Bernoulli's Principle
It states that as the speed of a moving
fluid (liquid or gas) increases, the pressure within the fluid
decreases. The phenomenon described by Bernoulli's principle has many
practical applications. Bernoulli's principle thus says that a rise
(fall) in pressure in a flowing fluid must always be accompanied by a
decrease (increase) in the speed, and conversely, if an increase
(decrease) in , the speed of the fluid results in a decrease (increase)
in the pressure.
Bernoulli's principle can be explained in terms of the
law of conservation of energy. As a fluid moves from a wider pipe into a
narrower pipe or a constriction, a corresponding volume must move a
greater distance forward in the narrower pipe and thus have a greater
speed. At the same time, the work done by corresponding volumes in the
wider and narrower pipes will be expressed by the product of the
pressure and the volume. Since the speed is greater in the narrower
pipe, the kinetic energy of that volume is greater. Then, by the law of
conservation of energy, this increase in kinetic energy must be balanced
by a decrease in the pressure-volume product, or, since the volumes are
equal, by a decrease in pressure.