**Pressure volume diagrams ****06/13/16**

*“How can we empirically model the change in pressure and volume of a gas?”*

In order to model the change in pressure and volume of a gas, Scientists and Engineers have created a framework known as **Pressure volume diagrams. **P-V diagrams are very simple, the Pressure and volume of an object will be represented by a cartesian coordinate system with the Pressure on the vertical axis and the Volume on the horizontal. When work is added to the system, the change in volume and pressure is recorded along an arc length. The volume under this curve represents the **change in work** in the system. The return process does not have to be symmetric, so often a P-V diagram could possibly have a different return curve.

Let us illustrate with the following example. Imagine gas with a piston in a machine.The state of the gas gas starts at point 1 on the graph. Heat is then added, which the increase the pressure. The normalization process then starts, which decreases the pressure and increases the volume, causing the state to go to poin 2. Heat is then extracted, which causes the state to go to point 4, and the reverse normalization process starts, which causes everything to go back to the begining at point 1.