Momentum transport in gases in 2d

  • Thread starter Mohankpvk
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  • #1
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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
 

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  • #2
anorlunda
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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.
 
  • #3
102
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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.
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?
 
  • #4
anorlunda
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But why half if the gas is static?

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

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