volume" should be "velocity", i.e. you have mis-interpreted a "v" in the original equation.
  8. Jul 22, 2014 #7
    thank u all.
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