The characteristics of fluids lead up to the thought that the molecules in fluids are in a constant motion and that they knock at each other and at the walls of a vessel.
The motion of molecules is especially expressive in gases. A small density of gases signifies that gas molecules are relatively wide apart from each other. Gas fills up all the space of the vessel and presses on every wall, therefore molecules move in all directions.
From the fact that gas does not occupy the bottom of the vessel we conclude that we can neglect the influence of the weight of molecules on the motion of molecules. Molecules in gases can move so fast that the weight practically does not have any effect.
The motion velocity of molecules depends upon the temperature of gas. The higher the temperature the faster the motion of molecules.
