Bernouilli's equation comes from requiring conservation of energy in a flowing fluid. It's derived in your textbook. It says that , where is the density and is the height. The second term is related to kinetic energy of the fluid, and the third term is related to gravitational potential energy (near the surface of the Earth): you can see that these terms resemble and for point particles. At two points along a flow, and the pressure difference is related to work done.

You can check the units for each term: they will come out to be (try it).

Kate Scholberg 2015-04-07