Throughout this applet they are developing a powerful and general approach to educational software: computer simulations that allow students to interact with different components of a complex real world phenomenon.
The simulation shown here is of a 4-stroke internal combustion engine. The thermodynamic cycle being simulated is the Otto cycle, which involves an isentropic compression, an explosion at constant volume, an isentropic expansion, and the release of the exhaust at constant volume to return to the original pressure.