Pressure is one of two fundamental quantities describing fluid (hydraulic) processes. It corresponds closely to what we mean by it in everyday life. If we are submersed in a fluid, the fluid presses upon our surface from all sides.

Pressure is equivalent to the potential of fluids (hydraulic potential), pressure differences are driving forces for different processes: by itself, a fluid flows from points where the pressure is high to points where it is lower.

The isotropic part of the momentum current density tensor (mechanical stress tensor).

p, (P)

Liquid at rest in a gravitational field (hydrostatic pressure):

     p(h) = rho*g*h + p_a

rho: density of liquid, g: gravitational field, h: depth below surface, p_a: ambient pressure (air pressure at liquid surface)

Pressure of an ideal gas:

     p*V = n*R*T

V: volume of gas, n: amount of substance, R: universal gas constant, T: (absolute) temperature

[p] = Pa (Pascal), Pa = N/m^2; 1 bar = 10^5 Pa, 1 mmHg = 133 Pa

hydraulic or fluid potential, hydraulic level

pressure difference, ambient pressure, hydrostatic pressure, pressure force

The pressure at the bottom of a 10 m column of water is about 1 bar; it is roughly the same as the pressure of the atmosphere at sea level.

Ambient pressure: Pressure of the environment, often the pressure of the surrounding air.

Druck