Bernoulli  principle, physical principle formulated by Daniel Bernoulli that states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.

If no energy is added to the system, an increase in velocity is accompanied by a decrease in density and/or pressure. The law is directly related to the principle of conservation of energy. 

Bernoulli  Theorem

For a streamline fluid flow, the sum of the pressure (P), the kinetic energy per unit volume (ρv²/2) and the potential energy per unit volume (ρgh) remain constant.

Mathematically:- P+ ρv²/2 + ρgh = constant

where P= pressure ,

E./ Volume=1/2mv²/V = 1/2v²(m/V) = 1/2ρv²

E./Volume = mgh/V = (m/V)gh = ρgh