Bernoulli Print

8/3/2019 Bernoulli Print

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UNDERSTANDING

BERNOULLI²S

PRINCIPLE



TRYTHIS

Blow under the tent.

Aim the air under the

tent by blowing

through a drinking

straw.

What happens????





Bernoulli·s principle statethat:

pressure of a moving fluiddecrease as the speed of the

fluid increase,

and

the pressure of a moving fluidincrease as the speed of the

fluid decrease.





How

aboutTHIS

1. Hold the strip of paper with

short edge below your bottom

lip.

2. Blow across the paper.

What happens????



Moving air creates a lowpressure region on top ofthe paper.

The still air below the paperhas higher pressure(atmospheric pressure) andso pushes the strip of paper

up.A resultant force exist dueto a difference in fluidpressure between twosurface.

The resultant force here isan upward force thatpushes the paper upward.

This is called lift.



T he fluid in incompressible (sameT he fluid in incompressible (same

density throughout) and flow easily.density throughout) and flow easily.

T he fluid flow is streamline or inT he fluid flow is streamline or in

layers, i.e. there are no eddies orlayers, i.e. there are no eddies orturbulenceturbulence..



A1A2

An incompressible fluid flowing through a

pipe which becomes increasingly narrower.

V1 = velocity at the

entry

A1 = cross sectional

area at the entry

V2 = velocity at the exit

A2 = cross sectional

area at the exit

Volume of fluid entering per second = A1V1

Volume of fluid leaving per second = A2V2

The fluid is

incompressible, so

A2V2 = A1V1

V2 = A1

V1 A2

Since A2 < A1, the flow

speed increase at the

narrow section of the

pipe.







APPLICATIONS OF

BERNOULLI²S

PRINCIPLE



Bunsen Burner

When the jet of gas flows out from the

nozzle with high velocity , the pressure

in the Bunsen burner becomes low.

A higher external atmospheric pressure

will be sucked into the air hole and bemixed with the gas .

The mixture of gas and air allows more

complete combustion of the gas.



A erofoil

Figure shows the streamlinesround a thin wing at an angle

of attack to the air stream.

It will be seen that the path of

air is longer over the upper

surface than the lower.

Therefore the speed is

greater on the upper surface,

and the pressure is lower at

the upper surface compare to

the lower surface.

The lift is produced by thedifference in pressure

between 2 surfaces.





PROBLEMS SOLVING

INVOLVING

BERNOULLI²S

PRINCIPLE



Given two situation.

1. A jet fighter with specially shaped wings

and body is seen taking off.

2. A racing car fitted with a specially spoiler

can move faster and is more stable.

a) From the situation given state two similar features to relate the airflow across the jet

fighter and the racing car. Relate these

features to Bernoulli¶s Principle

b) Explain how a racing car fitted with a

spoiler can maintain its stability whiletraveling at high speeds.



a) Both are shaped in such a way that the upper and lower

surfaces have different lengths.

Air flowing across the upper and the lower surfaces of an

aerofoil are at different speeds. The air pressure decreases

in the region where the speed of airflow increases. Thus a

lift is produced by a difference in air pressure between the

lower and upper surfaces of an aerofoil in the wings of the jet fighter whereas a down force is produced on the spoiler

of the racing car to provide better road holding.

b) Airflow is slower across the upper surface than the lower surface of

the spoiler. The air pressure is higher at the upper surface

than the lower surface of the spoiler. This produces aforce acting downwards on the car. The tyres of the car are

being pressed more firmly on the road by the force and

becomes more stable.



The roof of a house be lifted off by a

typhoon or strong winds due to its shape.

Explain why this can occur. Suggest two

modification on the design of the house to

prevent such a damage caused by the

winds.



The faster air flow above the roof creates a lower air pressure regionthere. Thus a lift is produced according to Bernoulli¶s principle. In

this way, the roof will be lifted off by the typhoon or strong winds.

So, to prevent such a damage, the following modifications can be

made:

The shape of the roof is redesigned to be flatter so that the

airflow above the roof is slower.

Openings are made below the roof to allow air to flow beneath

the roof, thus reducing the air pressure difference.







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Bernoulli Print