# Poiseuille’s Law | Definition, Formula – Hydrodynamics

Poiseuille’s Law Definition:
The law of Poiseuille states that the flow of liquid depends on the following variables such as the length of the tube(L), radius (r), pressure gradient (∆P) and the viscosity of the fluid (η) in accordance with their relationship.

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## Poiseuille’s Law | Definition, Formula – Hydrodynamics

Poiseuille’s Law Formula:
The rate of flow (u) of liquid through a horizontal pipe for steady flow is given by

v = $$\frac{\pi}{8} \frac{p r^{4}}{\eta l}$$

where,
p = pressure difference across the two ends of the tube,
r = radius of the tube,
η = coefficient of viscosity,
l = length of the tube.

Hydrodynamics:
In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.