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B Momentum transport in gases in 2d

  1. Sep 14, 2018 #1
    I was trying to understand the momentum transport between gas molecules in 2d.In the image below, it is stated that half of the molecules move up(positive velocity in y direction) and half negative.But the author didnt explain why he assumed it. IMG_20180914_172950.jpeg
     
  2. jcsd
  3. Sep 14, 2018 #2

    anorlunda

    Staff: Mentor

    Because the whole gas mass is assumed to be static, not moving up, down, left, right.

    You could do a different analysis for an upward accelerating gas mass, such as on a rocket, but the answers would change.
     
  4. Sep 14, 2018 #3
    But why half if the gas is static?Please explain.I refered a few books for momentum transport but all of them used tensors.Is there any book(or other source) in which transport is explained only in 2d?
     
  5. Sep 14, 2018 #4

    anorlunda

    Staff: Mentor

    No, all the particles are moving, some + some -, the average speed of all is zero.
     
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