Pressure

Pressure, force acting on a surface per unit of area. All liquids and gasses exert pressure on any body immersed in them and on the walls of their containers, if any. According to the kinetic theory of matter, the pressure in a closed container of gas arises from the bombardment of the container walls by gas molecules: it is proportional to the temperature and inversely proportional to the volume of the gas.

See also: Physics.