12.5 The Kinetic Theory of Gases Kinetic Theory

Explanation: This Java applet simulates a 2-dimensional gas of hard spheres. It illustrates several important concepts in statistical mechanics/kinetic theory, such as: the approach to thermal equilibrium and the Maxwell-Boltzmann speed distribution as discussed in Section 12.5. The "molecules" do not interact except when they come in contact; then they scatter elastically. The small box on the right shows the distribution of speeds as the collisions take place. The blue line is the theoretical result for an ideal gas in thermal equilibrium--a two dimensional Maxwell-Boltzmann distribution, the two dimensional equivalent to the ones shown in Figure 12.11. Left to itself, the simulation will run for a long time; you will probably want to click "Stop" at some point. After the animation stops, you can check the microscopic reversibility of this system by clicking on "Reverse." This flips around all the velocities of the particles and runs the system for a time equal to the time it had run previously. In principle, that should "undo" every collision and restore the initial distribution of positions and velocities. You can see how roundoff error prevents this from happening after a sufficiently large number of collisions per molecule have taken place.

Source: Julio Gea-Banacloche, Dept. of Physics, University of Arkansas at Fayetteville