Bernoulli's equation It applies to steady flow of incompressible fluid. By steady flow we mean that at any one place in the fluid the velocity never changes. (Also known as streamline flow). According to this equation, which is derived from the law of conservation of energy, the quantity

p + r g h + (1/2) r v² =constt

at all points in the motion of such a fluid. Where p is the absolute pressure, h the height above an arbitrary reference level, and v the fluid velocity, and r the density of the fluid.

Another form of Bernoulli's equation is obtained by dividing each term of the above equation by r g.

p/(r g) + h + v²/(2g) = constt.

Each term of this equation has dimension of length and is called head. p/r g is the pressure head, v²/2g, velocity head and h, elevation head.