The EJS Ideal Gas with Maxwell's Demon model simulates a two-dimensional ideal gas in a square box, monitored by Maxwell's Demon (which allows only faster than average particles to move from the right side to the left side, while allowing only slower than average particles to move the other way).   This simulation can be used as part of the activity described in "The Statistical Interpretation of Entropy: An Activity" by Todd Timberlake, to be published in The Physics Teacher.

In the model, the particles are initially spread throughout the box with random positions and random velocities (with a Maxwell distribution of speeds). One window shows an animation of the motion of the particles in the box, while another window plots the temperature of the gas on each side of the box as a function of time.  The user can turn the Demon on/off, or reverse the velocities of all particles.  You can modify this simulation if you have EJS installed by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu item.

EJS Ideal Gas with Maxwell's Demon model was created using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.   Double clicking the ejs_entropy_IdealGasMaxwellsDemon.jar file will run the program if  Java is installed.  EJS is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models.  Additional EJS models are available.  They can be found by searching ComPADRE for  Open Source Physics, OSP, or EJS.

Please note that this resource requires at least version 1.5 of Java (JRE).