jgn tiru bulat2
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Transcript of jgn tiru bulat2
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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.