Pressure should decrease in zero gravity?

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Discussion Overview

The discussion revolves around the behavior of gas pressure in a closed container when subjected to zero gravity conditions. Participants explore the implications of gravity on pressure distribution, the kinetic theory of gases, and statistical mechanics, examining whether pressure should decrease in the absence of gravitational force.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that pressure should decrease in zero gravity because gravitational force is not pulling gas molecules, leading to less momentum transfer and thus lower pressure.
  • Another participant points out that under gravity, pressure in a container is not uniform, indicating that the pressure gradient is affected by the gravitational field.
  • Some participants agree that while average pressure remains the same, the distribution of gas molecules changes due to gravity, creating localized regions of higher and lower density.
  • There are calls for modeling the situation quantitatively, with references to variables such as the number of moles, molecular weight, and the Boltzmann distribution to analyze pressure in a gravitational field.
  • Statistical mechanics is proposed as a method to derive pressure values at different heights within the container, suggesting a more complex relationship than initially considered.

Areas of Agreement / Disagreement

Participants express differing views on the impact of gravity on pressure in a gas container. While some agree that average pressure remains constant, others emphasize the importance of pressure gradients and the redistribution of gas molecules under gravitational influence. The discussion does not reach a consensus on the effects of zero gravity on pressure.

Contextual Notes

Participants note the limitations of their assumptions, such as the dependence on the definitions of pressure and the conditions under which the analysis is performed. The discussion includes unresolved mathematical steps and varying interpretations of the kinetic theory and statistical mechanics.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, kinetic theory, statistical mechanics, or anyone curious about the effects of gravity on gas behavior in closed systems.

Ravi Singh choudhary
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Pressure can exist in a container of gas even if there is no gravity. From kinetic theory of gases it is assumed that pressure exists due to momentum transfer between molecules and the wall. Suppose I have a closed container on Earth at sea level filled with air. Now I carried it to zero gravity facility. I maintained all other thermodynamic parameter like volume and temperature. Now pressure should decrease as gravitational force is not pulling individual gas molecules. Therefore there should be less momentum of particles so the pressure. Please just give me insight to my thought whether I am current or not?
 
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Under gravity, the pressure in the container is not uniform... usually the effect is small but in large containers (ie the atmosphere) the effect is quite obvious.
 
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I agree with @Simon Bridge. The average pressure should be the same. The difference will only be the vertical pressure gradient.
 
Why don't you just model it and figure it out yourself? Let n be the number of moles in the container and M be the molecular weight. Let's see your analysis.
 
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Chestermiller said:
Why don't you just model it and figure it out yourself? Let n be the number of moles in the container and M be the molecular weight. Let's see your analysis.

Total mass is always nM, now when container is influenced by gravity some molecules will drift downward and localised higher density region is created opposite what we had uniform density region. Now more number of collisions is there in the downward region while less number of collisions in upward region. So average pressure remains same but molecules are just redistributed in gravity.
 
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Ravi Singh choudhary said:
Total mass is always nM, now when container is influenced by gravity some molecules will drift downward and localised higher density region is created opposite what we had uniform density region. Now more number of collisions is there in the downward region while less number of collisions in upward region. So average pressure remains same but molecules are just redistributed in gravity.
I meant to analyze the problem quantitatively. Assume you have a vertical cylinder of cross sectional area A and height h.
 
This is most simply solved by statistical mechanics. Just write down the Boltzmann distribution!
 
vanhees71 said:
This is most simply solved by statistical mechanics. Just write down the Boltzmann distribution!
This sounds interesting. With gravity switched on, using statistical mechanics, what do you get for the pressure at the top of the container, the pressure at the bottom of the container, and the average pressure (in terms of A, M, n, h, g, R, and T)?
 

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