The kinetic theory says that the particles that make up all matte are in constant motion. A gas is composed of particles. These particles have little volume and are far from one another with empty space between them. There are no attractive or repulsive forces between these particles. The particles in a gas move rapidly in constant random motion.
All collisions are perfectly elastic.
Perfectly elastic means that E is transferred from one particle to another during collisions but the total KE remains constant. The physical behavior of a gas depend on its volume, temperature and pressure. Gases not in a sealed container are uncontained gases. Because gas particles are in motion, they kinetic energy. An increase in the T of a substance means an increase in the avg KE of the particles of the substance.