Bernoulli's principle

Bernoulli's principle (or Bernoulli's equation) is a formula that relates the height, density, pressure, and velocity of a non-viscous and non-conducting fluid. It states that
:p\, +\, \rho\, g\, h\, +\, \tfrac12\, \rho\, v^2\,=\, \text{constant}\,
p is the pressure, ρ is the density, h is the elevation, v is the velocity of the fluid, and g is acceleration due to gravity.
==Derivation==
Since total energy in a system is conserved,
:W + E_p + E_k = \text{constant}
Work is equal to force times distance. Since pressure is force divided by area and distance is velocity times time, we get
:W = Fd = \frac{F}{a} a\, v\, t\, = p\, a\, v\, t\,
Since area times velocity times time is equal to volume, we can rewrite this as mass over density, giving
:W = \frac{p\, m\,}{\rho}
The potential energy will be equal to
:m\, g\, h\,
and the kinetic energy will equal
:\tfrac12\ m\, v\, ^2
By substituting these values in, we get
:\frac{p\, m\,}{\rho} + m\, g\, h\, + \tfrac12\ m\, v\, ^2 = \text{constant}
This can be simplified by dividing both sides by m and multiplying by ρ, giving
:p\, + \rho\, g\, h\, + \tfrac12\ \rho\, v\, ^2 = \text{constant}
Category:Fluid mechanics