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TITLE : FORCE AND PRESSURE

NAME: DANIAL ADLI BIN AZMAN

CLASS : 402


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THE MEANING OF PRESSURE AND THE RELATIONSHIP

Pressure is the force which acts normal per unit area of contact.

P=FA

where P= pressure [Pa]

F= force [N]

A = area [m2]


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PHENOEMENA OF PRESSURE IN DAILY LIFE

1)

A sharp knife has a very small surface area on its cutting edge so that high pressure

can be exerted to cut the meat.

2)

The pressure of the base of high -heeled shoe is high due to the small surface area

of the base of the shoe.

3)

The pressure of the base of a shoe is low as the surface area of the base o f the shoeis large.


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4)The tyres of a tractor have a large surface area of contact with the ground and

therefore the smaller pressure on the ground prevents the tractor from sinking into

the ground.


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PRESSURE IN LIQUID

Pressure in liquids are not dependent on the size or shape of the container; only on

its depth.

P=hg

where P= pressure [Pa]

h = height of liquid [m]

= density of liquid [kg m-3]

g= gravitational acceleration [m s-2]


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PASCAL PRINCIPLE AND APPLICATION

Pascals Principle dictates that pressure which is exerted onto the surface of a fluid

in a

closed container will be transferred uniformly throughout the entire fluid.

F1=F2 A1 A2

All hydraulic systems are built based on Pascals Principle.

1) Hydraulic jack

When the lever is pushed downwards, valve A closes while valve B opens.

Pressure is transferred to the larger cylinder and creates a large force to lift the car.


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When the lever is pulled upwards, valve B closes while valveA opens. The

hydraulic

oil flows out from the tank to fill the space in the small cylinder.

As every movement downwards by the lever creates a small movement upwards

for

the large piston, the lever needs to be pushed and pulled repeate dly before the car

can

be raised to a certain height required.

The car can be lowered down by opening the release valve so that the hydraulic oil

can flow back into the tank.

2) Hydraulic brake

When the driver steps on the brake pedal, the piston in the main cylinder transfers

pressure through the hydraulic oil in the cylinders.

Pressure is transferred uniformly through the hydraulic oil.

The pistons in the slave cylinders are larger, therefore a large amount of force is

transferred to the brake pads.

The brake pads transfer the large amount of force onto the disc so that the rotation

of

the tire is slowed down.


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3) Hydraulic pump

A hydraulic machine uses a hydraulic pump to transfer hydraulic liquid from one

vessel into a large cylinder to create a movement.

The above diagram shows a hydraulic pump used to move the arm of a crane.


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BERNOULLIS PRINCIPLE AND THE PHENOEMENA IN DAILY LIFE

Bernoullis principle dictates that when the velocity of a flowing fluid increases, the

pressure at that point decreases.

Uniform tube:

(a) When a uniform tube with one end stopped is filled with water, the levels in all

three vertical tubes are the same.

Water pressure at A = Water pressure at B= Water pressure at C

(b) When the stopper is removed, it is found that the water levels are decreasing

from P

to Q to R.

Water pressure at A > Water pressure at B> Water pressure at C

This is because water flows from high pressure to low pressure.

Venturi tube:

(a) When a Venturi tube with one end sto pped is filled with water, the levels in all

three vertical tubes are the same.

Water pressure at X = Water pressure atY = Water pressure at Z

(b) When the stopper is removed, it is found that the water levels are the lowest at Y

and the highest atX.

Water pressure at X > Water pressure at Z > Water pressure atY


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The tube cross-section at Yis the smallest, therefore water travels at the fastest

velocityat tube Y. Therefore, the pressure at Yis the lowest.

The water velocity in tubeXand Zare the same because they have the same

crosssection area. However, the pressure gradient still decreases from D to E to F,

which is why the water level at Zis lower than atX.

1) Aerofoil

As the aerofoil shape cuts through the air, the air is

forced to travel at a higher speed on top of the

aerofoil compared to below the aerofoil.

The high velocity area causes the air to have low

pressure.

Therefore, the higher pressure area pressures

against the aerofoil towards the lower p ressure area

causing a lifting force.


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2) Carburetor

Carburetor mixes petrol and air for burning

in the engine cylinder.

When air flows through the narrower part of

the tube, the velocity increases thus the

pressure decreases. An area with low

pressure is formed at X.

The atmospheric pressure, which is greater,

pushes the petrol out from the jet.

Petrol and air are mixed to create a spray

3) Bunsen Burner

Gas flows out through the narrow jet at a very high ve locity.

A low-pressured area is formed at X.

The air outside at atmospheric pressure flows in and mixes

with gas to light it.


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Oxygen supply which is enough from the air will ensure a

complete burning to produce a hotter flame and less

luminous.


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ARCHIMEDES PRINCIPLE AND THE APLICATIONS

Archimedes principledictates that when an object is partially or fully immersed in a

fluid, the object undergoes a buoyant forcewhich is equal to the weight of the fluid

displaced.

Buoyant force = Weight of fluid displaced= Vg

where V= volume of fluid displaced [m3]

= density of fluid [kg m-3]

g= gravitational acceleration [m s -2]

If the object is floating stationary:

Weight of object = Weight of fluid displaced

Submarine

The buoyant force acting on the submarine is always the same because the weightof fluid

displaced is always the same.

When water is pumped into the ballast

tank, the weight of the submarine increases.


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When the weight of the submarine is

greater than the buoyant force, the

submarine sinks.

When water is pumped out of the ballast

tank and replaced with air, the weight of

the submarine decreases. When the weight

of the submarine is less than the buoyant

force, the submarine floats.

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