3.6 bernuolli's principle

8/3/2019 3.6 Bernuolli's Principle

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3.6BERNOULLIS

PRINCIPLE


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Bernoullis Principle

Bernoullis principle states that when the velocity ofa fluid is high, the pressure is low, and when the

velocity is low, the pressure is high.


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When water is not flowing, the water levels P, Q andR at the vertical tubes are the same.- when water is not flowing, pressure at A, B and Care the same.

When water is flowing at a steady rate, water levelsat the vertical tubes are decreasing.- when water is flowing at a steady rate, it flows fromhigher pressure to lower pressure.

Water not flowing

Water flow at a steadyrate


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When water is not flowing, the water levels P, Q and R at thevertical tubes are the same levels.

When water is flowing at a steady rate, water level at P1 is thehighest and its level at Q2 is the lowest.

- when the water is flows into a narrower section of a tube, itsspeed increases, hence, at B, the water flows at a highervelocity and its pressure is the lowest.

Water not flowing

Water flow at a steadyrate


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Application of Bernoullis Principle

Aerofoil

The Bernoullis effect can be seen in lifting of an aeroplane.

The wing of an aeroplane has the shape of an aerofoil.

When the plane is moving horizontally, air flows over theaerofoil. The wing is curved at the top and relatively flatter atthe bottom because of the shape and orientation of the wingare slightly tilted.

The streamlines are closer together at the top, hence, the air

speed is greater above the wing than below it.

The difference in the speed causes lower air pressure abovethe wing than below it. A net upward force or lift is resulted.


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Bunsen Burner

When the compressed gas flows through the jet at high speed,the area around the jet has a low pressure. Atmosphericpressure will force the surrounding air into the burner. Themixture of the gas and air allows a complete combustion.


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Atomiser

When a rubber bulb of the atomiser ispressed, air is blown out of it at high speed.Its pressure becomes lower than thesurrounding atmospheric pressure. Perfumeis pushed out by the atmosperic pressure andis blown out of the tube in fine droplets.

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Carburetor

The barrel of the carburetor in a car has a narrow construction.The flowing air speeds up as it passes through this

construction, and so the pressure is lower. The higheratmospheric pressure forces the petrol into the construction.The mixture of petrol and air is sent for burning in thecombustion chamber of the engine.
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3.6 bernuolli's principle

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