Class 6 Times Science

Based on New Curriculum

Approved by Curriculum Development Centre (CDC) Sanothimi, Bhaktapur,
Nepal as a reference material for schools.

Times’ Crucial

SCIENCE
and ENVIRONMENT

6Grade

Authors: Editor:
Dr. Krishna Prasad Sigdel Kamal Prasad Sapkota
Rajan Kumar Shrestha M. Sc., M. A., B. Ed.

Published by: Times International Publication Pvt. Ltd.
Authors:
Dr. Krishna Prasad Sigdel
Series Editor: Rajan Kumar Shrestha
Edition:
Kamal Prasad Sapkota
Layout:
First: 2070 B.S.
Revised: 2074 B.S.
Reprint: 2075 B.S.
Reprint: 2077 B.S.
Surendra Nakarmi

© Copyright: Publisher

Printed in Nepal

Preface

Human life is always in progress. Newer technologies and equipments have been
developed or discovered in every second. Lengthy and time consuming work of
past are now done within a few moments. People can travel far off distances within
short time. Several fatal diseases have been eradicated. These achievements, what
we are enjoying today, are the results of advancement in science and technology.
Hence, science has become an integral part of our education system.

Times’ Crucial Science & Environment is a series of text books for the school
level students of grades LKG to class ten. The series has been prepared for the
young learners emphasizing on student-centred teaching techniques, learning
circle based activities, practicable activities, scientic approaches and innovative
learning techniques. The text of each lesson is preceded by a warm up activity
that encourages students to take part actively in the learning process. The series
includes the teaching techniques and methods for the teachers under the title
’Note to the Teacher’. It is based on the latest syllabus prescribed by CDC
Government of Nepal. Hence, this series acts as the foundation of science for
the curious and inquisitive young minds.

Each book of this series covers the syllabus of Science & Environment. The rst
part contains chapters of Science and the second part, chapters of Environment
Science. All the chapters of Science and Environment are provided with a wide
variety of exercises which encourage the students in learning and sharpening
their mind. A project work is asked at the end of each lesson so that student
can apply their knowledge to solve the problems of their day-to-day life. In
the beginning of each lesson, thought provoking questions are given under the
heading “Mind Openers”. This activity will compel students to use their brain.

We feel delighted to extend our sincere gratitude to Mr. Kamal Prasad Sapkota
for his painstaking contribution in editing the book and making it more simple
and crucial. We are equally thankful to the publishers Mr. Sunil Subedi without
whom this series would not have been possible in the present form. We are also
thankful to Mr. Surendra Nakarmi for providing this smart form to the book.

Constructive suggestions and recommendations from teachers, students and well
wishers for the further improvement of the books are welcome.

- Authors

Contents Page No.

SN Contents 1 - 15
Physics 16 - 27
28 - 38
1 Measurement 39 - 52
2 Force and Motion 53 - 61
3 Machine 62 - 69
4 Heat 70 - 80
5 Light 81 - 88
6 Sound
7 Magnet 89 - 101
8 Electricity 102- 117
118 - 125
Chemistry 126 - 137
9 Matter 138 - 143
10 Mixture
11 Air 144 - 156
12 Metal and Non-metal 157 - 169
13 Some Useful Chemicals 170 - 177
178 - 191
Biology
14 Types of Plants 192 - 200
15 Types of Animals 201 - 209
16 Cell and Tissue 210 - 220
17 Life Process
221 - 234
Geology and Astronomy 235 - 251
18 The Earth 252 - 259
19 Weather and Climate
20 The Earth and Space 260
261
Environment Science 262 - 266
21 Environment and its Balance 267 - 268
22 Environmental Degradation and its Conservation
23 Environment and Sustainable Development

Specication Grid
Terminal Break-down of the Courses
Model Test Papers
Practical Examination

Chapter

1 MEASUREMENT
Estimated periods:7

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü explain the need of measurement and use the proper units of

measurement;
Ü introduce local and ancient systems of measurement;
Ü introduce FPS, CGS, and MKS system of measurement;
Ü use different units to measure length, mass and time;
Ü recognize and use simple instruments of measurements.

MIND OPENERS
Ü What do you do while buying goods in shop?
Ü What gives you information about ‘time’?
Ü How do you know the distance between any two points?
Ü What things do you use to measure length of objects?
Ü Why is measurement necessary?

Introduction

When you go to the shop to buy rice, sugar, pulses, kerosene or cooking
oil, the shopkeeper measures the amount or quantity of these things
as per your need. The cost of these things depends on their quantity
and the quantity is found out only after measurement. We measure
several things in our daily life. We use different instruments to
measure different things. For example, we measure the temperature
of our body with the thermometer, we measure the mass of the fruits
with a beam balance, we measure time with a watch or clock, etc.

We can measure most of the quantities whatever we talk about. The
quantities which can be measured are called physical quantities.

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For example, time, length, mass, temperature, etc are physical
quantities. But the feelings such as anger, love, affection, happiness,
sadness, etc cannot be measured. Such quantities are called
non-physical quantities.

Activity 1.1

Bring a metre tape, scale, watch or clock, thermometer, beam balance,
etc to your class and measure different quantities such as length and
breadth of your science book, time taken by your friend to count all
pages of your science book, temperature of your body, mass of a
brick, etc.

Measuring tape Beam balance Wall clock

In the above activities, we compare the unknown amount or
quantity with a known quantity. This process of comparison is called
measurement. Thus, the process of comparing an unknown physical
quantity with known standard quantity is called measurement.

Importance of measurement

Measurement is essential in our daily life. In fact, almost all of our
daily activities involve measurement directly or indirectly. The
importance of measurement can be summarized as follows:

1. We need measurement while buying, selling or exchanging
the goods.

2. We need measurement of time while working.

3. We need measurement while preparing our meals.
4. We need measurement while sewing the clothes.

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5. Measurement plays crucial role in scientic experiment,
discoveries, invention, etc .

Traditional systems of measurement

Different kinds of measurement are in existence since the ancient
time. In the past, people had their own ways to measure physical
quantities. For example, footstep, arm, hand span, ngers, etc were
used to measure length. Similarly, the position of the sun, moon and
stars in the sky were used to measure time and Mano, Pathi, Dalo,
etc were used to measure the amount of food grains. The Mano, Pathi
and Dalo are still in use in the remote areas of our country.

Mano Pathi Dalo

Activity 1.2

Divide the class into the groups of ve students each. Then measure
the length of your table (Use separate table for each group) with
arms, hand and nger. Also measure the distance between two walls
of your classrooms using footsteps.

Did all ve members of a group nd same length of the table or the
room ?

The answer is ‘no’. Why is it so ?

The length of arm, hand span, footstep, etc differs from person
to person. Similarly, Mano, Pathi and Dalo can have different
capacities according to the skill of constructors. Hence, such systems
of measurement are not accurate. Such measurements differ
from person to person and place to place. If we use this system of

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measurement, the same quantity can have different measurements at
different places. Therefore, the traditional systems of measurement
are being replaced by scientic system in present days.

Different systems of measurement

Different systems of units are used to measure the physical quantities.
Some commonly used systems of units are described below:

CGS system

The system of units in which length is measured in centimetre, mass
is measured in gram and time is measured in second is called CGS
system. It is a French system of measurement.

Length Mass Time
Centimetre Gram Second

C G S

FPS system

The system of units in which length is measured in foot, mass is

measured in pound and time is measured in second is called FPS
system. It is the British system of measurement.

Length Mass Time
Foot Pound Second
F
P S

MKS system

The system of units in which length is measured in metre, mass is
measured in kilogram and time is measured in second is called MKS
system.

Length Mass Time
Metre Kilogram Second

M K S

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SI system

Only length, mass and time are measured in the above mentioned
system of units. But we have to measure several other physical
quantities in our daily life . Hence, the international conference of the
scientists in 1960 AD decided to adopt a new system of measurement
which can measure all physical quantities. This system is called SI
system and the units used in this system are called SI units.

The system of the units that was adopted by the international
convention of scientist in 1960 AD in France is called SI system. The
units of measurement which are used in SI system are called SI units.

The full form of SI units is ‘system international de units’. The SI
system is the extended and improved form of MKS system and is
used all over the world.

The SI units are divided into two groups. They are fundamental units
and derived units.

Fundamental units

The units which do not depend on other units are called fundamental
units. The fundamental units are also known as basic units. The unit
of mass, length, time, temperature, etc are fundamental units. The
fundamental units are given in the following table :

S.N. Fundamental quantities Fundamental units Symbol
1 Length Metre m
2 Mass kg
3 Time Kilogram s
4 Temperature Second K
5 Electric Current Kelvin A
6 Amount of Substance Ampere mol
7 Luminous Intensity Mole cd
Candela

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Derived units

The units which can be expressed in terms of two or more fundamental

units are called derived units. In derived units, same fundamental unit

may be repeated or different fundamental units may be multiplied or

divided. The units of velocity, area, volume, etc can be derived from

the basic units of length and time. So, they are derived units. For

example:

Velocity = Distance travelled in a particular direction
Time taken

Here, unit of distance travelled is metre (m) and that of time taken

is second (s). So,

∴ V= m
s

Since the unit of velocity consists of two fundamental units, it is a
derived unit. The physical quantities which have derived units are
called derived quantities.

The unit of area is also a derived unit. It can be represented as:

Area = length x breadth
or, A = m x m = m2

Since the fundamental unit metre (m) is repeated twice, the unit of
area is a derived unit .

The derived units of some more physical quantities are given in the
table below:

S.N. Physical quantities Units Symbol

1 Volume Cubic metre m3

2 Speed Metre per second m/s

3 Acceleration Metre per square second m/s2

4 Force Newton N

5 Work Joule J

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Measurement of length

The shortest distance between any two points is called length. The
SI unit of length is metre (m). Different instruments can be used to
measure length. For example, a ruler or scale is used to measure a
short distance, a metre rod or a measuring tape is used to measure
the long distance, etc.

We use different units to measure different distances. Some of the
units such as millimetre (mm), centimetre (cm) and decimetre (dm) are
smaller than the unit metre (m). Such units are called sub-multiples
of metre (m). Similarly, the units decametre(dam), hectometre (hm)
and kilometre(km) are larger than metre (m). Such units are called
multiples of metre (m).

0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 56

Scale Measuring tape

Multiples and sub-multiples of metre

The relation of metre (m) with its sub-multiples and multiples is
shown in the following table:

10 millimetres (mm) = 1centimetre (cm)
10 centimetres (cm) = 1decimetre (dm)
10 decimetres (dm) = 1metre (m)
10 metres (m) = 1decametre (dam)
10 decametres (dam) = 1hectometre (hm)

10 hectometres (hm) = 1kilometre (km)

Precautions while measuring the length

Small lengths can be measured by using standard scale. But there
may be some errors or mistakes during measurements due to the
following reasons :

1. Due to the wrong position of the scale: If the scale is not placed
over the measuring side properly, it gives wrong reading. So, the

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measuring scale should be placed in close contact as well as parallel

to the measuring side.
û
12 13 14 15 ü
5 6
9 10 11 0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 56
4 56 78 4
2 3
23
0 cm 1 1

2. Error due to the use of damaged scale: If the beginning end of the
scale is damaged, the measurement should be started from the
particular number. Otherwise there will be error in reading due to
wrong position of zero(0).

ûü

0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 56 1 2 3 4 56

3. Error due to wrong angle of observation: The eyes of the observer
must be in front of the reading.

üû

0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 56 1 2 3 4 56

4. Sometimes the scales are wrongly built: Such scales give wrong
reading while measuring the length of things. So, we should be
careful while buying scales or tapes.

ûü

1 cm 0 4 3 7 5 6 7 4 9 11 11 12 13 14 15 0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 56 1 2 3 4 56

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Activity 1.3

Divide the class into the groups of four or ve students each and
order them to measure the following things accurately. Compare the
work of one group with that of other.

S.N. Things Length Breadth Height or Thickness
1. Science book
2. Science note book
3. Desk or bench
4. Classroom

Measuring the external diameter of spherical objects

Place a spherical object over a plane surface. Take two wooden blocks
with smooth edges. Then place the spherical object between the
wooden blocks so that the object is just touched by both the blocks.
Now, measure the distance between the wooden blocks. This distance
gives the external diameter of the spherical object.

0 cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 56

Measurement of volume

We use different liquids such as water, milk, petrol, diesel, kerosene,
alcohol, etc. The amount or quantity of these liquids is regarded as
their volume. When a liquid is placed in a vessel, it occupies some
space. The space occupied by a matter is called volume. The volume
of liquid is measured in the unit of litre (l). A little quantity of volume
is measured in the unit millilitre (ml).

1 litre = 1000 millilitres (ml)

The volume of the regular solids is measured in the unit cubic metre (m3).

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But the volume of liquids is measured in the unit litre. Cubic metre and
litre are related as:

1 cubic metre (m3) = 1000 litres(l)

Volume of solids

It is easier to measure the volume of regular solids. The volume of
a cuboid solid is determined by measuring its length, breadth and
height.

Volume = l × b × h

Activity 1.4

Measure the length, breadth and height of your science book and
calculate its volume.

But the volume of irregular solids cannot be determined by using
the formula. Their volume is determined with the help of measuring
cylinder .

Activity 1.5

Observe the levels of different liquids in a measuring cylinder.
Take a measuring cylinder and pour some water into it. Then observe
the surface of water carefully.
What will you observe ?
You will see that the level of water is depressed at the middle. The
water level at the side is raised little above. It is because water wets
the walls of the vessels. The surface of liquid which is raised at the
side and depressed in the middle is called concave meniscus. The
liquids such as water, oil, kerosene, alcohol, etc form the concave
meniscus. We should observe the volume of such liquids by keeping
eyes straight to the lower meniscus of the liquid level.

û

ü

û

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Some liquids like mercury do not wet the walls of vessels. In such
liquid, the middle part is raised up while the sides are depressed
down. Such meniscus is called convex meniscus.

Activity 1.6

Measure the volume of a piece of stone.

Take a measuring cylinder lled
with water upto its half part.
Note down the volume of water.
You should observe the water
level by keeping eyes straight
to the lower meniscus in the
measuring cylinder. If the eyes
are above the surface of water,
the volume of water will be seen
more. Similarly, if the eyes are
below the water level the volume
will be seen less.

Now, tie a small piece of stone with a piece of thread and dip it into
the measuring cylinder .

What will you observe ?

The level of water in the measuring cylinder increases. Note down
the new volume in the cylinder. Hence,

Initial volume of water in the measuring cylinder (v1) = 50ml

Volume of the water after dipping the stone(v2) = 70ml

Therefore, volume of the stone (v) = v2 —v1=70ml-50ml= 20ml

Measuring the volume of a gas

It is difcult to measure the exact volume of gases because the gases
are compressible. A measuring cylinder can also be used to measure
the volume of a gas.

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Activity 1.7

Measure the volume of a gas present in the balloon.

Take a water trough and ll water up to its two-thirds. Then ll a
measuring cylinder completely with water and place palm over it.
Invert the cylinder in the water trough and remove your palm slowly.
Now, dip the balloon inside the water trough and open the mouth of
the balloon to let air enter the measuring cylinder. The air released
from the balloon occupies some space inside the measuring cylinder.
This makes the water level fall down in the measuring cylinder. The
volume of the space occupied by the air inside the measuring cylinder
gives the volume of gas.

Measurement of time

The interval between any two events called time. The time is measured

with the help of watches and clocks. The basic unit of time is second

and the other units are minute, hour, day, week, etc .

60 seconds = 1 minute

60 minutes = 1 hour

24 hours = 1 day

7 days = 1 week
52 weeks = 1 year

365 days = 1 year

There are 366 days in a leap year. The year in which the month
February is of 29 days is called leap year.

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Main Points to Remember

1. The comparison of unknown physical quantity with a known
or standard quantity is called measurement.

2. The quantities which can be measured are called physical
quantities.

3. The system of measurement in which length is measured in
metre, mass is measured in kilogram and time is measured in
second is called MKS system.

4. The system of measurement in which length is measured in
centimetre, mass is measured in gram and time is measured
in second is called CGS system.

5. The units which cannot be split into other simpler units are
called fundamental units.

6. The units which can be expressed in terms of two or more
fundamental units are called derived units.

Exercise

1. Choose the best alternative in each case.

a. Mano, Pathi and Dalo are the traditional Nepalese instruments
to measure

i. Area ii. Mass of grains
iii. Volume of grains iv. Length

b. Which of the following is a physical quantity?

i. Temperature ii. Anger

iii. Hatred iv. Affection

c. Which of the following is a traditional tool to measure length in
Nepal?

i. Footstep ii. Arm

iii. Hand span iv. All of these

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d. Which of the following is a derived quantity?

i. Quantity of matter ii. Speed

iii. Temperature iv. Time

e. How many days are there in a leap year?

i. 365 days ii. 365 ½ days

iii. 366 days iv. 365.25 days

2. Answer these questions in very short:
a. What is measurement ?
b. What do you mean by physical quantities? Give examples.
c. What is the SI unit of temperature ?
d. How many seconds are there in a day ?
e. What is the CGS unit of length ?

3. Dene the following terms:

a. CGS system b. FPS system c. MKS system
f. Derived units
d. SI system e. SI units

4. Give reasons:
a. The unit of area is a derived unit.
b. The unit of length is fundamental unit.
c. Hand span and footsteps are not reliable units.

5. Convert the following:
a. 5kg into grams.
b. 1day into minutes.
c. One year into hours.
d. 50 cm into kilometre.
e. 1000 metres into centimetres.

(Answers: a. 5000 g b. 1440 min. c. 8760 hrs. d. 0.0005 km. e. 1,00,000 cm)

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6. Answer in brief:
a. Explain the importance of measurement.
b. Write down differences between fundamental and derived units.
c. How do you measure the volume of an irregular solid? Explain
with an example.
d. Describe concave and convex meniscus with diagrams.
e. Enlist the precautions that should be taken while measuring
the length.

Project Work

Collect different things such as science book, brick, stone, a glass
of water, air-lled balloon, etc and measure their volume using
appropriate devices or formula. Present your ndings in a table
and show your teacher.

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Chapter

2 FORCE AND MOTION
Estimated periods:5

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü dene rest and motion;
Ü dene force and mention its measurement and unit;
Ü explain effects of force;
Ü dene speed and velocity.

MIND OPENERS
Ü Are you in rest or motion state now?
Ü How do you pull water from well?
Ü What happens when you kick a ball?
Ü How can you stop a moving ball?

Rest and Motion

Have you seen birds ying in the sky, water owing in river, vehicles
running on the road? Here, birds, water and vehicles are changing
their positions. They are said to be in motion state.

When you walk or travel by bus, you change your position continuously.
At this time the surrounding, trees, house, buildings, road, etc remain
in their own positions. They are not changing their positions with
time. Thus, you are in motion state whereas trees, house, buildings
and road are in rest state.

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A body is said to be in motion if it changes its position with respect to
its surrounding.

A body is said to be at rest if it does not change its position with
respect to its surrounding.

Rest and motion are relative terms. A body can be in motion when
compared to one body and can be at rest at the same time when
compared to another body. For example, when you are traveling by
bus, you change your position as compared to outside road, trees,
buildings, etc. Therefore, you are in motion in such case. At the same
time, when you are compared with your fellow passengers, you are in
same position with respect to them. Therefore, you are in rest in such
case. Thus, you seem to be in both motion and rest states. It depends
upon comparison. Therefore, rest and motion are relative terms.

Types of motion

There are various types of motion. Some of them are discussed below:

1) Linear motion 6) Spiral motion

2) Circular motion 7) Vibratory motion

3) Rotatory motion 8) Curvilinear motion

4) Oscillatory motion

5) Random motion

Linear motion (Translatory motion)

When a body moves in a straight line in a particular direction,
its motion is called linear motion. It is also known as translatory
motion. For example, motion of vehicles in a straight road, motion of
aeroplane, motion of stone released from a catapult, a stone dropped
from a height, etc. Gravity also produces translatory motion.

Linear motion of a car

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Circular motion

When an object moves in a circular
path, its motion is called circular
motion. In this motion, the distance
of the object from the centre remains
xed. For example, motion of hands
of watch, movement of the earth
around the sun, etc.

Circular motion of the earth

Rotatory motion

When an object moves around its own axis, its motion is called
rotatory motion. For example, movement of the earth around its axis,
movement of Janto around the rod xed in the middle, motion of a
spinning top, motion of blades of fan, etc.

Spinning top Janto Blades of fan

When an object moves in to and fro motion, its motion is called
oscillatory motion. In this motion, the object moves forward and then
backward. For example, motion of pendulum, motion of swing, etc.

Oscillatory motion

When an object moves in any direction without showing a particular
motion, its motion is called random motion. For instance, movement
of football player in the ground, movement of smoke and dust particles
in air, etc.

Motion of a swing 18 Motion of a pendulum
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Activity 2.1

To show oscillatory motion

Materials required: a stone, a thread, etc.

Procedure
i. Take a stone and tie it to one end of a thread.
ii. Fix another end of the thread to a stand.
iii. Gently pull the stone. Then release it. What happens?

Observation: The stone moves forward and backward periodically.
Conclusion: The motion of the stone is oscillatory motion.

Random motion

When an object moves in any direction without showing a particular
motion, its motion is random motiom. For instance, movement of
football player in the ground, movement of smoke and dust particles
in air, etc.

Random motion of a football Random motion of a ball Random motion of a buttery

Spiral motion

When bicycle runs, the wheel of the bicycle rotates about its axis
as well as in a straight line on the road at the same time. Thus,
the wheel has both rotatory and linear motion at the same time.

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The motion of a body having both linear and rotatory motion at the
same time is called spiral motion.
A screw driver used to tighten a screw nail, a boy stepping up a
winding staircase, etc are example of spiral motion.

Use of screw driver Winding staircase Use of jack screw

Vibratory motion

When a string of a guitar is plucked, it vibrates. Similarly, when
prongs of a tuning fork are hit to a rubber pad, they vibrate. Here,
the motion of string or prongs is vibratory motion. Hence, the rapid
to and fro motion of an object is called vibratory motion or vibration.

During vibratory motion, the object has a very fast oscillatory motion.

Vibration of tuning fork Guitar

Curvilinear motion Motion in a curved path
Book 6
When direction of a moving body
changes continuously, its motion is
called curvilinear motion. Vehicles on
the curved road takes several turns, we
take several turns while moving on the
sloppy road, etc. These are the examples
of curvilinear motion.

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Force

We do various types of works in our daily life. We open door, lift load,
carry books, push carts, etc. In order to do all these works, we have
to apply force. Similarly, we need force to stop a moving object. We
apply force by pushing or pulling the objects. We push carts, or doors.
We pull water from well or pull doors, etc.
Force changes the state of bodies from rest to motion or from motion to
rest. When we apply force to an object at rest, it comes to motion state.
Similarly, when we apply force to a moving object, it comes to rest.
Thus, force can be dened as an external agent, which changes or
tries to change the state of body from rest to motion or motion to rest .
The SI unit of force is Newton and CGS unit is Dyne. In short, Newton
is denoted by N.
The force required to pull or push an object of mass 100 g is equal to 1
Newton. Similarly, the force required to pull or push 1 kg object is 10N.

Activity 2.2

Take an object of mass 1 kg and suspend it to the hook of
spring balance. Observe the reading.
Observation: You will observe the reading of 10N in the
spring balance.

Effects of force

Force has following effects:
1. Force can change the states of objects:

When you kick a ball at rest it comes to
motion. A goal keeper catches a moving
ball and brings it into rest state.
2. Force can change the shape and size of
objects: When you pull rubber band, it gets
stretched and its size increases. When you
squeeze toothpaste, its shape changes. Thus,
force changes shape and size of objects.

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3. Force can change direction of motion:
When a batsman hits cricket ball, the
direction of the ball changes. Similarly,
when a football player kicks a moving ball its
direction changes. Thus, the force changes
the direction of a moving object.

4. Force can change speed of a moving
body: A moving bicycle runs faster when it
is pushed from backside and it moves slower
when it is pulled from backside. Similarly,
a rolling ball moves faster when it is kicked
to the same direction.

Activity 2.3

To demonstrate that force can change the state of rest or motion

Keep a ball on the ground, the ball is in
the rest state. Kick the ball with your
leg. The ball comes to motion. Here,
change in the state of the ball from
rest to motion is due to the force applied
while kicking the ball. In the same way,
when you catch the moving ball, it comes
to rest.

Speed

Suppose a body moves from one place to another either in a straight
or curved path and covers 20 meter distance in 2 seconds, we can say
that it covers 10m distance in 1 second and its speed is 10m/s.
Speed is dened as the distance covered by an object in unit time.

Speed = Distance covered (d)
Time taken (t)

Since, distance is measured in meter and time in second. Speed is
measured in meter per second (m/s). It is also measured in kilometer
per hour (km/hr).

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Velocity

When a body moves from one point to another point in a particular
direction, its speed is called velocity.
Therefore, velocity can be dened as speed in a particular direction.
Since the distance in a particular direction is displacement, velocity
can be dened as displacement covered in unit time.

Velocity =DTiismpleactaekmeennt
Since unit of displacement is meter and that of time is second, the
unit of velocity is meter per second (m/s).
Comparison of speed and velocity

Suppose a body moves from point A to B
and then to point C. The distance of AB
and BC is 4m and 3m respectively. Thus,
the total distance is 7m. Suppose, the total
time taken by the body is 2 seconds.

The speed of the body is calculated by using formula

Speed = Distance covered (d)
Time taken (t)

= 4 + 3
2

= 3.5 m/s

If the body moves directly form A to C, its displacement is 5m.
Therefore, the velocity of the body is calculated by using formula,

Velocity=DisTpilmaceetmakenent (d)
(t)

= 5
2

= 2.5 m/s

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Worked out example
A man travels 240 m distance in 1 minute. Calculate his speed.

Solution:

Distance (d) = 240m

Time (t) =1 minute = 60s

Speed (v) = ?

We have, Distance covered (d)
Time taken (t)
Speed =

= 24060
= 4 m/s

Therefore, the speed of the man is 4m/s.

Main Points to Remember

1. A body is said to be at rest if it does not change its position
with respect to its surrounding.

2. A body is said to be in motion if it changes its position with
respect to its surrounding.

3. Linear motion, circular motion, rotatory motion, oscillatory
motion and random motion are various types of motion.

4. Force is an external agency that changes or tries to change
the state of motion or rest of an object.

5. Force can change:

i) state of rest or motion

ii) shape and size of an object

iii) direction of an object

iv) speed of motion

6. Speed is dened as the distance covered by an object in unit
time.

7. Velocity is dened as the displacement travelled in unit time.

Times' Crucial Science and Environment 24 Book 6

Exercise

1. Choose the best alternative in each case.

a. Rest and motion are ………… terms.

a. Absolute b. Relative

c. Linear d. Non-conditional

b. Which of the following has a rotatory motion?

a. Janto b. Spinning top

c. Blades of fan d. All of these

c. To and fro motion of a body

a. Translatory motion b. Oscillatory motion

c. Circular motion d. All of these

d. Which of the following has a vibratory motion?

a. Top b. Pendulum

c. Screw driver d. None of these

e. The displacement of a body per unit time is called

a. Velocity b. Speed

c. Distance d. Motion

2. Copy the correct statements and correct the false statements
if any:

a. A stone thrown upward moves in rotatory motion.

b. A body at rest state does not change its position with respect
to its surrounding.

c. Rest and motion are relative terms.

Times' Crucial Science and Environment 25 Book 6

d. When an object moves in a circular path, its motion is
rotatory motion.

e. A moving bicycle moves faster when it is pulled from
backside.

3. Identify the types of motion of following objects:

Motion of Rote Ping, motion of a bird, motion of a pendulum,
motion of plucked string of guitar, motion of wheel of bicycle,
motion of the earth around the sun

4. Dene: b) Rest c) Force
a) Motion

5. Give short answers:
a. What is motion? Give some examples of objects that are in
motion state.

b. What are various types of motion?

c. What is linear motion? Give some examples.

d. What is rotatory motion? Give some examples.

e. What is force? Dene 1 Newton force.

f. What are effects of force?

6. Comprehensive questions:
a. Rest and motion are relative terms. Explain.

b. Motion of a buttery ying in a garden is random motion.
Explain.

c. Explain the effects of force.

7. Solve the following numerical problems:

a. Ram covers a distance of 200m in 50 seconds. What is his
speed?

b. A vehicle travels a distance of 20 km in an hour. Find its
speed.

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8. Diagrammatic question:
a. Study the diagram and answer the questions:

I II III
i. What kinds of motion are performed in gure I and II?
ii. What effects of force are shown by gure III?
iii. Dene the motion involved in gure I and II.

b. Draw a diagram to show the motion of a pendulum.

Project Work

i. Observe a moving bicycle. Name the types of motion shown by
different parts of the bicycle.

ii. Observe a football match. Mention the various effects of force
that you observe when football player hits the football.

Times' Crucial Science and Environment 27 Book 6

Chapter

3 MACHINE
Estimated periods:4

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü identify simple machines and dene them;
Ü enlist the advantages of simple machine in daily life;
Ü classify the different types of simple machines.

MIND OPENERS
Ü What do you use to chop vegetables?
Ü What do you use to cut paper ?
Ü How do you open the lid of cold drink bottle?
Ü What are such instruments called ? Why do you use such

instruments? Discuss.

Introduction

We perform several work in our daily life. During our work, we can
use different instruments and tools to make our work easier and
faster. Some of these tools are simple in structure and are called
simple machines. Thus, the simple devices which make our work easier
and faster are called simple machines. Broom, nail cutter, scissors,
crow-bar, bottle opener, etc are some examples of simple machines.
Some of the machines that we use are very complex in structure.
Such machines are called complex machines and are made up of large
number of simple machines. Motorcycle, bus, crane, sewing machine,
etc are some examples of complex machines.

Sewing machine Motorcycle Crane
Book 6
Times' Crucial Science and Environment 28

Advantages of simple machines

We can perform our task faster and more conveniently by using
simple machines. The simple machines make our work easier in the
following ways:

1. Simple machines multiply the applied force
We can lift a heavy load by using
less effort in a simple machine.
For example, you must have
seen the use of a screw jack to
lift the vehicles while changing
their wheel. Similarly, we can
lift a heavy piece of a rock by
using a crow-bar.

In the above examples, if we
try to lift the vehicles or the
pieces of rocks without suitable
machine, we cannot lift them. But we can easily lift them with the
help of simple machines because the simple machines multiply our
applied force.

2. Simple machines increase the speed of doing work
If you try to transport bricks from one place to another by carrying
them on hands, it will take more time. But you can transport
several bricks at a time by using a wheel-barrow. Thus, the
wheel-barrow makes your work faster. It means that the simple
machines increase the speed of doing work.

Wheel barrow Use of bottle opener Use of door knob
Book 6
Times' Crucial Science and Environment 29

3. Simple machines transfer force from one point to another
Have you ever opened the lid of a can ? How do you open it ?
Can you open the lid of the can with your ngers only ?
The answer is probably ‘no’. But you can easily open the lid if you use
the long stem of a spoon or a knife.

A

B

In the gure, effort (force) is applied in the lid of the can at point ‘A’
of the spoon but the spoon opens the lid of the can at point ‘B’. Here,
the force is transferred from point ‘A’ to ‘B’ of the spoon.

4. Simple machines change the direction of the applied force

A pulley can be used to lift heavy objects.
It can also be used to draw water from
a well. If you pull the rope of the pulley Wooden disk

downwards, the bucket will be pulled Rope
upwards. In this case, the direction of the
force is changed by the pulley. Thus, the L

simple machine makes our work easier E
by changing the direction of the applied
force.

Types of simple machines

The simple machines can be classied into six types on the basis of
structure and function. They are:

1. Lever 2. Pulley

3. Wheel and axle 4. Inclined plane

5. Screw 6. Wedge

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1. Lever
A lever is a long rigid bar that is capable of rotating about a xed
point. The xed point about which a lever rotates is called fulcrum. A
lever consists of three main parts - load, effort and fulcrum. The load
is the object that has to be lifted by the lever whereas the effort is the
force applied to the lever to lift the load.

effort distance

dilsotaadnce Fulcrum

The advantage of the lever depends upon the load distance and effort
distance. In a lever, the distance between the fulcrum and the load
is called load distance (Ld) or load arm (La) whereas the distance
between the fulcrum and the effort is called effort distance (Ed) or
effort arm (Ea).

The lever can be classied into three types on the basis of position of
load, effort and fulcrum. They are:

a. First class lever

The lever in which the fulcrum lies at any point in the middle of load
and effort is called rst class lever. Crowbar, scissors, see-saw, beam
balance, dhiki, cutting shears, etc are some examples of rst class
lever.
F

E L LE
F

Crowbar L Scissors Beam balance
E L
EF L
F F Dhiki
E Book 6

See-saw Metal cutting shears

Times' Crucial Science and Environment 31

b. Second class lever
The lever in which the load lies at any point in the middle of effort
and fulcrum is called second class lever. In the second class lever,
the effort distance is always greater than the load distance. Hence,
the second class lever multiplies effort more than any other class of
lever.

Wheel-barrow, nut-cracker, bottle opener, paper cutter, etc are some
examples of second class lever.
FL
E E
L

F L E
Wheel-barrow F Bottle opener

F Onion cutter E
LE LF
LF
Nut cracker E Mango cutter

Paper cutter

c. Third class lever
The lever in which effort lies in the middle of load and fulcrum is
called third class lever. Such lever makes the work safe and easy.
But it cannot multiply effort because the load distance is always
greater than the effort distance.

Fire tongs, stapler, broom, shovel, shing rod, spoon, etc are the
examples of third class lever.

Times' Crucial Science and Environment 32 Book 6

E F E L
L F
E
F L Fire tongs
Fishing rod
Broom

E F E F
L F E
L
Stapler Shovel L

Spoon

2. Pulley

A pulley is a hard metallic or wooden disc with a grooved rim. A rope
moves around the groove of the disc. The load is tied to one end of the
rope and it is pulled from another end of the rope by applying effort.

Wooden disk E Rope
Rope Wooden disk

LL

E Single movable pulley
Single xed pulley

A pulley can be classied into two types-single xed pulley and single
movable pulley. In a single xed pulley, a circular disc is xed at a
point. The disc can rotate about the axle. But in a movable pulley,
one end of the rope is tied to a rigid support and the effort is applied
from other end of rope. The circular disc moves along with load.

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Combined pulley

A pulley which consists of a combination of two or more pulleys is
called combined pulley. A combined pulley is also called compound
pulley or block and tackle.

Wooden disk Fixed pulley
Rope
E
Movable pulley L

Combined pulley

3. Wheel and axle

A wheel and axle is a simple machine which consists of two wheels
(cylinders) of different diameters. The larger cylinder or wheel is
xed rigidly with the small wheel in such a way that both the wheels
spin about the same axis. Generally, load is lifted by the small wheel
and the effort is applied on the big wheel.

Wheel

Wheel Axe Wheel
Axe Kite string reel Steering of car

screw driver

Door knob, wheel of vehicle, steering of a vehicle, screw driver, etc
are the examples of wheel and axle.

Times' Crucial Science and Environment 34 Book 6

4. Inclined plane

A slanted surface over which load can be pulled or pushed is called
inclined plane. In general, it is a sloping surface. Winding roads on
hills, spiral staircase, wooden plank used for loading goods in a truck,
ramp used in hospitals, etc are some examples of inclined plane.

Wooden plank rested against truck Inclined Plane

5. Screw

A screw is a simple machine which seems to have an inclined plane
wrapped around a cylindrical surface. Jack screw, screw nail, driller,
etc are the examples of screw. A jack screw is used to lift vehicles
while changing their wheels.

Screw nail Driller Jack screw
Book 6
6. Wedge

A wedge is a simple machine which has a
sharp part at one end and at part at the
other. The effort is generally applied upon
the at part and the sharp part performs
the work. A wedge is used to split the
wooden logs. Axe, knife, khukuri, nail,
chisel, needle, etc are also the examples
of wedge.

Times' Crucial Science and Environment 35

Main Points to Remember

1. The simple devices which make our work easier and faster
are called simple machines.

2. The simple machines can be categorized into six types:
pulley, wheel and axle, inclined plane, screw and wedge.

3. A long rigid bar that is capable of moving about a xed
point is called lever.

4. A lever may be- rst class lever, second class lever or third
class lever.

5. A pulley is a round metallic or wooden disc with a grooved rim .
6. Wheel and axle consists of a large cylinder xed rigidly with

a small cylinder. The large cylinder is called wheel and the
small cylinder is called axle.
7. A slanted surface over which load can be pulled or pushed is
called inclined plane.
8. A wedge is a simple machine which has a sharp part at one
end and at part at other end.

Exercise

1. Choose the best alternative in each case:

a. The xed point about which a lever rotates is called

i. Load ii. Effort

iii. Fulcrum iv. Mechanical advantage

b. Which of the following is a rst class lever?

i. Broom ii. Nut-cracker

iii. Nail-cutter iv. None of these

c. Winding road in a hill ii. Inclined plane
i. Pulley iv. Screw
iii. Wheel and axle

Times' Crucial Science and Environment 36 Book 6

d. Screw driver ii. Wedge
i. Screw iv. Pulley
iii. Wheel and axle
ii. Second class lever
e. A Dhiki is a iv. None of these
i. First class lever
iii. Third class lever

2. Answer these questions in very short:
a. What is a simple machine ?
b. Why do we use simple machines ?
c. On what basis are the levers classied ?
d. What is a fulcrum ?
e. Why is crowbar a rst class lever ?

3. Dene the terms: b. Single movable pulley
a. Pulley d. Axle
c. Wheel

4. Give reasons:
a. We use tongs to catch a burning piece of a coal.
b. We use a pulley to draw water from a well.
c. A second class lever multiplies the effort more than other levers.

5. Differentiate between:
a. Pulley and wheel and axle.
b. Simple machine and complex machine

6. Classify the following levers:

crowbar, wheelbarrow, see-saw, nail-cutter, bottle opener, re
tongs, beam balance, nut-cracker, shovel

Times' Crucial Science and Environment 37 Book 6

7. Answer these questions in detail:

a. What are the advantages of simple machines ?

b. How can you prove that a simple machine changes the
direction of effort ?

c. What is a lever ? Explain with the help of a diagram.

d. Explain the structure of a wheel and axle with the help of a
diagram.

e. What is a pulley ? How does it help in lifting weight ?

f. What is an inclined plane ? How is it useful ?

8. Draw the well-labelled diagrams of the following:

a. Inclined plane b. A second class lever

c. Single xed pulley d. Single movable pulley

Project Work

Observe different instruments that are being used at your home
and make a list of them. Which of them are simple machines?
Classify them into different types. Also draw their diagrams.

Times' Crucial Science and Environment 38 Book 6

Chapter

4 HEAT
Estimated periods:7

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü dene heat.
Ü tell and explain sources of heat.
Ü explain effects of heat.
Ü explain uses of heat.
Ü explain the meaning and uses of absorption of heat.

MIND OPENERS
Ü What do you use to cook food?
Ü What happens to ice when you heat it?
Ü What happens if there is no sun?
Ü Can you say some uses of heat?

Introduction

When there is cold in winter, you want to sit near the re or in the
sunshine. You feel warm when you move towards the re. Fire and
the sun give us heat.
Thus, heat is a form of energy which gives the sensation of warmth.
The SI unit of heat is Joule (J). It can be measured in calorie also.

1 calorie = 4.2 Joules.
Heat is needed to run vehicles, engines, etc. It is also needed to keep
our body warm. We use solar heat for drying clothes, food grains,
pulses, etc.
Heat is used to turn water into steam and run engines. For example,
steam engine which was invented by James Watt used to work by the
steam that is produced from water after heating.

Times' Crucial Science and Environment 39 Book 6

Sources of heat

There are various sources of heat. Some of the sources of heat are as
follows:

a) The sun b) Fuels c) Electricity

d) Friction e) Combustion of food in the body

The sun

The sun is the main source of heat. All
animals and plants get heat from the sun.
The heat of the sun is called solar heat.
We use solar heat for drying clothes,
drying crops and food grains. Plants use
solar energy for the preparation of food by
photosynthesis process. Animals get their
foods from plants. Thus, all animals and
plants use solar heat.

Activity 4.1

Take a hand lens and focus sunlight on a piece of paper by moving
the lens closer or farther. Keep the lens in the same condition for a
while. What happens to the paper?

Observation: The paper burns due to the solar heat focused on the
paper.

Conclusion: If the heat of the sun is focused at a point, it can burn
the things.

Fuels

Fuels like petrol, coal, diesel, kerosene, rewood, cake of cattle dung,
gobar gas, etc are also the sources of heat. Heat can be produced by
burning these fuels. Heat of the fuels is used to cook food, to run
vehicles, machines, etc.

Times' Crucial Science and Environment 40 Book 6

Candle Fire Burning coal

Electricity

We use electrical energy to run electric heater, rice cooker, electric
bulb, micro oven, toaster, etc. These devices are used to produce heat.
We use electric heater in winter season to make our rooms warm. We
use rice cooker, micro oven, etc to cook food.

Bulb Electric heater Rice cooker

Friction

You must have seen the burning of match stick when it is rubbed
over match cover. Similarly, you must have experienced warmth
produced when your two palms are rubbed with each other. In both
cases heat is produced by friction.

When one body is rubbed with another body, friction is created.
Friction produces heat.

Activity 4.2

Rub your two palms for a few seconds and
put them on your cheek. What do you feel —
warm or cold?

We get heat by rubbing match stick with the surface of match box and
by rubbing two stones.

Times' Crucial Science and Environment 41 Book 6

Combustion of food

Our body is warm. This is due to the heat produced from food inside
our body. The food reacts with oxygen inside mitochondria of cell,
and heat energy is produced. This heat keeps our body warm.

Effects of heat
Heat has following effects.

i. Heat causes rise in temperature of a body.
ii. Heat causes expansion of an object.
iii. Heat causes change in state of matter.

Heat causes rise in temperature of a body

When you heat an object, it becomes hotter. Becoming hotter means
rise in temperature.

Activity 4.3
To show that heat rises the temperature of a substance

Materials required: A beaker, stand, thermometer

Procedure
1. Take some water in a beaker.

2. Dip the bulb of thermometer inside the water to measure
temperature of the water.

3. Note the temperature.
4. Heat the water for two minutes. Now, observe the temperature.

What is your result? What conclusion do you get from the
activity?

Times' Crucial Science and Environment 42 Book 6

Observation: The temperature of water increases when it is heated.
Conclusion: The heat causes the rise in temperature of a body.

Heat causes expansion of an object

When an object is heated, it becomes larger. Becoming larger means
increase in volume. It is also called expansion of an object.

Activity 4.4
To show the expansion of a solid due to heat

Materials required: A metal wire, stand, candle, etc.
Procedure

1. Take a metal wire of length 30 cm and hang it between the
poles.

2. Stretch the wire between two poles as shown in the gure.
3. Heat the wire by burning candle for two minutes. What

happens? Let the wire cool down.

Observation: When the wire is heated, the wire hangs down due
to expansion. When the wire is cooled down, the wire
becomes stretched to the original form.

Conclusion: This activity shows that solid expands on heating and
contracts on cooling.

Times' Crucial Science and Environment 43 Book 6

Activity 4.5
To show expansion of liquid due to heat

Materials required: A round bottom ask, coloured water, a glass
tube, cork, etc.

Procedure
1. Take a round bottomed ask and
ll it with coloured water.
2. Insert a glass tube through a
cork as shown in the gure.
3. Heat the ask with burner or
spirit lamp. What happens?

Observation: The water rises in the
tube. The colour helps to nd the actual
level of water in the tube.

Conclusion: Liquid expands on heating.

Activity 4.6
To show expansion of gas due to heat

Materials required: A balloon, ask, trough, hot water, etc.

Procedure
1. Take a balloon.
2. Fix its mouth with the mouth of a ask as shown in the gure.
3. Keep the ask in the hot water. What happens?

Times' Crucial Science and Environment 44 Book 6

Observation: The balloon gets inated. This is due to expansion of
the gas contained in the vessel.
Conclusion: Gas expands on heating.

Heat causes the change in states of matter

When solid substance is heated, it changes to liquid. Similarly, when
liquid is heated, it changes to gas.
In the same way, gas changes to liquid and liquid changes to solid on
cooling.

Activity 4.7
To show change of state of matter due to heat

Materials required: Test tubes, ice cubes, burner, test tube holder etc.

Ice Water Water vapour

Procedure
1. Take some ice cubes in a test tube.
2. Heat the ice. What happens?
3. Heat the water further. What happens?

Observation: The ice (solid) melts into water when it is heated. The
water (liquid) changes to vapour (gas) on further heating.

Conclusion: Matter changes its state due to heat.

Absorption of heat

When we sit in the sun in hot sunny days wearing black clothes, we
feel hotter. When we wear white clothes, we do not feel such hotness.
In the same way, when we cook foods in the pots having black and

Times' Crucial Science and Environment 45 Book 6

rough base, the foods are cooked faster than in the pots having shining
and smooth base. Our hair is hotter than other body parts when we
walk or sit in the sun shine.

What are the reasons behind these observations?

Black and rough objects absorb heat easily. They are good absorbers
of heat. Whereas white, shining and smooth substances cannot absorb
heat as much as the black objects do.

The substances which absorb heat easily are called heat absorbers.
The black objects are good absorbers of heat.

Activity 4.8

To show that black objects are good heat absorbers

Materials required: Two beakers, black polish, brush, water,
thermometers, etc.

Procedure
1. Take two beakers.
2. Polish outside of one of the beakers
with black colour.
3. Fill half of both the beakers with
water.
4. Keep the both beakers in the sun
shine for about half an hour.
5. Measure the temperature of water
of both beakers. What will you
nd?

Observation: The water of black beaker gains higher temperature
than the water of another beaker.

Conclusion: Black substance is good absorber of heat. Therefore,
black substance can absorb more heat than other substances.

Uses of absorption of heat

Black and rough substances are good absorbers of heat. Therefore,
they are used in various types of heating devices.

Times' Crucial Science and Environment 46 Book 6