head> Collapsible Dropdown Menus

Hover over the menu bar to pick a physics animation.

Gas Expansion against a moving Piston

Please click for a full description of this subject Here the gas expands because an external force moves a piston so that the gas can occupy a larger volume. This means that the gas atoms give up energy to the piston but we will assume here that piston temperature does not increase. The time-dependent total atomic energy (proportional to absolute temperature) is shown in black and the gas pressure is shown in green. The smooth blue curve shows the energy expected from first principles. The expression for energy Vs piston position that seems to fit best is: `E/E0=(x_(P0)/x_P)^(3/2)` where `x_(P0)` is the initial piston position and `x_P` is its present position. The piston expands and contracts the gas. If the piston speed is low enough, it is seen that the energy Vs piston position is almost reversible. If the piston speed is faster, then the process is not reversible because the atoms near the piston do not have enough time to restore to their equilibrium of static energy distribution. The learner may (within limits) use the Sliders to change the following variables: 1. Initial average speed of atoms 2. Radius of atoms 3. Total Number of Atoms 4. Piston Speed 5. Expansion ratio 6. Gas equilibration time before starting piston