Pressure

According to the kinetic theory, gas, like all matter, is composed of many small, invisible particles that are in constant motion. In a child's toy balloon, the amount of particle motion depends on the temperature of the gas trapped inside. The collision of the air particles with the walls of the balloon, accounts for the pressure.

Imagine a glass jar containing a few steel ball bearings. If you were to shake the jar, the steel balls would crash into the walls, and the sum of their forces would exert a pressure which might be enough to break the glass. Pressure depends on the total number of collisions and the intensity of the force with which each steel ball hits the glass. Both factors can be increased by shaking the jar more violently or in the case of the toy balloon, by increasing the temperature of the air trapped inside.