In general, pressure is a measure of the force exerted per unit area on the boundaries of a substance. In fluid dynamics, many authors use the term static pressure in preference to just pressure to avoid ambiguity. The term static pressure is identical to the term pressure and can be identified for every point in a fluid flow field.
Static pressure is one of the terms of Bernoulli’s equation:
Bernoulli’s effect causes the lowering of fluid pressure (static pressure – p) in regions where the flow velocity increases. This lowering of pressure in a constriction of a flow path may seem counterintuitive but seems less so when you consider the pressure to be energy density. In the high-velocity flow through the constriction, kinetic energy (dynamic pressure – ½.ρ.v2) must increase at the expense of pressure energy (static pressure – p).
The simplified form of Bernoulli’s equation can be summarized in the following memorable word equation:
static pressure + dynamic pressure = total pressure (stagnation pressure)
Total and dynamic pressure are not pressures in the usual sense – they cannot be measured using an aneroid, Bourdon tube or mercury column.
