Bernoulli's equation
It describes conservation of energy in the steady flow of an ideal fluid, linking pressure, velocity and height.
General form
Variables
Symbol
Meaning
p
static pressure of the fluid
ρ
fluid density
v
flow velocity
g
gravitational acceleration
h
height
Applications
Fluid draining from a tank (Torricelli's law)
When fluid drains from an open tank, the pressure at the surface and at the outlet equals atmospheric pressure. The velocity at the surface is roughly 0. Bernoulli's equation simplifies to $v = \sqrt{2gh}$.
Venturi tube
When fluid flows through a narrowing in a pipe, the velocity rises (continuity equation) and the static pressure drops as a result. This is used to measure flow rate.