APPLICATION OF PRESSURE IN EVERYDAY IN LIFE

CHAPTER 3 : FORCES AND PRESSURE

3.1 UNDERSTANDING PRESSURE

1. DEFINITION : _________________________________________________

2. FORMULA :

3. SI UNIT :

FACTORS THAT AFFECT THE PRESSURE ACTING ON A

SURFACE

EXAMPLE 3.1

A block of metal of dimensions 0.5 m x 0.6 m x 1.0 m has a mass of 300 kg. Calculate the maximum pressure acting on the

EXAMPLE 3.2

The diagram below shows a wooden block of dimension 8 cm x 10 cm x 12 cm. Its weight is 120 N. On which side should the

Exercise 1

1. A table of mass 50 kg has four legs is placed on a floor. Each leg has a cross setional are of 25 cm2. Find the pressure exerted on the floor ( g = 10 ms-2 ) Ans: 50 kPa

2. Wind blows normally on a wall at a pressure of 200 kPa. If then wall has an area of 5 m2, what is the force acting on the wall? Ans: 1000 kN

3. A cylinder has a mass of 12 kg and a cross-sectional area of 200 cm2 . what is the pressure acting at its base ? Ans: 6 kPa

3.2 UNDERSTANDING PRESSURE IN LIQUIDS

Definition pressure in liquid : ______________________________________

EXAMPLE 3.1

A block of metal of dimensions 0.5 m x 0.6 m x 1.0 m has a mass of 300 kg. Calculate the maximum pressure acting on the

EXAMPLE 3.2

The diagram below shows a wooden block of dimension 8 cm x 10 cm x 12 cm. Its weight is 120 N. On which side should the

EXAMPLE 3.3

1. An air bubble is at a depth of 5 m below the surface of a lake. What is the pressure of water on the bubble if the density of the water is 1000 kg m-3 ? Ans: 50000 Pa

2. The figure shows a high tin with a length of 100 cm is filled to the full with water.

If the pressure caused by the water at point P is 8000 Pa, what is the value of L ?

( Density of water = 1000 kg m-3 ) Ans: 20 cm

3. The density of water is 1000 kg m-3

Find the density of liquid X in kg m-3?

Exercise 2

1. Mercury has density of 13600 kg m-3. If the pressure of mercury is 650 kPa, what is the depth of its surface ?

2. Water has a density equal to 1 g cm-3. What is its pressure at depth of 12 m from surface.

3. A ballon is situated at 10 m below sea level, what is the total pressure experianced by the ballon ? [ the density of sea water is 1100 kg m-3 ]

Total pressure , P = Atmospheric pressure + Liquid pressure

3.3 UNDERSTANDING GAS PRESSURE AND ATMOSPHERIC PRESSURE

Application of pressure in

liquids

Intravenous infusin

Construction of dam

Location of water tank

Construction of submarine

`

Gas Pressure

1. The gas pressure in container is caused by the ___________ of gas molecules with __________ of the container.

2. Gas pressure can be measure by using two types of instrument known as;a) ___________ gauge ( consist of semi-circular or C – shaped copper tube )b) ______________ ( consist of a U – tube abaut 1 m in height )

Atmospheric Pressure

1. The atmospheric pressure is caused by ____________ exerted by the air, as the weight of the atmosphere on the Earth’s surface.

2. 1 atmosphere = _________mm Hg = __________ m water = _____________ Pa

Altitude and magnitude of Atmospheric Pressure

The greater the __________ from the sea level , the ___________ will the atmospheric pressure.

Instrument for Measuring Atmospheric Pressure

Barometer is an instrument to measure atmospheric pressure. There are 2 types of barometer;

a) _______________________b) ________________________

EXAMPLE 3.4

1. The atmospheric pressure is 760 mm Hg. What is the value of the atmospheric pressure in Pascal? [ Density of mercury , ῤ (Hg) = 13 600 kg m-3 ]

Atmospheric pressure , Patm = h p g = _________

2. Figure show apparatus set up which is used to measure atmospheric pressure.

Calculate the pessure at point Q in Pa unit. [Mercury density = 1.36 x 104 kgm-3]

3.

Figure show manometer connected to gas tank whose valve is then turned on. What is the pressure of the gas , in unit N m-2 , in tank.

[ Density of water = 1 000 kg m-3 ]

Exercise 3

1. If the atmospheric pressure is 76 cm Hg, what is thepressure of the trapped air P ?

2. What is the pressure of the gas trapped inside the J-tube, in Pa unit?

3. Diagram below shows a set up of apparatus for measuring atmopheric pressure.

Determine the atmospheric pressure in i) cm Hg ii) Pa unit.

3.4 APPLYING PASCAL’S PRINCIPLE

1. Definition : Pascal’s Principle state that the pressure exerted on an __________ fluid is transmitted _________________to every part of the fluid.

2. Draw the direction of water:

HYDRAULIC SYSTEM.

1. In the hydraulic system is used to produce a ______ force out of a small one. The hydraulic system also known as a force ___________ .

2. The application of Pascal’s principle can be found in _____________________ & ________________________

EXAMPLE 3.5

The figure shows a basic hydraulic system has small and large pistons with cross-sectional area of 0.005 m2 and 0.1 m2 respectively. A force of 20 N is applied to the small piston.

Exercise 4

1.

Determine;

i) the pressure transmitted in the hydraulic fluid.

ii) the mass of the load

iii) if the small piston is pushed down at a depth of 0.04 m, what is the distance moved by the large piston?

2. Figure below shows a hydraulic jack. Piston A and piston B have cross-sectional area 5 cm2 and 100 cm2 respectively. If mass of 3 kg is placed on a piston A, what is the maximum weight that can be lifted by piston B?

3.

3.5 ARCHIMEDES’ PRINCIPLE

1. Definition : Archimedes’ Principle said that when an object is _________ or __________ immersed in a fluid, the uptrust or ___________ on it is equal to the ____________ of fluid displaced.

2. Buoyant force makes things seem to be __________

3. Bouyant force is the __________ force resulting from an object being wholly or partially immersed in a fluid.

4. The weight of an object in the air is its _______ weight.

5. The weight measured when the objeect is immersed in a fluid is its __________ weight.

6. The apparent weight loss of the object is due to ____________

7. When in water, the object experiances two forces ;

1. The ______________ which acts downwards2. The ______________ which acts upwards.

8. The buoyant force is equal to the apparent loss in weight.

Buoyant force = actual weight – apparent weight

= 25 – 15 = 10 N

9. The object displaces a volume of water. The ___________ the volume of the object immersed, the _________ the volume of liquid displaced.

Volume of liquid displaced = volume of the submerged object

Buoyant force = weight object in air – weight in water

Buoyant force = weight of fluid displaced

Buoyant force = pVg

EXAMPLE 3.6 EXAMPLE 3.7

An object of density 40 g cm-3 and mass 500 g is immersed in a liquid of density 2 g cm-3. Calculate ;

a) the volume of liquid displaced

b) the mass of liquid displaced

c) the buoyant force experianced by the object ( g = 10 ms-1)

APPLICATIONS OF ARCHIMEDES ‘ PRINCIPLE

3.6 BERNOULLI’S PRINCIPLE

1. Bernoulli’s principle states that ................................................................................................................................................................................................................................................................................................

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APPLICATIONS OF BERNOULLI’S PRINCIPLE