Physics Help Forum Pressure and speed of fluid
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 May 19th 2008, 06:57 PM #1 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Pressure and speed of fluid For incompressible fluid in steady flow, when a pressure is applied, would there be a change in speed of fluid? When the cross section area is reduced, the speed rises, so would the pressure of fluid drops? What is the relationship between speed and pressure. I know that$\displaystyle P + pgy + pv^2/2$, could anyone explain in greater detail the relationship behind?
May 20th 2008, 01:51 PM   #2

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Bernoulli's Law says that
$\displaystyle P + pgy + \frac{1}{2}pv^2 = \text{constant}$

We also have
$\displaystyle A_1v_1 = \text{constant}$
(Continuity equation)

 Originally Posted by werehk For incompressible fluid in steady flow, when a pressure is applied, would there be a change in speed of fluid?
If we are applying a pressure then that pressure indicates a force from outside the system. The extra force per unit area on the fluid is certain to increase the speed of the flow.

 Originally Posted by werehk When the cross section area is reduced, the speed rises, so would the pressure of fluid drops?
From the continuity equation, when the cross sectional area drops, the speed must increase.

Thus from Bernoulli's equation the speed has increased meaning that the pressure must drop. (Assuming that the level of the fluid, y, remains unchanged.)

-Dan
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 Tags fluid, pressure, speed