See also: Archimedes' Principle; Hydraulic Machinery
Ratio of the Force acting on a surface to the area (see Area - Circle, Area - Rectangle) of the surface. A fluid (liquid or Gas - see States Of Matter) exerts a pressure on all bodies immersed in it. For a fluid at rest, the
difference in pressure between two points in it depends upon only the Density of the fluid and the difference in depth or altitude between the two points.
Atmospheric pressure is measured with a Barometer. Other instruments for measuring pressure are commonly termed pressure
gauges; they include the Bourdon gauge and the manometer.