Animation showing the behaviour of an ideal gas. The gas is composed of grey particles with a range of velocities. The dials at right show pressure P, temperature T and volume V. In an ideal gas, changes in any one of those three variables has a proportional effect on the others. The ideal gas law states that, all other things being equal, the temperature of a gas is proportional to the product of its volume and pressure. See animations K003 3526_3530 for demonstrations of these principles.