Editing Pressure (section)

===Fluid pressure===
''Fluid pressure'' is most often the compressive stress at some point within a [[fluid]].  (The term ''fluid'' refers to both liquids and gases – for more information specifically about liquid pressure, see [[#Liquid pressure|section below]].)
[[File:Defekter unterflurhydrant goettingen.jpg|thumb|upright=1.2|Water escapes at high speed from a damaged hydrant that contains water at high pressure]]
Fluid pressure occurs in one of two situations:
* An open condition, called "open channel flow", e.g. the ocean, a swimming pool, or the atmosphere.
* A closed condition, called "closed conduit", e.g. a water line or gas line.

Pressure in open conditions usually can be approximated as the pressure in "static" or non-moving conditions (even in the ocean where there are waves and currents), because the motions create only negligible changes in the pressure. Such conditions conform with principles of [[fluid statics]]. The pressure at any given point of a non-moving (static) fluid is called the ''hydrostatic pressure''.

Closed bodies of fluid are either "static", when the fluid is not moving, or "dynamic", when the fluid can move as in either a pipe or by compressing an air gap in a closed container. The pressure in closed conditions conforms with the principles of [[fluid dynamics]].

The concepts of fluid pressure are predominantly attributed to the discoveries of [[Blaise Pascal]] and [[Daniel Bernoulli]]. [[Bernoulli's equation]] can be used in almost any situation to determine the pressure at any point in a fluid. The equation makes some assumptions about the fluid, such as the fluid being ideal<ref name=Finnemore>{{cite book |last=Finnemore, John, E. and Joseph B. Franzini |title=Fluid Mechanics: With Engineering Applications |year=2002 |publisher=McGraw Hill, Inc. |location=New York |isbn=978-0-07-243202-2 |pages=14–29}}</ref> and incompressible.<ref name=Finnemore/> An ideal fluid is a fluid in which there is no friction, it is [[inviscid]]<ref name=Finnemore/> (zero [[viscosity]]).<ref name=Finnemore/> The equation for all points of a system filled with a constant-density fluid is<ref name=NCEES>{{cite book |title=Fundamentals of Engineering: Supplied Reference Handbook|year=2011|publisher=NCEES|location=Clemson, South Carolina|isbn=978-1-932613-59-9|page=64}}</ref>
<math display="block">\frac{p}{\gamma} + \frac{v^2}{2g} + z = \mathrm{const},</math>

where:
*''p'', pressure of the fluid,
*''<math>{\gamma}</math>'' = ''ρg'', density × acceleration of gravity is the (volume-) [[specific weight]] of the fluid,<ref name=Finnemore/>
*''v'', velocity of the fluid,
*''g'', [[gravitational acceleration|acceleration of gravity]],
*''z'', elevation,
*<math>\frac{p}{\gamma}</math>, pressure head,
*<math>\frac{v^2}{2g}</math>, velocity head.

====Applications====
* [[Hydraulic brakes]]
* [[Artesian well]]
* [[Blood pressure]]
* [[Hydraulic head]]
* [[Turgor pressure|Plant cell turgidity]]
* [[Pythagorean cup]]
* [[Pressure washing]]