It is an experimental observation of about the behavior of gases, it follows six postulates or assumptions:

1. Gases moves freely, constant motion.
2. Gases moves in a straight line until it collides with another gas or to the container.
3. The volume of the gas is an empty space.
4. There is no force of attraction between the gas particles or between the particles and the wall of container.
5. Gases are perfectly elastic. None of its energy is lost when it collides with another particle.
6. the Average kinetic energy of a gas depends on its Temperature.