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

Mechanical roots of irreversible processes

  1. Dec 28, 2009 #1
    In trying to understand the underlying mechanics of irreversible processes, I came up with four mechanical asymmetries that seemed relevant to describe energy transfer through the bulk motion of a frictionless piston that divides a cylinder with two gasses of same pressure but different temperature.

    1)Energy transfer depends on the direction of the piston’s motion and particles gain more energy from an advancing piston than they lose from a receding piston. The asymmetry is independent of the molecular energy.

    2)Fast particles lose more energy in the recoil of the piston than do slow ones. This also ensures piston motion, enabling the other three asymmetries.

    3)The piston’s motion modulates the arrival rate of the particles (greater arrival rate when the piston is advancing).

    4)For very fast moving pistons in a gas, the state of the gas near the piston surface is also modulated by the piston motion, increasing the arrival rate modulation.

    For now I’m assuming that we have used other means to know the velocity distribution of the molecules and the piston. Using the mechanics described we could find the energy transfer for any combination of piston velocity and molecular velocity, and assuming that there those velocities are not correlated, I could add up all the energy transferred through the piston. So I was wondering if this should correctly lead to the energy transfer or if I was missing something or totally in error. (I may have made mistakes when I tried it).

    I put more detail about it in the three files (an overview, a narrative, and drawings) at

    http://groups.google.com/group/foa_group/files [Broken]

    It’s in part 1 of “Entropy Concepts” – mostly in sections 1.1, 1.6., and 1.12. But the early parts of this is working with the simpler case of particle beams against the piston, trying to show that for specific sequences or particle arrival, energy can be made to flow from a “cold” beam to a “hot” beam. But when the beams are random, most sequences transfer heat in the normal direction. Then it goes on to monatomic gasses.
    Last edited by a moderator: May 4, 2017
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted