Gas Laws (Boyles Law)  Engineering Science
What is an ideal gas? There is a strict relationship between pressure, volume and temperature. Boyles law is assuming that an ideal gas is in use.
Boyles Law
Boyles law states that at a constant temperature for a fixed mass, the absolute pressure and the volume of a gas are inversely proportional.
Boyles law takes the following as constants;
Fixed mass of gas
Constant temperature (Isothermal)
P= Pressure
V= Volume
P1 V1 = P2 V2
Example
A gas occupies a volume of 3 m³ at a pressure of 30 MPa
What is the pressure if the volume is expanded to 5 m³?
Ok so to break down what we know from the information above, we know the following;
P1=30 MPa
V1=3 m³
V2=5 m³
So we need to find out what P2 is.
From the equation P1 x V1 = P2 x V2 we can rearrange the formula to give us P2.
P2 = P1 x V1/ V2
Answer: P2 = 18 MPa
Fig: 1 
The graph above (fig:1) shows the relationship between pressure and volume under boyles law, if you multiply the pressure and volume together at any single point on the graph you will always end up with the same value. This proves the absolute pressure and the volume of a gas are inversely proportional when using boyles law.
For example.
3m³ x 30MPa = 90
6m³ x 15MPa = 90
