The kinetic molecular theory explains the behavior of gases based on the idea that they are made up of tiny particles in constant motion. These particles move randomly and collide with each other and the walls of their container. The energy of these collisions determines the temperature of the gas; higher energy means higher temperature. According to this theory, the distance between gas particles is much greater than their size, allowing them to spread out and fill any available space. This explains why gases can be compressed and why they expand to occupy the volume of their container, such as in a balloon or soda can.