This pressure generates a force acting from the inside of the liquid outwards and perpendicular to all the walls of the container. Another important property of a fluid at rest is that the force due to its pressure always acts perpendicular to any surface that is in contact with it.

All the liquids exert pressure on the base or bottom and walls of their container. All the liquid have weight. When we pour liquid into a vessel, then the weight of liquid pushes down on the base of the vessel producing a pressure. The liquid exerts pressure on the base of the vessel.

Hydraulics use fluid pressure to create the same mechanical advantage as a lever. The Bernoulli Principle allows airplanes to fly from the lift created by reduced air pressure on the top of their wings. Fluids also can be used to reduce friction.

Note that pressure P has units of energy per unit volume, too. Since P = F/A, its units are N/m2. If we multiply these by m/m, we obtain N ⋅ m/m3 = J/m3, or energy per unit volume.

Liquids are relatively incompressible because any increase in pressure can only slightly reduce the distance between the closely packed molecules. If the pressure above a liquid is increased sufficiently, the liquid forms a solid. If the pressure above a liquid is decreased sufficiently, the liquid forms a gas.

A high pressure system has higher pressure at its center than the areas around it. Winds blow away from high pressure. Swirling in the opposite direction from a low pressure system, the winds of a high pressure system rotate clockwise north of the equator and counterclockwise south of the equator.

A high pressure system is a whirling mass of cool, dry air that generally brings fair weather and light winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere. These bring sunny skies.