All courses › Foundations of Physics › Pressure in a liquid

Pressure in a liquid

The pressure in a liquid at rest increases with depth, because each column of liquid must support the weight of everything above it. The gauge pressure is the pressure from the liquid alone, while the absolute pressure also includes the atmospheric pressure at the surface. Pressure acts equally in all directions at a given point.

p = p_0 + \rho gh

pressure at depth h (absolute pressure)

p_{gauge} = \rho gh

gauge pressure from the liquid alone

Symbols

$p_0$	pressure at the surface (often $p_{atm}$ )	Pa
$\rho$	density	kg/m³
$h$	depth	m

Example

A diver is $h = 10$ m below the surface. The gauge pressure is $\rho gh = 1000\cdot 9.81\cdot 10 \approx 98.1$ kPa, so the absolute pressure is $101.3 + 98.1 \approx 199.4$ kPa.

The pressure in a liquid depends only on the depth, not on the shape or total volume of the container.

Practise pressure, density and heat for free →

← Density · Buoyancy →

Part of Foundations of Physics: Pressure, density and heat.