Editing Bernoulli's principle (section)

=== Simplified form ===
In many applications of Bernoulli's equation, the change in the {{mvar|ρgz}} term is so small compared with the other terms that it can be ignored. For example, in the case of aircraft in flight, the change in height {{mvar|z}} is so small the {{mvar|ρgz}} term can be omitted. This allows the above equation to be presented in the following simplified form:
<math display="block">p + q = p_0</math>
where {{math|''p''<sub>0</sub>}} is called '''''total pressure''''', and {{mvar|q}} is '' [[dynamic pressure]]''.<ref>{{cite web|title = Bernoulli's Equation| publisher = NASA Glenn Research Center| url =http://www.grc.nasa.gov/WWW/K-12/airplane/bern.htm| archive-url =https://archive.today/20120731182454/http://www.grc.nasa.gov/WWW/K-12/airplane/bern.htm| url-status =dead| archive-date =2012-07-31|access-date = 2009-03-04 }}</ref> Many authors refer to the pressure {{mvar|p}} as static pressure to distinguish it from total pressure {{math|''p''<sub>0</sub>}} and dynamic pressure {{mvar|q}}. In ''Aerodynamics'', L.J. Clancy writes: "To distinguish it from the total and dynamic pressures, the actual pressure of the fluid, which is associated not with its motion but with its state, is often referred to as the static pressure, but where the term pressure alone is used it refers to this static pressure."<ref name="Clancy1975" />{{rp|at= § 3.5}}

The simplified form of Bernoulli's equation can be summarized in the following memorable word equation:<ref name="Clancy1975" />{{rp|at= § 3.5}}
{{block indent | em = 1.5 | text = Static pressure + Dynamic pressure = Total pressure.}}

Every point in a steadily flowing fluid, regardless of the fluid speed at that point, has its own unique static pressure {{mvar|p}} and dynamic pressure {{mvar|q}}. Their sum {{math|''p'' + ''q''}} is defined to be the total pressure {{math|''p''<sub>0</sub>}}. The significance of Bernoulli's principle can now be summarized as "total pressure is constant in any region free of viscous forces". If the fluid flow is brought to rest at some point, this point is called a stagnation point, and at this point the static pressure is equal to the [[stagnation pressure]].

If the fluid flow is [[irrotational flow|irrotational]], the total pressure is uniform and Bernoulli's principle can be summarized as "total pressure is constant everywhere in the fluid flow".<ref name="Clancy1975" />{{rp|at=Equation 3.12}} It is reasonable to assume that irrotational flow exists in any situation where a large body of fluid is flowing past a solid body. Examples are aircraft in flight and ships moving in open bodies of water. However, Bernoulli's principle importantly does not apply in the [[boundary layer]] such as in flow through long [[Pipe flow|pipes]].