In a steady flow of a fluid, the pressure of the fluid decreases when the velocity of the fluid increases.

Fluid consist of liquid or gas

Demo: Blow It UpHold a sheet of paper in front of your mouth

and blow; the paper will rise.

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Observation Explanation

As air is blown across the top of a piece of paper, air flows at high speed and this creates a region of low pressure across the top of the paper. The still air beneath the paper is at a higher pressure and a net upwards force lifts the paper.

As air is blown vigorously between two sheets of paper held vertically, air flows at high speed and this creates a region of low pressure between the two sheets of papers. The outside air the paper which is at a higher pressure presses the two sheets of papers together.

Evidence of Bernoulli’s Principle in our daily lives

Demo: Blow It OffBend cardboard into a U-shape. Place on table,

legs down, and try to blow it off.

Side view

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Fast moving air in the channel between the card and the table creates a low pressure region, pressing the card downward.

Demo: Keep It UpObjects in a moving steam of fluid are pulled to the center of the

stream because pressure is lower inside the stream than outside.

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Observation Explanation

As air is blown out from the pipe, air flows at high speed and this creates a region of low pressure across the top of the pipe. The still air around the ball is at a higher pressure and pushes on the ball and causes it to stay in the air.

As air is blown vigorously between two ping pong balls, air flows at high speed and this creates a region of low pressure between the two balls. The outside air the balls which is at a higher pressure presses the two balls together.

Demo: Blow the Funnel

Blow hard through a funnel with a ping pong ball in the funnel’s bowl.

Instead of being blown away, the ball is held tightly in the bowl.

PingPongBall

BLOW

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Observation Explanation

As air is blown into the funnel, air flows at high speed at the narrow passage and this creates a region of low pressure at X. The still air beneath the paper is at a higher pressure and a net upwards force lifts the ball.X

Observation Explanation

Water flows from a region of high pressure to a region of low pressure.

As fluid flows pressure decreases.

Observation Explanation

Velocity of fluid at a narrow passage is faster than at a broad passage.

As the velocity increases, the pressure decreases (Bernoulli’s Principle)

Observation Explanation

Liquid flow As the tube narrows, the fluid flows more quickly and correspondingly, pressure in the narrow section decrease, therefore the water level is low.

Observation Explanation

Air flow As the tube narrows, the fluid flows more quickly and correspondingly, pressure in the narrow section decrease, therefore the water level is low.

Observation Explanation

Air flow

Observe the liquid level and the pressure difference in the 3 tubes.

Venturi Tube

As air is blown through a tube as shown in the figure on the left, the region in the narrow section has a lower pressure. The external atmospheric pressure pushes the water to its highest level in this section.Water level at C is lower than at A because as air flows, pressure decreases.

Airplane WingPressure difference created by Bernoulli effect

creates upward lift.

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Wing

LIFT FORCE

A spinning ball curvesVelocity of air and velocity of ball = opposite= reduced velocity of air flow = high pressure

Velocity of air and velocity of ball = same= increased velocity of air flow = low pressure

Observation Explanation

Insecticide sprayer /Perfume sprayer

When the plunger is pushed in, the air flows at a high velocity through a nozzle. The flow of air at high velocity creates a region of low pressure just above the metal tube. The higher pressure acts on the surface of the liquid insecticide causing it to rise up the metal tube. The insecticide leaves the top of the metal tube through the nozzle as a fine spray.

Application of Bernoulli’s Principle in our daily lives

Observation Explanation

Bunsen burnerWhen the burner is connected to a gas supply, the gas flows at high velocity through a narrow passage in the narrow nozzle, creating a region of low pressure. The outside air, which is at atmospheric pressure is drawn in and mixes with the gas. The mixture of gas and air enables the gas to burn completely to produce a clean, hot, and smokeless flame.

Observation Explanation

Water pumpA jet of water flows at high speed at the nozzle. This creates low pressure at the region. Air from the vessel is of high pressure and therefore is drawn out from the vessel and into the water pump.

Observation Explanation

Carburetor The air flows past a choke valve, which controls the quantity of air, into a narrow a section of the carburetor where the air velocity increases.

Aerodynamic shape of a car :i.Creates an upward force that lifts the car up.ii.Reduces air friction (less drag)

Theses enable the car to move forward faster.

Observation Explanation

As the wing of a car or a bird moves forward, the air flows at higher speed on top of the wing and this creates a region of low pressure on top of the wing. The slower air flow beneath the wing has a higher pressure. The difference in pressure produces a net force that pushes the wing up.

The shape of the wing is called Aerodynamic.

Phenomena of Bernoulli’s Principle

Blow the RoofIf wind blows hard enough

the low pressure above can create a large enough force to lift the roof off.

New Orlean’s Superdome after hurricane Katrina

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