F4Ch3student

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CHAPTER 3

FORCES AND PRESSURE

3.1 Understanding pressure ( / 8 x 100 % =

% )

A student is able to:

Define pressure and state thatA

FP =

Describe applications of pressure

Solve problems involving pressure

1. What is meant by pressure?

.......................................................................................................................................

.

2. Choose ( ) the examples that apply the concept of pressure?

( ) Toothpaste ( ) Nail

( ) Larger and wider seat belt ( ) Knife

( ) Ship ( ) Aerofoil

3.

A girl is going to take a walk on a soggy field. There are two types of shoes as in

diagram 3.

Which type of shoes should she wear?

.......................................................................................................................................

.

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4. Diagram shows a cuboid of 2 kg on a table.

Calculate the pressure exerted on the table by the cuboid. Tick () the correctanswer.

Diagram 4

( ) 0.8 N m-2

( ) 50 N m-2

( ) 200 N m-2

( ) 500 N m-2

5. Diagram 5 shows different situations of a cuboid of 5 kg on a table.

Circle the diagram in which the cuboid exerts the least pressure on the table.

Diagram 5

2

0.4 m

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3.2 Understanding pressure in liquids ( / 8 x 100 % = %

)


relate depth to pressure in a liquid

relate density to pressure in a liquid

explain pressure in a liquid and state that P = h g

describe applications of pressure in liquids.

1. What is the relationship between depth of liquid and pressure?

............................................................................................................................

2. What is the relationship between density of liquid and pressure?

..............................................................................................................................

3.

Diagram 3Diagram 3 shows a container of oil.

Underline the correct answer

Point ( X , Y ) has the highest pressure?

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4. The relationship of Pressure in liquid is, P =hg

What is represented by h, and g respectively?

h =..............................

= .............................

g =.............................

5. State one application of pressure in liquid.

...............................................................................................................................

6.

Diagram 6

Diagram 6 shows a glass full of alcohol.

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What is the pressure at P? Tick () the correct answer.

[ Density of alcohol = 800 kg m-3 ]

( ) 1600 Pa

( ) 16 000 Pa

( ) 160 000 Pa

( ) 1 600 000 Pa

3.3 Understanding gas pressure and atmospheric pressure

( / 15 x 100 % = % )


explain gas pressure

explain atmospheric pressure

describe applications of atmospheric pressure

1. A student wrote several statements to explain the gas pressure.

However they were in the wrong order.

Rearrange the statements in sequence to explain the gas pressure.

[Write numbers 1, 2, 3 or 4 in the sequence column]

Sequence Statements

Collisions of gas particles in the container occur very frequently.

The gas is made up of gas particles.

The collisions of gas particles on the wall of container give rise to gas

pressure

The gas particles move randomly with high speed.

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2.

Diagram 2

Diagram 2 shows a manometer connected to a gas tank.

Determine the gas pressure shown.[ Atmospheric pressure = 76 cm Hg]

3.

Diagram 3

Diagram 3 shows a manometer.

What will happen to the mercury column Y if X is connected to a high pressure of gas

tank?

..

4. Underline the correct answer.

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(a) The ( weight , mass ) of air on the earths surface caused the atmospheric

pressure.

(b) A mountain terrain has a ( higher , lower ) atmospheric pressure than atthe sea-side because the air at the mountain terrain is ( thicker , thinner ).

5. It is found that a Fortin barometer reads 74 cm Hg at a highland

whereas the reading is 76 cm Hg at the sea side.

Based on the statement, tick ()

i. a correct inferenceii. a correct hypothesis

i ( ) The atmospheric pressure is influenced by the altitude

( ) The atmospheric pressure is influenced by the type of barometer

ii. ( ) The higher the altitude from sea level the lower the atmospheric pressure

( ) The lower the altitude from sea level the lower the atmospheric pressure

6. Fortin barometer X reads 74 cm whereas Fortin barometer Y reads 76 cmHg.

Which of the following statements correctly explain the difference of atmospheric

pressure in the terms of altitude?

Tick () at the correct statements.

The Fortin barometer X measured the atmospheric pressure at lower altitude.

The Fortin barometer X measured the atmospheric pressure at higher altitude.

The Fortin barometer Y measured the atmospheric pressure at lower altitude.

The Fortin barometer Y measured the atmospheric pressure at higher altitude.

8. List two applications of atmospheric pressure.

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i . ...............................................................................................................................

ii. ...............................................................................................................................

3.4 Appling Pascals Principle ( / 10 x 100 % =

% )


state Pascals principle.

Explain hydraulic system

Describe applications of Pascals principle.

Solve problems involving Pascals principle.

Instruction :Answerallquestions in this section.

1. Pascals Principle states that

...............................................................

.

..

2. Some examples of the application of the Pascals Principle are

.. ,

.......................

3. Diagram 3 shows a application of Pascals Principle.

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Diagram 3

State the relationship between F1, F2, A1 and A2.

4. The diagram 4 show one application where pressure is transmitted

equally through an oil. Name of the system : ..

Diagram 4

5. Diagram 5 shows toothpaste being squeezed out from the tube. The principle

that explains the situation below is

Diagram 5

6. Diagram 6 shows a :..

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Diagram 6

7. Diagram 7 shows a simple hydraulic system. A1 and A2 are cross

section area of the piston. A1 = 5 cm2 and A2 = 10 cm2.

Diagram 7

(a). What is the minimum force F1 which can lift a load of 100 kg ?

(b). What will happen to the hydraulic jack if the force F1 is less than the value

found in 7(a)?

(c). Give one reason for your answer

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3.5 Applying Archimedes Principle ( / 3 0 x 100 % = % )


Explain buoyant force

Relate buoyant force to the weight of the liquid displaced

State Archimedes principle.

Describe applications of Archimedes principle

Solve problems involving Archimedes principle

Instruction :Answerallquestion in this section.

1. Buoyant force is the

.

.

2. Archimedes' Principle states that

.........................................

.

.

.

3. The examples of application of Archimedes' Principle are:

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.., ... , .

.

4. What is the relationship between the buoyant force and the weight of

water displaced ?

5. Diagram 5 shows a spring balance supporting a metal block K in three

situations.

Diagram 5

(a)Compare the readings of the spring balance in Diagram 5A and Diagram 5B.

(b) Name three forces that act on K when it is partially or totally immersed in

water.

.., .,

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(c) State and explain the relationship between the forces in (b).

(d) Name the principle involved in question (c).

(e). (i). What will happen to the spring balance in diagram 5C if the water is

replaced with salt solution?

(ii) Give one reason for your answer.

....

.

6. A submarine can sail on the sea surface and under the sea. Explain how

a submarine on the surface submerges.

a) The submarine has a ____________.

b) Water is _________ in the ballast tank.

d) The submarine sinks into the water when its ___________ is more than the

____________ of the water and its weight is equal/more than the _______.

7. A fisherman finds that his boat is at different levels in the sea and in the river,

although the boat carries the same load. Diagram A and B below illustrate the

situations of the boat in the sea and in the river.

Diagram 7

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Compare the levels of the boats in diagram 7 and the volumes of water displaced by

the boat. Relating the mass of the boat with its load, the volume of water displaced

and the density of the water, deduce a relevant physics concept.

a) The boat _________ more in the river than in the sea.

b) Sea water is ___________ than river water.

c) The _________ of the boat and its load is the same when it is in the

sea and in the river.

d) The boat floats because it is being balanced up by the _____________.

e) The upthrust is equal to the weight of _________________.

f) More water will be ___________ when the density is lower.

The boat _________ more when the density is lower.

8. Diagram A and B illustrate the working principle of a hydrometer. The depth to

which the test tube sinks depends on its surrounding liquid.

Diagram 8Explain how you would design a hydrometer that can determine a wide range

of densities of liquid, using the idea of the working principle of hydrometer in diagram

8A and diagram 8B. Draw a diagram that shows the design of your hydrometer and

in your explanation. Emphasized the following aspects:

- the stability of the hydrometer,

- the sensitivity of the hydrometer,

- the ability to measure a wide range of densities of liquids,

- the calibration of the hydrometer.

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a) Draw a correct design of the hydrometer.

b) Put ___________ balls in the glass bulb, to ensure the hydrometer is upright.

c) Use a _________ stem, to have a bigger interval of the scale.

d) Use a suitable big bulb and a ________ stem. So that the hydrometer

does not sink fully in low density liquid.

e) __________ the hydrometer in a paraffin oil / alcohol. The scale and the level

of liquid at the stem will show the density of paraffin oil / alcohol. This is to

make calibration for liquid of low density.

f) __________ the hydrometer into a carbon tetrachloride solution. This is the

calibration for liquid of high density. Make the scale at the stem using the

upper and the lower level of density.

Learning Objective

3.6 Understanding Bernoullis principle. ( / 30 x 100 % = % )

Learning Outcomes

A student is able to: State Bernoullis principle

Explain that resultant force exists due to a difference in fluid pressure

Describe applications of Bernoullis principle

Solve problems involving Bernoullis principle

Instruction :Answerallquestions in this section.

1. Bernoulli's Principle states that

..

2. The examples of application of the Bernoulli's Principle are:

i ..,ii ....,iii.

..,

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iv.,v.

.

3. Diagram below shows a piece of paper hanging from a retort stand. When air

flows from the nozzle of an air pump, the paper changes its position as shown

in Diagram B.

Diagram 3

(a) Compare the position of the paper in Diagram 3A and Diagram 3B.

.

(b) F is a force that causes the paper to change its position. In box X, on

Diagram B, indicate and label the direction of F that acts on the paper.

(c) Explain how F is produced.

i.

ii.

(d) (i) Compared to the position of the paper in Diagram B, how does the

position of paper change when the air flows faster ?.

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.

(ii). Give a reason for your answer in (d)(i).

.

(e) Name the principle that causes the observation in Diagram B.

.

4. Diagram A below shows the situation of a sheet of paper before and when air is

blown. Diagram B shows the situation of canopy before the lorry moves and

when the lorry moves at high speed.

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Diagram 4

(a) Based on Diagram 4A and Diagram 4B :

(i) State two similarities for the situations in Diagram 4A andDiagram 4B.

i.

ii

(ii) Compare the air pressure above and below the paper when air

is blown.

(iii) Relate the speed of the air to the pressure of the air.

(b) Name the principle involved in question (a)(iii).

5. Diagram 5 shows an instrument used to measure the speed of air.

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Diagram 5

In Diagram 5A shown the level of coloured water in the U-tube is the samebefore air flows.

(a) Compare the speeds of air at P and at Q after air flows at diagram B.

(b) Mark the water level in the U-tube in Diagram B when air flows.

6. Diagram 6 shows a cross-section of a wing of a moving aero plane.

The wing of the aeroplane experiences a lift force.

Diagram 6

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(a) Name the shape of the cross-section in Diagram 6.

..

(b) Explain why the lift force acts on the wing of the aeroplane.i

ii

iii

7. Diagram 7 shows a model of an aeroplane.

Diagram 7

You are required to give some suggestions to design a aero plane which can

travel faster and more stable.

Using the knowledge on motion, forces and the properties of materials, explainthe suggestion based on the following aspects:

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- the surface of the plane

- the shape of the plane

- material used for the plane

- position of the wing

- the size of the wing

a) __________. To reduce air friction between air plane and air.

b) _____________ shape. To reduce air friction also.

c) ________________ material. To reduce the weight and easy to fly.

d) The wings are positioned higher up on the body so that the aeroplane is

_________________ .

e) ___________. To increase the uplift (force)..

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