The theory that the minuet particles of all matter are in constant motion and that the temperature of a substance is dependent upon the velocity of this motion. Increased motion is accompanied by increased temperature. According to the kinetic theory of gases, elasticity, diffusion, pressure and other physical properties of gasses are due to the rapid motion (in straight lines) of the molecules; to their impact against each other and the walls of the container; to weak cohesive forces between the molecules, etc