The kinetic theory of gases was developed in the 19th century. It is a way to explain and describe the macroscopic behavior of gases. It treats all gases as ideal gases. They are made up of tiny particles (molecules) that are in constant motion. The particles are treated as perfect spheres and the collisions are according to the laws of classical mechanics. There are also no intermolecular forces between the gas particles. These particles are constantly colliding with each other and with the walls of the container holding the gas. These collisions produce the pressure that the gas exerts on the container. As a result, the particles have a kinetic energy which is highly dependent on the temperature of the gas.