Why are the molecules of gases always moving?

Molecules in air are constantly moving and hitting the dust particles. Because the molecules are moving in many directions, they collide with the dust particles from different directions. This action causes the darting motion of the dust that you observe. Atoms and molecules are always in motion. read more

The average kinetic energy of a gas particle is directly proportional to the temperature. An increase in temperature increases the speed in which the gas molecules move. All gases at a given temperature have the same average kinetic energy. Lighter gas molecules move faster than heavier molecules. read more