Talk:Bernoulli's principle/Temp
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Bernoulli's principle in a fundamental concept in fluid dynamics. At its simplest, Bernoulli tells us that when an incompressible fluid flows in a horizontal tube of varying cross section, the fluid's velocity changes. A change in velocity is called "acceleration", and (as we know from Newton's second law) acceleration only occurs through the action of a force. When a force acts over an area, it is called "pressure". So any change in a fluid's velocity must be matched by a change in pressure (force). This leads us to Bernoulli's observation that the velocity of flow in a tube varies inversely from the pressure against the side of the tube.
The photo shows a simple experimental demonstration of this concept. The air flowing through the larger section of the tube has a higher static pressure than the narrower section. For a steady flow, the amount of fluid entering the pipe must equal the amount leaving the pipe, so the velocity in the narrower section must be higher.
The full version of Bernoulli's principle includes both the work performed by the pressure and by the changes in potential energy resulting from any changes in height. In this form, the principle states that the sum of the pressure, kinetic energy, and potential energy is a constant. (Bernoulli does not take into account viscosity or compressibility.)
[edit] New lead-section text (10 April 2008)
In fluid dynamics, Bernoulli's principle relates, for two points along a streamline, the difference in pressure to the differences in kinetic, potential and internal energy of the fluid flow. Such a relationship is denoted as Bernoulli's equation, of which different specific forms exist for different types of flow[1]. Bernoulli's principle is named in honor of Daniel Bernoulli.
At its simplest, for an incompressible and inviscid flow through a horizontal tube of varying cross section, Bernoulli's equation states that the sum of the pressure and the kinetic energy (proportional to the flow velocity squared) is a constant of the flow. As a result, a decrease in the pressure between two cross sections occurs simultaneously with an increase of the flow velocity.
The photo shows a simple experimental demonstration of Bernoulli's principle: the air flowing through the wider section of the tube has a higher (static) pressure than in the narrower section. For such a steady flow, the amount of fluid entering the pipe must equal the amount leaving the pipe, so the flow velocity in the narrower section is higher.
Other versions of Bernoulli's principle include also the differences in potential energy along a streamline, for instance resulting from the effect of gravity on differences in height. For compressible flows also the effects of thermodynamics on the internal energy are included. In such a form, the principle states that the sum of the pressure, kinetic energy, potential energy and internal energy is a constant along a streamline. Bernoulli's principle requires that viscous effects, heat transfer and entropy can be neglected.[1]
