Molecular thermal motion is the continuous and random movement of molecules and atoms within all matter. This motion never stops and occurs in solids, liquids, and gases. The molecules move randomly in all directions, constantly colliding with each other and changing their paths.
Temperature is directly related to the intensity of molecular thermal motion. When temperature increases, molecules move faster and have more kinetic energy. When temperature decreases, molecular motion slows down. At absolute zero, molecular motion theoretically stops completely.
Molecular motion behaves differently in the three states of matter. In solids, molecules vibrate around fixed positions in a regular pattern. In liquids, molecules have more freedom and can slide past each other. In gases, molecules move completely freely and rapidly in all directions. The intensity of motion increases from solid to liquid to gas.
We can observe evidence of molecular thermal motion in everyday phenomena. Brownian motion shows tiny particles like pollen grains dancing randomly in water due to collisions with invisible water molecules. Diffusion demonstrates how molecules spread from high to low concentration areas. Evaporation occurs when fast-moving molecules escape from liquid surfaces.