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

Do gas molecules align with gravity?

  1. Oct 8, 2008 #1
    In a gas, do the molecular centers of gravity align significantly toward the dominant source of gravity? E. g., do atmospheric water vapor molecules tend to have their oxygen atoms facing Earth's center?
  2. jcsd
  3. Oct 8, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It's interesting to consider the energy penalty of a water molecule being "upside down"; that is, with the oxygen atom on top. When I multiply the mass of an oxygen molecule by the force of gravity by the difference in height between the two configurations, I get about 10-35 J. I'll leave it to you to compare that with the average rotational energy of a water molecule to determine if gravity has any considerable influence on orientation.
  4. Oct 8, 2008 #3
    My initial guess is that such a molecule would have the average rotational energy of kT/2=10-35 J. So T=10-12 K, about the current limit of cryogenic technology. The influence is negligible.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?