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Bernoulli's Principle
"For an ideal fluid, an increase in the flow velocity of the fluid is coupled with a decrease in its pressure."
Bernoulli's principle is the result of the law of conservation of energy. The sum of the static pressure exerted by a fluid and its dynamic pressure (which is related to its speed, or velocity) must be constant. Therefore an increase in one factor must be balanced by a decrease in the other. This can be expressed by the equation:
p + q = constant
where p is static pressure and q is dynamic pressure.
Air can be considered a fluid with no viscosity, and can also be considered to be incompressible at low speed. To account for higher mach numbers, more complex forms of Bernoulli's principle must be used.
Application
Bernoulli's principle is used with Newton's laws of motion to describe how an aerofoil generates lift.