Boyle's law

The pressure of a gas increases when you squeeze it into a smaller volume. Using the apparatus shown, you can investigate exactly how the pressure relates to the volume.

Careful experiments show that, for most gases, the pressure of a fixed mass of gas at a constant temperature multiplied by its volume is always constant.

PV = constant

This is known as Boyle's law. It can be written as:

P = constant
       V

or

P1V1 = P2V2

For a gas that obeys Boyle's law, a graph of P against 1/V is a straight line.