Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Understanding the effects of gravity on a gas

  1. Aug 29, 2010 #1
    If a gas is enclosed in an insulated container on earth, I understand that at the top of the container there will be less pressure than at the bottom due to gravity.

    What I want to know is if the top is colder due to the effects of gravity. If reliable sources could provided it would be appreciated (I can't seem to find any).
  2. jcsd
  3. Aug 29, 2010 #2
  4. Aug 29, 2010 #3
    Can you go into it any more than just simply 'no' curl, as to why?
  5. Aug 29, 2010 #4
    The kinetic theory of gases describes the atoms or molecules of a confined gas as having a random distribution of the x,y and z components of velocity, and they move in straight lines until they collide with the container walls and bounce off. That description leads to a mixing that would have the population of molecules in any region of the container having the same average kinetic energy as the molecules in any other region of the container.

    To produce the difference in pressure between the top and bottom due to gravity, change the reference to motion in straight lines into a reference to motion in parabolas that are very nearly straight lines. This makes the density and pressure slightly less at the top. Whether that causes a slight temperature gradient, I don't remember.
  6. Aug 30, 2010 #5

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Wrong. The answer is yes. First off, Wikipedia is not a reliable source, and secondly that wiki article doesn't say anything about the question being asked.

    Lots of people go to the mountains in the summer to escape the heat. Think about that for a second.

    Google the phrase "lapse rate".
  7. Aug 30, 2010 #6
    Mikelepore, My own consideration of what occurs within the gas regarding a possible heat difference; that heat is related to the kinetic energy of the molecules that make up the gas, with that kinetic energy being converted to gravitational potential energy if a molecule moves against the force of gravity.

    D H, Curl may have read my other thread, "the altitude hypothesis" which brings about a particular dilemma based on this. The thread eventually came to a halt when I asked about lapse rate.

    The hypothesis has two parts and what i was expecting was that the latter part to be the shortcoming. The users that posted opted for the first part as being the problem. That being a heat gradient does not emerge in contained body of gas under gravitational force.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook