[The sum of the energies: pressure , kinetic (velocity) and potential at one point is equal to any other point in the stream].
where 
is the mass of fluid considered,
is the density of the fluid,
and 
are the pressure, speed and height at one point in the stream,
and 
are the pressure, speed and height at another point.
What Bernoulli's equation really says is that fluid flow has three forms for its energy and that as long as that fluid flow flows smoothly and without significant friction through a system of stationary obstacles, the sum of those three energies can't change. The three energies are kinetic energy (the energy of motion), gravitational potential energy, and an energy associated with pressure that may be called pressure potential energy. The obstacles must remain stationary so that they can't do work on the fluid flow and thus change its total energy. Since the sum of those three energies doesn't change as fluid flow flows through a stationary environment, its pressure typically falls whenever its speed rises and vice versa. If the fluid flow also changes altitude significantly, then gravitational potential energy must be included in these energy exchanges.
