# Equation of Continuity | Definition, Derivation – Hydrodynamics

Equation of Continuity Physics:
If a liquid is flowing in streamline flow in a pipe of non-uniform cross-sectional area, then rate of flow of liquid across any cross-section remains constant.

A continuity equation in physics is an equation that describes the transport of some quantity. It is particularly simple and powerful when applied to a conserved quantity, but it can be generalized to apply to any extensive quantity.

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## Equation of Continuity | Definition, Derivation – Hydrodynamics

Equation of Continuity Derivation:
i.e. a1v1 = a2v2 ⇒ av = constant
or
a ∝$$\frac{1}{v}$$ The velocity of liquid is slower where area of cross-section is larger and faster where area of cross-section is smaller. The falling stream of water becomes narrower, as the velocity of falling stream of water increases and therefore its area of cross-section decreases. Deep water appears still because it has large cross-sectional area.

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.