Two-dimensional ideal gas in a square box simulation. Ideal Gas Expansion model simulates a two-dimensional ideal gas in a square box. 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.

This simulation uses Easy Java Simulations (Ejs) to model a two-dimensional ideal gas in a square box. The particles are initially all on the left (red) side of the box with otherwise random positions and random velocities (distributed according to a Maxwell distribution). One window show an animation of the motion of the particles in the box. Another window shows a plot of the number of particles on each side of the box (red=left, blue=right) as a function of time.
Controls:
1. Play/Pause: starts (or stops) the simulation.
2. Step: advances the simulation by one time step.
3. Reset: resets simulations with initial parameter values.
4. Reverse: reverses the velocity of all particles.
5. Number of Particles: sets the number of molecules in the gas (up to 2000).
6. Show Histogram: checkbox to show a histogram of the number of time steps with a given number of particles on the left side.
7. Speed (fps): slider to control the speed of the simulation, in terms of the number of frames displayed per second. Higher values make the simulation run faster.

You can modify this simulation if you have Ejs installed by right-clicking within the running simulation and selecting Open Ejs Model from the pop-up menu.

In the model, the particles are initially all on the left (red) side of the box with otherwise random positions and random velocities (distributed according to a Maxwell distribution). Separate windows show the motion of the gas particles, a plot of the number of particles on each side versus time, and a histogram of the number of occurrences of a given number of particles on the left. The user can modify this simulation if EJS is installed locally by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu item.

EJS Ideal Gas Expansion 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_IdealGasExpansion.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 re available. They can be found by searching ComPADRE for Open Source Physics, OSP, or EJS.

Requirements:
* Java

The license of this software is Free, you can free download and free use this graphing software.