The Molecular Dynamics Adiabatic Piston model shows two gas samples within a horizontal cylinder that is divided by an insulated piston that moves without friction.   It is a supplemental simulation for an article by  Eric Gislason "A close examination of the motion of an adiabatic piston" in the Am. J. Phys. 78 (10), 995-1001 (2010).  Initially the piston is held (locked) in place, and the pressures of the gases on each side of the piston are different.  When the piston is released it undergoes oscillations that are damped due to collisions of the particles with the piston, and it finally ends up at rest.  The final pressures of the two gases are equal, but the final temperatures are typically different.

All particles in the Molecular Dynamics Adiabatic Piston model have unit mass and interact through pairwise Leonard-Jones forces.  Gas particles interact with the container walls via a spring (Hooke's law) force and this particle-wall interaction is used to move the piston and to compute the pressure.  The temperature is computed from the average kinetic energy. The piston position and the temperature and pressure are shown as functions of time in additional windows.

The Molecular Dynamics Adiabatic Piston 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_md_AdiabaticPiston.jar file will run the program if Java is installed.

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