Blooming Science-7 (2077) final for press

Approved by Government of Nepal, Ministry of Education, Curriculum
Development Center (CDC).

Blooming

SCIENCE
&

ENVIRONMENT

Book

7

Authors
Raj Kumar Dhakal
Purushottam Devkota

Shubharambha Publication Pvt. Ltd.

Kathmandu, Nepal

Published by:

Shubharambha Publication Pvt. Ltd.

Kathmandu, Nepal
URL: www.shubharambhapublication.com
E-mail: [email protected]

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Blooming Science and Environment Book-7

Authors : Raj Kumar Dhakal

Purushottam Devkota

Video Content : Laxmi Nand Dhakal

Layout Design : Ram Malakar

Language Editor : Krishna Prasad Regmi

Copyright © : Publisher

Edition : 2077

© : Publisher

No part of this book may be reproduced or transmitted by means (electronic, photocopying,

recording or otherwise) without prior written permission from the publisher. Any breach

of this condition will entail legal action and prosecution.

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That’s why we teamed with Freelancer Company Pvt. Ltd. and Mr. Laxmi Nand Dhakal
to create an immersive experience to redefine how we learn. With Laxmi Sir’s brains
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video materials that aid the topics covered in this textbook.
We hope to make learning fun again! With a few clicks, you will be able to learn more

about any topic in this book via practical experiment videos.

Freelancer Company Pvt. Ltd. Laxmi Nand Dhakal
IT Company in Kathmandu Scientist, Teacher, HOD (R&D Dept)
https://creativescienceproject.com
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Academic Director Kathmandu, Nepal



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1. Android:

a. Open this link on your browser on your Android phone (using
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Preface

The series Blooming Science and Environment has been brought out as an
indispensable resource for school level students and has intended to provide concise
and comprehensible explanation of key concepts, facts and principles across science
disciplines. Organized around the National Science curriculum prescribed by
Curriculum Development Centre, Sanothimi, Bhaktapur, the series presents solid
overviews of the most commonly encountered school science topics with sound
academic and fun activities.

The clear and accessible definitions, concise language, helpful diagrams and
illustrations and other science activities offered in this series will nonetheless help
teachers understand science concepts to the degree to which they can develop
rich and exciting inquiry approaches to exploring these concepts with students in
the classroom. As the series has been brought out considering the age and other
psychological factors of children, the learning materials in this series appeal to the
sense of the children and they are related to the world of young learners. Activities
with varieties of questions in this series are meant to assess and evaluate the level of
students’ inquisitiveness.

As each unit begins with its objectives and estimated teaching periods which help
teachers to complete the course in time. Moreover, each lesson in the series ends
with Let's Learn, Points to Remember and Boost Up Exercises; these two sections
are meant to provide good review to students and enhance their ability to solve the
exercise questions. Each lesson has Multiple Choices Questions, Project Work that are
meant to arouse more creativity and interest in the students for better understanding
and adjustment with their scientific world.

We are grateful to students, parents and principals who shared their valuable
suggestions in materializing this series. Any constructive suggestions and
recommendations for the betterment of this series will be highly acknowledged.

AUTHORS

Contents

PHYSICS
1. Measurement ..................................................................................7
2. Force and Motion...........................................................................21
3. Simple Machines ...........................................................................39
4. Pressure ..........................................................................................47
5. Energy, Work and Power ...............................................................54
6. Heat.................................................................................................65
7. Light ...............................................................................................77
8. Sound .............................................................................................87
9. Magnetism .....................................................................................96
10. Electricity ....................................................................................106
CHEMISTRY
11. Matter............................................................................................116
12. Mixture and Solution ...................................................................130
13. Metals and Non-metals ................................................................144
14. Some useful Chemicals ................................................................153
BIOLOGY
15. Living Beings ..............................................................................159
16. Cells .............................................................................................195
17. Life Process in Plants ..................................................................205
ASTRONOMY & GEOLOGY
18. Structure of Earth .........................................................................224
19. Weather and Climate ...................................................................233
20. The Earth and Space ....................................................................243
ENVIRONMENT SCIENCE
20. Environment and Balance of Environment .................................253
21. Environment Degradation and Its Conservation ........................268
22. Environment and Sustainable Development ................................287
Practical Worksheet .....................................................................296
Model Question ...........................................................................298
List of Video Experiments ...........................................................300

1Chapter Measurement

Learning Outcomes

On the completion of this unit, students will be able to: Estimated Periods: 5+1

• introduce SI system of measurement and use SI units of fundamental

quantities.

• measure area of regular and irregular plane surfaces.

• measure volume of regular and irregular solids.

• tell method of measurement of volume of liquid and to measure it.

• solve numericals related to area, density and volume.

Introduction

Measurement plays an important role to make our life comfortable. When we ask for
one kilogram of , the paper weighs it by using a physical balance. What happens if
he gives us one kilogram of potatoes by estimation and not by weighing? We may get
more or less amount of potatoes than what we want i.e. one kilogram.

Merely by estimation, we can get only a rough and inaccurate idea about the quantities
like mass, length, time, etc. Therefore, to take accurate measurement of a quantity we
use standard quantity.

Measurement is the comparison of an unknown quantity with a known standard
quantity.

For the measurement of quantities, we use different methods and devices. We need
some devices like a scale to measure length, a watch to measure time and a beam
balance with standard weights to measure mass. Mass, length and time are called
physical quantities because they can be measured.

Unit

When we buy two kilograms of dal, the shopkeeper uses two ‘one kilogram’ weights
for the measurement. Thus, to measure two kilogram mass, we have to choose a
reference standard mass ‘one kilogram’. Two kilogram is twice of one kilogram.
Similarly, metre is the reference standard of length. Six metre is six times of 1 metre.
A unit is a reference standard quantity with respect to which the other quantities are
measured.

Measure the length of your desk with your palm. Ask your friend to do the same. Is the
length of the desk the same in each of the cases? You find that the length of your desk
is different for different people when it is measured with their palms.

For example, the length of the desk may be 12 times of your palm, or it may be 10
times of your friend’s palm.

Blooming Science & Environment Book 7 7

Nowadays, standard units like metre, kilogram,
second, litre, etc. are widely used to measure length,
mass, time and volume respectively. Hence, the unit
of measurement which is used by majority of people
in a region as a basic unit is called standard unit.

All the units are divided into two groups: fundamental Fig: Measuring of Length
unit and derived unit.

Fundamental Unit

The units of fundamental physical quantities like mass, length and time are called the
fundamental units. These units are independent of any other units. For example, the
unit of mass ‘kg’ cannot be expressed in terms of unit of length.

Derived Unit

The units of area, volume, velocity, etc. can be derived from the basic units of length
and time. Thus, they are called derived units. In other words, the units which are
derived from one or more of the fundamental units are called derived units.

Systems of Units

There are various systems of units to measure physical quantities. Out of them, the
main systems of units are given below.

MKS System

In MKS system, length is measured in metre, mass is measured in kilogram and time
is measured in second. It is also called metric system of units.

CGS System

It is known as the French system of units. In this system, length is measured in
centimeter, mass is measured in gram and time is measured in second.

FPS System

It is the British system of units. In this system, length is measured in foot, mass is
measured in pound and time is measured in second.

SI System

SI system is the improved and extended version of MKS system of units. In the
year 1960 A.D., the scientists in the ‘Eleventh General Conference on Weights and
Measures’ introduced this system. This system includes MKS system of units as well
as the units related to heat, light, electricity and magnetism. The following are the
seven fundamental quantities in the Sl system:

8 Blooming Science & Environment Book 7

The SI units of Fundamental Quantities SI Unit symbol
Metre (m)
Physical Quantities Kilogram (kg)
Length Second (s)
Mass Kelvin (K)
Time Ampere (A)
Temperature Candela (cd)
Current Mole (mol)
Luminous Intensity (brightness of light)
Amount of substance

Measurement of Lenght, Mass and Time

You have studied about measurement of length, mass and time in class 6 . The brief of
the measurement of these three physical quantities is given here for the recap.

Length

The distance between two points is called length. The length, breadth, height, thickness,
diameter, radius, depth, etc are example of length.

The SI units of length is metre (m). The length is measured by using appropriate types
of scale. The uses of scales depends upon their structures and length to be measured.

Metre scale rod 1 feet scale

Steel tape Fibre tape 50m/100m long tape

Fig: Various types of Scales Scan for practical experiment
The metric table of length is given below:

10 millimetre (mm) = 1 centimetre (cm)

10 centimrtre (cm) = 1 decimetre (dm)

10 metre (m) = 1 decametre (dam)

10 decimetre (dm) = 1 metre (m)

10 decametre (dam) = 1hectometre (hm) visit: csp.codes/c07e01

10 hectrometre (hm) = 1 kilometre (km)

Blooming Science & Environment Book 7 9

Mass 1 Kg 5 Kg

The amount of the matter contained in a
body is called its mass. The SI unit of mass
is kilogram(kg) and it is measured by using a
beam (physical) balance. A physical balance
is a device having two pans. The body whose
mass is to be measured is kept in one pan and
standard weights are kept in another pan. Now 250gm 1/2 Kg
a days, the digital balance with computerized
system are in use to make measurement convenient.

Triple beam balance General physical Digital display
balance balance

Fig: Devices used to measure mass

The metric table of mass is given below:

10 milligram (mg) = 1 centigram (cg)

10 centigram (cg) = 1 decigram (dg)

10 decigram (dm) = 1 gram (gm)

10 gram (gm) = 1 decagram (dag)

10 decagram ( dag) = 1 hectogram (hg)

10 hectogram (hg) = 1 kilogram(kg)

100 kilogram (kg) = 1 quintal (q)

10 quintal (q) = 1 ton (t)

Time
The interval between two events is called time. For example, when the sun lies at
zenith is one event and when the sun lies at zenith on next day is another event. The
interval between these two events is called as one solar day which is equal to 86400
seconds.


10 Blooming Science & Environment Book 7

The SI unit of time is second. The time is measured by using clocks or watches.

Fig: different types of clocks

The multiples and submultiples of second ae given below:
60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 days
365 days = 1 year

One second is defined as the 1 th of a solar day.
86400

1 day = 24×60×60 seconds
∴ 1 day = 86400 seconds.

Measurement of Area and Volume
Measurement of Area

Area is the space occupied by the surface of a body. Area is obtained by multiplying

two lengths. Therefore, the unit of area is square metre (m2) or square centimetre (cm2).

Area of a square having its sides 1 m each is equal to 1m2. Similarly, 1cm2 is the area

of a square of side 1cm. The area of a rectangular surface of length l and breadth b is

given by. By definition, we have
1m2 = 1m × 1m
Area of rectangular object (A) = l × b = 100cm × 100cm
= 10000cm2
Area of square = l2 = 104cm2

Area of circular surface = πr2
1
Area of triangular surface = 2 b × h

Similarly, area of a circular surface is

Area = π × (radius)2 or A = π r2

where, π = 22
7

Area of irregular plane

There are different objects around us which do not have fixed shape. For example,
a paper piece, a stone, a pepple a leaf, etc. They have irregular shape. The area of
irregular objects can not be caculated by using a formula. We can determinf the area of

an irregular surface by using a graph paper.

Blooming Science & Environment Book 7 11

Activity

To measure the area of an irregular surface

Materials required: A graph paper, pencil, irregular surface (a leaf)

Method: Draw the outline of the given irregular solid with a
sharp pencil on a graph paper as shown in figure. Count the
number of complete squares and incomplete squares within
the outline. Add half the number of incomplete squares to
the number of complete squares. These numbers of squares
give the approximate area of the irregular surface. If the
number of complete squares is x and number of half squares
is y and area of 1 square of the graph is 1cm2, then the area
is A = (x + y/2) × 1 cm2

Measurement of Volume

There are varieties of objects which are made up of matter. Matters exist in solid,
liquid and gas. The matter whether it is found in solid, liquid or gas occupies the space.
The space occupied by a body is called its volume. In SI system, its unit is cubic metre
(m3). In CGS system, its unit is cubic centimetre (cm3)

1 m3 = (1m)3 = (100cm)3 = 1000000 cm3 [1m = 100cm]

1 m3 = 106 cm3

Liquids such as petrol, diesel, water, etc are generally measured in litre (l). Millilitre
(ml) is the smaller unit. In one litre, there is 1000ml. One millilitre (ml) equals one
cubic centimetre (cm)3. Cm3 is also written as cc.

The volume of a rectangular body of length '1', breadth ' b' and height ' h' is given by

Volume = length × breadth × height

or V = l × b × h

By definition, we have

Volume of cuboids = l × b × h

1m3 = 1m × 1m × 1m

= 100cm × 100cm × 100cm

= 10,00,000cm3 = 106 cm3

1ml = 1cm3

1 litre = 1000ml = 1000cm3

Again, 1000 litre = 1000×1000 cm3 = 1000000 cm3 = 1 m3

1m3 = 1000 litre

Volume of cylinder = πr2h πd3
3
Volume of sphere = 4 πr3 or
3

12 Blooming Science & Environment Book 7

Measurement of Volume of Solid

Solid is one of the states of matter that has more or less fixed shape and occupies
the space. The space occupied by he solid is its volume. Then solid may be found in
regular or irregular in shape.

Volume of Regular Solid Match Box l

Some solid objects like a matchbox, a book, a ball, a cube, h
etc, have a regular shape. Thus, the objects with geometrical
shapes are called regular objects. The volume of such regular b
objects can be calculated by using the formulae.

The volume of a rectangular object is calculated by;

Volume = Length × Breadth × Height

i.e., V = l × b × h

Consider the following example:

Measure the length, breadth and height of a matchbox with a ruler. If 5cm, 3cm and
2cm are its length, breadth and height respectively, then its volume (V) will be given
by,

V = l×b×h

= 5cm × 3cm × 2cm

= 30 cm3

In a cube, its all sides are equal. So, the volume of a cube is given by the formula:

Volume of a cube (V) = (side)3

i.e. V = l3

For example, let each side of a cube has length 2 m. Its volume will be

V = l3

= (2m)3 = 8m3

Volume of an Irregular Solid Scan for practical experiment

There are many objects which have no regular shape. Such

objects are called irregular bodies. A stone, an iron nail, a piece

of glass, etc. are some examples of irregular shaped objects.

These objects have no accurate dimensions. Thus, the volume

of such objects can be determined by using liquid displacement

method. It means that the volume of the liquid is found out visit: csp.codes/c07e02
which the immersed solid displaces because the volume of the

solid is equal to the volume liquid displaces by that solid. This fact is used to find out

the volume of irregular solids by displacement method.

A measuring cylinder is used to find the volume of irregular solids Volume of an
irregular solid is measured by liquid-displacement method.

Blooming Science & Environment Book 7 13

Activity

To measure the volume of an irregular solid (a stone) by displacement method.

Material required: a measuring cylinder, string, water, a small sized stone

Method :

1. Take a measuring cylinder and String
fill it partially with water. Measuring cylinder

2. Read the level of the water on water
the scale graduated it. While
taking the reading of water level,
the eye should be kept straight
to the lower meniscus of the
water level as shown in the
figure.

3. Now, take a stone and tie it Stone
tightly to a string.

4. Lower it gently into the cylinder till it is completely immersed into the water
as shown in the figure.

Observation: The water level rises in the measuring cylinder. Note the water

level accurately.

Suppose,

Initial water level in the cylinder = x (before sinking the stone)

Final water level in the cylinder = y (after sinking the stone)

The volume of the stone = final water level - Initial water level

=y-x
Conclusion:
Scan for practical experiment

The difference between the readings of initial water level
and final water level gives the volume of the stone.

Precautions:

The following precautions should be taken while dropping
the stone in the cylinder:

a. The stone should be immersed in the cylinder gently visit: csp.codes/c07e03
using a thread. If it is dropped suddenly, either it may
break the cylinder or water of the cylinder may come out. In such situations,
the calculated volume of the stone is not correct.

b. The stone should be completely immersed into water.

c. The eye should be kept straight at the same level as the water so that lower
meniscus is focused.

14 Blooming Science & Environment Book 7

Note:
We cannot find the volume of common salt or sugar by this method because common
salt and sugar both dissolve in water. In such circumstances, you should replace
water by another liquid such as kerosene or spirit in which such substances do not
dissolve.

Measurement of Volume of Liquid

Volume of liquid is fixed but the shape is not fixed. Thus, when a liquid is poured
in different vessels, it takes the shape of those vessels. So, the volume of liquid is
measured in a measuring cylinder. They are found in different capacities such as 10ml,
15ml, 50ml, 250ml and 1000ml.

1000 ml 500 ml 250 ml 100 ml

The liquid which is to be measured is poured into the measuring cylinder and its level
is noted.

Volumetric Instruments

Various measuring vessels such as measuring cylinder, measuring can, pipette, burette,
volumetric flask, etc, are used to measure the volume of liquid.

Beaker Can Measuring cylinder Pipette Conical flask
Blooming Science & Environment Book 7 15

Activity

To measure the volume of water
Material required:
A measuring cylinder, a beaker, water
Method :
1. Take a measuring cylinder and gently pour water into

it
2. Observe the level of water carefully.

Observation : You will find that the level of water is not a plane but curved

such that the middle portion is more depressed than its sides.

Such a curved surface is called concave surface or lower

meniscus. While taking the reading of the water level, the eye

should be kept straight at the same level as the water so that

lower meniscus is focused. Note the level of the water in the

measuring cylinder.

Precautions : If the eye is kept above the water level, the volume of the water
seems higher and if the eye is kept lower than the water level,
the volume of the water seems lower than its actual value.

Result : The volume of the water as in the given figure is 82ml. Thus, we
should take a reading of water level by focusing the lower
meniscus.

Note: All liquids do not wet glass. Water, oil, kerosene, alcohol, spirit, etc. wet
glass. The liquids which wet glass form a concave surface in a glass vessel. For such
liquids, the water surface is more depressed in the middle than the sides. The eye
should be focused at the lower meniscus while measuring the volume of such liquids.

Mercury does not wet the glass surface. The liquids which do not wet glass surface
form a convex surface in a glass vessel. The mercury surface is more depressed at the
margin (sides) than in the middle. The eye should be focused at the upper meniscus
while measuring the volume of such liquids

Water Mercury .
16 Blooming Science & Environment Book 7

Volume of Gas
Gases have no fixed volume. It can be compressed to small volume. A large amount of
gas can be filled in a cylinder, volleyball, tube etc.
Measurement of Volume of Gas
Solids and liquids have fixed volume and they cannot be compressed. That is, their
volume can be changed considerably by applying external pressure on them. The
volume of any gas depends on the capacity of the container in which it is kept. Gas
does not have fixed volume and it can be compressed. For example, while pumping a
football, air is compressed inside it. More is the pressure of air, harder will be the ball.
So, the volume of air depends on pressure, which is exerted on it.

Activity

To measure the volume of air of a balloon.
Materials required: A measuring cylinder, a trough, an inflated balloon.
Method :
1. Take a trough and fill it partially with water and place bee-hive shelf in it.
2. Fill the measuring cylinder completely with water.
3. Covering its mouth with your palm, invert it over the bee-hive shelf in the
trough as shown in the figure.

h Air

Air bubbles

Balloon

4. Take the inflated balloon and open its mouth in the bee-hive shelf.
Observation: You will find that air bubbles move up in the cylinder
displacing water downwards. After a while, the air of the balloon
fills a part of upper portion of the cylinder. Note the water level
accurately.
Conclusion: This gives the volume of air in the balloon. The level h will be
volume of air

Blooming Science & Environment Book 7 17

Main Points to Remember

1. Measurement is important for the study of physics and in our day to day life.
2. Measurement is the comparison of an unknown quantity with a known
quantity.
3. A physical quantity is that which can be measured.
4. A unit is a reference standard quantity with respect to which we measure the
other quantities.
5. There are seven fundamental units in SI.
6. Standard units of mass, length and time are kilogram, metre and second
respectively.
7. Systems of units are FPS, CGS, MKS and SI.
8. The space occupied by a body is called volume.
9. One cubic metre is equal to 1000 litre.
10. Measuring cylinder, measuring can, pipette, burette, etc. are the volume
measuring devices.
11. The liquid which wets the glass surface form concave meniscus in a glass vessel.
12. The liquid like mercury which does not wet the glass surface forms convex
meniscus in a glass vessel.
13. Volume of a rectangular body is determined by using the formula:
Volume = length × breadth × height
14. The volume of irregular objects can be measured by displacement method.
15. Area of irregular surface is measured with the help of a graph paper.

PRO J ECTWORK

1. Find out the area and volume of your science book.

2. Measure the volume of your instrument box and your classroom and sleeping.

Exercises

1. Answer the following questions.
a. What is measurement?
b. Why is measurement important in our daily life? Explain.
c. What is a physical quantity?
d. Why should a physical quantity be measured?
e. Length of your pencil is 6 cm. what does it mean?

18 Blooming Science & Environment Book 7

f. Write short notes on different systems of units.
g. Define SI unit. Name seven fundamental quantities with their SI units.
h. How can we measure the area and volume of an irregular body?
i. Name volumetric instruments to measure volume of liquid.
2. Define the following.
Unit, Fundamental unit, Derived unit, Mass, Volume.

3. Solve the following numerical problems.
a. Change i. 300 cm into m. ii. 2000 cm2 into m2 iii. 312 mm into m.
iv. 2000 g into kg. v. 2 days into second. vi. 6h into second.
b. The length, breadth and height of a rectangular box are 24 cm, 6cm and 2cm
respectively. Find
i. the volume of the box.
ii. the area of largest surface of the box. [288cm3, 144cm2]
c. What is the area of a circle, if its radius is 3.5cm? [38.5cm2]
d. In the given figure, A is the level of water before introducing the solid and B is
that after introducing the solid. Find the volume of water and volume of the
solid.

e. Find the volume of given cylinder.

2 cm

15 cm

Blooming Science & Environment Book 7 19

4. Give reason.
a. Measurement plays an important role in our daily life.
b. The volume of an irregular object is found by using measuring cylinder.
c. CGS and MKS system of units are widely used.
d. The SI unit of time is second.
e. Same volume of cotton is lighter than same volume of iron.
5 . Distinguish between.
a. Fundamental and derived unit.
b. SI system and MKS system.

Glossary

Physical quantity : quantity which can be measured

Area : the space covered by a flat surface or piece of land

Measurement : Process of comparison of physical unknown quantity with a
certain standard quantity.

Standard : something known or widely established.

Unit : standard used to measure a physical quantity

Fundamental unit : independent unit

Derived unit : dependent unit

measuring cylinder : device used to measure liquid volume

Meter : SI unit of length

Kilogram : SI unit of mass

Second : SI unit of time

zenith : the point in the sky or celestial sphere directly above an observer

20 Blooming Science & Environment Book 7

2Chapter Force and Motion

Learning Outcomes

On the completion of this unit, students will be able to: Estimated Periods: 5+1
• define force and explain the types of force

• define distance and displacement.

• define friction and explain its effects.

• define speed and velocity and to expalin uniform and variable velocity.

• define acceleration

• solve simple numerical problems related to force, velocity and
acceleration.

Introduction

Force is required to do works. The force, push or pull generally causes displacement.
We do many activities in our daily life such as pushing and pulling the door, pulling
water from a well, stopping the moving ball, running and so on. All these activities
need force.

Force is used for carrying out various activities in everyday life.

We apply force while picking the glass of water, lifting the water from well, hitting
the ball, throwing a stone or anything. We do any act either pulling or pushing. So, to
move an object or to stop it from moving, it must be pushed or pulled.

The force is defined as an external agent that changes or tends to change the state of an
object from rest to motion or motion to rest. The gravitational force of the earth pulls
every object to the surface of the earth.

Effects of Force

Force has the following effects:

1. Force changes the state of a body

Your bag remains on the table unless somebody pulls
or pushes it. To move the bag, you have to apply force.
Likewise, if you roll a ball on the ground with a high speed,
it will not stop till any one disturbs it. Its speed gradually
decreases and finally comes to rest. The frictional force
acts on the ball to decrease its motion.

A body at motion comes to rest or a body at rest comes into motion only when the force
is applied to it.

Blooming Science & Environment Book 7 21

2. Force changes the shape and size of the body

When a spring or rubber is stretched, its length changes. If
you blow into a balloon or rubber ball, it changes in shape.
Likewise, ironsmith used his muscular force to hit the
red-hot iron with hammer and changes its shape.

3. Force changes the direction of a moving object

The baller throws the cricket ball with a huge velocity. The batsman
hits the ball with his bat. The ball changes its original direction. The
batsman applies the force to change the direction of motion of the ball.

4. Force changes the speed of moving object

A force applied in the direction of the moving objects increases its speed and a force
applied in a direction opposite to the motion of an object decreases its motion.



Unit of Force

Force is a physical quantity so it can be measured. The standard
unit of force is Newton (N). The force in which the earth attracts
an object of mass 1 kilogram is called 1 kilogram (1kg) force. One
kilogram force is equal to 9.8 Newton.

A spring balance is used to measure the force. It consists of a spring
. The force to be measured is applied at one end of the spring and
it’s another end is fixed somewhere. The force (weight) stretches the Spring balance
spring inside it. The measure of extension of the spring gives the
magnitude of the force.

Force is measured in the unit Newton (N), if mass is measured in Kilogram (kg) and
acceleration in metre per square second (m/s2). Then the force of any object of certain
mass can be calculated by using a formula, F = m × a.

1 N = 1kg × 1m/s2

∴ 1 N = 1 kg × m/s2

22 Blooming Science & Environment Book 7

Solved Numerical Problem

1. Calculate force applied on a body of mass 1500 kg if its acceleration is 2m/s2.

Solution:

Mass (m) = 500 kg

Acceleration (a) = 5 m/s2

Force (F) = ?

We know that,

F = m × a = 1500 × 5 = 7500N

Therefore, 7500 N of force is required to bring a van into rest.

Types of Force

We cannot do any work without force. We apply various kinds of force to do various
works. There are many types of force. Some of them are as follows:

1. Muscular Force

We use our body in various activities such as walking, playing,
riding a bicycle, kicking a ball, pushing a load, pulling the door
etc. Some animals such as oxen, donkey, horse are used to carry
the load and to plough the field. These animals use either pulling
or pushing force to do work. The force applied by the muscles of
the living-beings is called muscular force.

2. Pushing Force

The force that pushes or tends to push an object is pushing force.
Pushing a loaded cart, closing and opening the door, throwing a
stone, kicking a football etc. are examples of pushing force. The
force that pushes or tends to push an object is called pushing
force.

3. Pulling Force

Horse pulls a cart, Oxen ploughs the field. We pull bucket of
water from a well. These all are some examples of pulling
force. The force that pulls or tends to pull an object is called
pulling force.

4. Gravity and Gravitational Force

You know that the fruit falls on the ground from a tree. A tone
thrown upward returns to the ground. Water always flows down.
Atmosphere remains around the earth. These all are due to the
force of the earth, which attracts all the objects towards its
surface. The force of the earth that attracts the objects towards
its centre is its gravity.

Blooming Science & Environment Book 7 23

Similarly two objects in the universe attract each other by a force called gravitational
force.

The force with which the earth pulls an object towards its centre is called the gravity.
The force between any two heavenly bodies by which these are attracted with each

other is called gravitational force.

Moon
Sun Earth

5. Magnetic Force

If you bring a magnetic substance like pin, iron, iron dust and nail near a magnet, it

pulls these substances. It is because the magnet exerts some force on the magnetic

substances. If you bring near same poles of magnet together, they go away from each

other and bringing near opposite poles they attract to each others. It is due to some

force exerted by magnet. This is called magnetic force.

The force exerted by a magnet is called magnetic force. Scan for practical experiment

Activity

To demonstrate the magnetic force

Materials required : Two bar magnets, thread and stand.

Method : visit: csp.codes/c07e04

1. Suspend a bar magnet with a thread on a wooden stand.

2. Slowly bring another bar magnet with its north pole close to the north pole of
the suspended magnet as shown in the figure. Observe what happens?

3. Now, bring the south pole of the bar magnet towards north pole of the suspended

magnet. Observe what happens?

Repulsion Attraction

N N
S NS S SN

Observation : In first case, the north pole of a suspended magnet moves away. The
north pole of the suspended magnet moves towards the south pole of the bar magnet.
In second case, the north pole attracts with south pole of a bar magnet.
Conclusion : The repulsion between the like poles and attraction between the unlike
poles are due to the magnetic forces. It may be attractive or repulsive. This is the
law of magnet.

24 Blooming Science & Environment Book 7

6. Centripetal and Centrifugal Force

When a bus takes a turn in a bend, what do we experience?

Our body tends to move outwards from the centre of the curved
path. There is some force exerted to our body which pushes us
away from the centre. This is centrifugal force.

Have you ever ridden a bicycle on the curved path? Your body or bicycle bends towards
the centre of the curved path. There is some pulling force exerted to our body by a
curve path. This is centripetal force.

When a body moves in a circular path, it is acted upon by a force towards the centre of
the path called centripetal force. Another force which tends to move it away from the
centre is called centrifugal force.

When an object moves in a circular path, both the centripetal and centrifugal forces
work together. The centripetal and centrifugal forces both balance each other. These
forces are equal but act on opposite directions to each other. If centrifugal force is
greater than centripetal force, the object goes away from the centre. If centripetal force

is greater than centrifugal force, the object is pulled towards the centre.

Differences between Centrifugal Force and Centripetal Force

Centrifugal Force Centripetal Force

1. It is the force which pushes an object 1. It is the force which pulls an object
away from the centre. towards the centre.

2. Passengers in a turning bus move 2. The body of a cyclist in the curved
outwards from the centre. road bends towards the centre.

Activity

To demonstrate centripetal force
Materials required : A rubber ball and a piece of string.
Method:
1. Take a small rubber ball and tie it with a string of about 20cm long.
2. Hold the string tightly and rotate it.

3. Now, release the string and observe what happens?

Centrifugal force

Centripetal force

Observation: Until the string is held by hand, the rubber ball does not go away.
When the string is released, the ball goes away.
Conclusion : The centripetal force keeps the body to move in the circular path.

Blooming Science & Environment Book 7 25

Activity

To demonstrate centrifugal force
Materials required:
A small bucket, water and string.
Method:
1. Take a small bucket and tie it with a string.
2. Put some water in it.
3. Rotate it round and round.

Observation : The water in the bucket does not fall down or spill out.
Conclusion : The centrifugal force acting on water pushes it away.

7. Frictional Force

A ball rolling on the smooth surface travels over a longer distance before coming to
rest. But a ball rolling on the rough surface travels a short distance. It is because on the
rough surface a ball experiences a force, which opposed its motion.

The surface of an object is not perfectly smooth. There are some projections and
depressions on the surface of the object. When two solid objects are in contact with
each other, the projection of one fit into the depression of other and that interlock
between two objects. This interlocking between the surface opposes the motion and

the rolling object comes to rest. Scan for practical experiment

The force which opposes the motion of a body sliding on a
surface is called frictional force.

The frictional force depends upon-

(i) The roughness of the surface i.e. the nature of the two visit: csp.codes/c07e05
surfaces in contact: Friction is less on the smooth surface
and more on the rough surface. It increases with the increase in the roughness of
the surface.

(ii) Weight of the body: Friction depends upon the weight of the moving body. It is
more for heavier objects.

26 Blooming Science & Environment Book 7

8. Electrostatic Force

When a plastic comb or pen is rubbed with dry hair, it
can pick up small dirts or papers pieces kept nearer to it.
Similarly you might have seen lighting in the sky, sparks
while putting off woolen clothes, etc. All pen or comb
gains electrons from hair while rubbing and acquires
negative charge. When it is placed nearer to paper piece it
induces positive charge on paper piece and attracts. This
force of attraction due to charges is electrostatic force.

Electric charge is the physical property of matter that causes it to experience a
force. Electric charge is carried by subatomic particles names electrons and protons.
Electrons carry negative charge and protons carry positive charge.

Electrostatic force is the force that exist between electrically charged particles or
objects at rest. It involves the accumulation of charge on the surface of objects due to
rubbing.

Distance and Displacement

5

2

A1 B
3

4

Suppose a body is to move from a place A to another place B. There may be the number
of paths 1, 2, 3, 4, 5 etc. as shown in fig. To reach B from A, the length of the path
is different for different path. In the figure, path 5 is longest one. The length of path
followed by a body from one place to another is called distance covered by the body.

Rest and Motion
Things around us are either in motion or at rest. A flying bird, moving car, walking
people are some examples of moving objects. Similarly the trees, electric poles,
buildings, water in the container, standing boy are some examples of stationary objects.
To know whether an object is stationary or moving, we have to compare it with the
state of other objects around it. For example, a table lying in class is in the state of rest
because it does not change its position with respect to other objects lying in classroom.
An object is said to be at rest or stationary, if it is not changing its position with respect
to its surroundings.
While driving on the highway, you leave trees, electric poles, buildings, bridges and
people behind. In this case, you change your position with respect to those things you
leave behind.

Blooming Science & Environment Book 7 27

An object is said to be in motion, if it is changing its position with respect to its
surroundings.

Reference Point

It is the fixed point with respect to which the comparison is done. An object at rest does
not change its position with respect to a reference point.

Rest and Motion are Relative Terms

Suppose you are traveling in a car with your father. You are in a state of rest with
respect to your father. But you are in a state of motion with respect to the things outside
the car. You are leaving behind the buildings, trees, electric poles etc. Thus a body is
said to be either at rest or in motion only with respect to surrounding objects. They are
called relative terms because a body at rest, if changes its position it will be in motion.
Similarly, a body in motion changes its position to rest if there is a push or pull.

Uniform and Variable Motion

Motions are of two types. In terms of distance and time, they are uniform and variable.

Uniform Motion

A car is moving on a smooth road. Several positions of the car at every second interval
is shown below.

A car moves from a to b in one second and covers the distance of 5 metre. In the next
second, it further covers 5 metre and so on. The car covers equal distance in every
second from beginning to end. Thus, the car is said to be in uniform motion.

A body is said to be in uniform-motion, if it covers equal distance in an equal interval

of time.

0 sec 1 sec 2 sec 3 sec 4 sec

a 5m b 5m c 5m d 5m e

28 Blooming Science & Environment Book 7

Variable Motion

A car is moving on a heavy traffic road. Several positions of the car at every second
interval is shown below. A car covers 3 m in the first second and 10m in the second and
so on. The car covers unequal distance in each second from beginning to end. Thus, the
car is said to be in variable-motion.

A body is said to be in variable-motion, if it covers unequal distances in equal interval

of time.

In general, most objects have variable-motion. The motion of vehicles on a road, flow
of water in the river, walking of people on a foot path are all examples of variable

motion. 1 sec 2 sec 4 sec
0 sec

a 5m b 10m d 3m

Solved Numerical Problem

If a person takes 5 minutes to cover a distance of 1,000 m, what distances does the
person cover in a second?

Solution:

Here, Distance covered (d) = 1,000m

Time take (t) = 5min.

= (5 × 60) s

= 300s

Now, Distance covered in 300s = 1000m

Distance covered in 1 s = 1000 m
300

= 3.33m

Therefore, the person covers 3.33 metre in a second. His speed is 3.33 metre per second.

Speed

Speed of a body is the distance travelled by a body per unit time in any direction.

Blooming Science & Environment Book 7 29

The magnitude of speed is calculated by

Speed = total displacement =� d �
total time taken t

The SI unit of speed is metre per second and centimetre per second in CGS system.

Uniform and Non-uniform Speed

When a body travels equal distances in equal intervals of time, the body is said to be
moving with uniform-speed. If it does not cover equal distance in equal interval of
time, then the body is said to be moving in non-uniform speed. In such a case, average
speed is calculated rather than speed at every second. The average speed of the body
is calculated by a formula,

Average speed = total displacement
total time taken
If only two speeds are involved, then average speed = d1 + d2

t1 + t2
where d1 is the distance travelled in time t1 with the first speed and d2 is the distance
travelled in time t2 with the second speed.

Velocity

Speed and velocity are often used synonymously but in science they have different
meanings. Velocity is just speed in a particular direction.

Velocity is the distance travelled by a body in unit time in a particular direction.

The magnitude of velocity is calculated by the formula;

Velocity = displacement = s
time taken t

The SI unit of velocity is metre per second and cenitmetre per second in CGS system.

Unifrom Velocity

If a body covers equal distance in the same direction in equal interval of time, its
velocity is said to be uniform.

Variable Velocity

If a body covers different distances in unit time, such velocity is called variable

velocity. In such situation, average velocity is used, which is calculated by using the

formula given below.

Average velocity = Initial velocity+Final velocity
2
u+v
= 2



30 Blooming Science & Environment Book 7

or, It is also given as, Average velocity = Total displacement = s
Total time taken t

Vector and Scalar Quantities

Physical quantities are classified into two types. They are vector and scalar quantities.

Vector

Suppose a car is moving with a velocity of 50m/s from east to west. It means that
it covers 50 m in one second towards the west. Velocity have both magnitude and
direction. So, it is called a vector quantity. Similarly displacement, force, momentum
etc are vector quantities.
Vector is a physical quantity that has both magnitude and direction.
Scalar
Physical quantities like mass, temperature and speed have only magnitude but no
direction. Speed tells us distance covered by a body per unit time in any direction. It
means it is a scalar quantity.
Scalar is a physical quantity which has only magnitude but no direction.

Difference between Speed and Velocity

Speed Velocity

1.Speed is the distance covered by a 1. Velocity is a speed in a particular

moving body in any direction in a unit direction.

time. d
t
2.Speed = total displacement =� � 2.Velocity = displacement =� s �
total time taken time taken t

3. Speed is a scalar quantity. 3. Velocity is a vector quantity.

Relative Motion

The motion of everybody is relative, ie. the
motion of a body must be compared with
another object. This can be given in the
following example.

Let us consider two cars that move from a
point. Car A moves ten metre in 2 second.
Where as car B moves 12 metre in 2 second. The car A moves 10 metre and car B
moves 15 metre from a tree. Their relative motion is 10 m + 12 m = 22 m in 2 second
in the opposite direction.If they move in the same direction then their relative velocity
is 12 m - 10 m = 2 m in 2 second.

Blooming Science & Environment Book 7 31

Solved Numerical Problems

1. A man leaves home on a bicycle and reaches his office in 50 minutes.
His office is 10 km away from his home. Calculate the average speed of his
bicycle.

Here, Time (t) = 50 minutes

= (50 × 60)s

= 3000s

Distance (s) = 10 km

= 10 × 1,000m

= 10,000m

Average speed (v) = ?

According to the formula,

Speed = d
t

10,000

= 3,000

= 3.33 m/s
Therefore, the average speed of bicycle is 3.33 m/s.

2. If a school bus runs with a speed of 50 m/s, how far does it each in 8 minute?

Solution:

Here, Speed (u) = 50 m/s

Time (t) = 8 min.

= 8 × 60

= 480 s

Distance (s) = ?

According to the formula,
s
u = t

s =u×t

= 50 × 480

= 24,000m

= 24 km

Therefore, the school bus travels a distance of 24 km.

32 Blooming Science & Environment Book 7

Acceleration

Practically the velocity of a moving body is not uniform at every event. The velocity
of a body either increases or decreases. Whenever the velocity of a body increases, it
is said to have an acceleration.

The acceleration of a body is defined as the rate of change of velocity per unit time

Suppose a body is moving with an initial velocity u m/s and its velocity increases to
velocity m/s in t seconds. Then the increase in velocity in t second is (v - u) m/s.

Acceleration is calculated by using the formula given below.

Acceleration = Final velocity −Initial velocity = � v−u �
Time taken t

Symbolically, a = v−u
t
Unit

The SI unit of acceleration is metre per square second (m/s2)

If the increase in velocity is measured in m/s and the time in second, the acceleration
will be measured in metre per second per second. For example, the acceleration of a
bus 4m / s2 means in each second, the velocity of the bus increases by 4 m/s

If the velocity increases after every second, the acceleration is said to be positive. If the
velocity decreases after every second, the acceleration is said to be negative.

A negative acceleration is also known as retardation or deceleration.Retardation is the
rate of decrease in velocity.

Solved Numerical Problems

1. A bus starts to move form rest and acquires a velocity of 30 m/s in 10
seconds. Calculate its acceleration.

Solution:

Here, Initial Velocity (u) = 0m/s

Final velocity (v) = 30 m/s

Time (t) = 10 sec

Acceleration (a) = ?

We have,

a = v−u
t

= 30−u
10

= 3 m/s2

Therefore, the acceleration of bus is 3 m/s2.

Blooming Science & Environment Book 7 33

2. A car starts moving from the rest. If the acceleration of the car remains
4 m/s2 for 10 seconds, what will be its final velocity?

Solution;

Here, Initial velocity (u) = 0m/s

Time (t) = 10s

Acceleration (a) = 4 m/s2

Final velocity (v) = ?

We have,

a = v−u
t

or, v = u + at

= 0 + 4 × 10

= 40 m/s

Therefore, the final velocity of a car is 40 m/s.

Main Points to Remember

1. Force is defined as an external agency which changes or tends to change the state
of a body.

2. Types of force are as follows:

(i) Pulling force (ii) Pushing force

(iii) Centripetal force and centrifugal force (iv) Magnetic force

(v) Frictional force (vi) Gravitational force

3. The force which pulls or tries to pull an object is called pulling force.

The force which pushes or tries to push an object is called pushing force.

4. When a body moves in a circular path, a force acts towards the center, which is
called the centripetal force.

5. When a body moves in a circular path, a force acts outwards the center of the
circular path which is called centrifugal force.

6. The pull, which is exerted by a magnet on the magnetic substance like iron,
cobalt or nickel is called magnetic force.

7. The force with which the earth pulls the object toward it is called the force of
gravity.

34 Blooming Science & Environment Book 7

8. When a body moves or tries to move on the surface of another body, a kind of
force is created between the two bodies. This force is called frictional force.
9. The rate of change in position of a body is called speed.
10. The rate of change in position of a body in a particular direction is called velocity.
11. Physical quantities with only magnitude are called scalars. Physical quantities
with both magnitude and direction are called vectors.
12. The rate of change in velocity is called acceleration.
13. If a body covers equal distance in an equal interval of time, it is uniform velocity.
If a body covers unequal distance in an equal interval of time, it is variable
velocity.
14. Force is measured in the unit of Newton. The force exerted by the earth on an
object of mass 1 kg is 10N
15. Force is calculated by using the formula: F = m × a

PRO J ECTWORK

1. In an open area mark two points at 50 m and 25 m distance, take a stop
watch and run from first point to the next. Calculate the time required for you
to cover the distance of 100 m. Take a bicycle and measure the time to cover
the distance with a bicycle.

2. On a open ground mark two points at 50 m distance and find its centre. Tell
your two friends to run in a opposite direction from the central mark. Find the
relative motion of them by calculating velocity of each of them to the end mark.

Exercises

1. Fill in the blanks.
a. A..................................exerts force on iron, cobalt and nickel.
b. Force is measured in the unit of...................................
c. We are able to write because of...................................
d. ................on a body is produced by the gravitational force of attraction.
e. Wear and tear of a machinery is the result of...................................
f. Frictional force...............................as the weight of the sliding body increases.

Blooming Science & Environment Book 7 35

2. Match the following.

Column A Column B

Gravitational force kicking football

Frictional force cyclist on a curved path

Pushing force separation of mixture of iron

Magnetic force helps to walk

Unit of force falling of a fruit

Centripetal force Newton

3. Differentiate between the following.

a. Pushing and pulling force

b. Centripetal and Centrifugal force

c. Gravitational force and Frictional force

d. Speed and Velocity

e. Vectors and Scalars

4. Answer these questions.
a. What is force? Write its unit.
b. Name the five types of force
c. What is a pulling force?
d. What is a centripetal force?
e. What is a centrifugal force?
f. What is magnetic force?
g. What is a frictional force?
h. How is frictional force reduced in a machine?
i. What is the rest and motion? They are called relative terms, why?
j. What is the point of reference?
k. What is uniform velocity? What is relative velocity?
l. What is acceleration? Write its unit.
m. Explain the causes of friction between the two surfaces.
n. What are the effects of force? Explain.
o. Explain the nature of the frictional force.
p. How is friction useful to us?

36 Blooming Science & Environment Book 7

q. How is friction harmful to us?

r. Explain how the frictional force does not depend upon the surface area.

s. What kind of object is said to be stationary and what kind of object is said to
be moving?

t. Why is speed called a scalar quantity? Give reason.

u. Write down the difference between vector quantity and scalar quantity with
example.

v. What is a variable motion? Explain with an example.

w. If the velocity of a vehicle starting from rest reaches 5 m/s in 2 seconds, is the
velocity of the vehicle uniform? Explain.

5. Numerical Problems.

a. How much force is required to produce an acceleration of 40m/s2 on a body

of mass of 10 kg. (Ans: 400N)

b. If 30N force is required to lift a 5kg mass. Find the acceleration produced
by a body. (Ans: 6m/s2)

c. How much force is required to produce an acceleration of 42m/s2 on a car
of mass 1000 kg? (Ans:42000 N)

d. When a force of 30N is applied to a body of mass 2 kg, find the acceleration
produced on the body. (As: 15m/s2)

e. What will be the mass of body when 10N of force is applied on it so that it
produces an acceleration of 2m/s2? (Ans: 5kg)

f. On what amount of mass does 40N of force produces on acceleration of
2m/s2)? (Ans: 20kg)

g. Find the acceleration produced on a body of mass 15kg when 30N force
is applied on it. (Ans: 2m/s2)

h. Calculate the force required to produce an acceleration of 15m/s2 on a body
of mass 10 kg. (Ans: 150N)

i. When a force of 1500 N is applied on a body of mass 300 kg, find the

acceleration produced on the body (Ans: 5m/s2)

j. If a body is moving with an acceleration of 100m/s2 with the application of

force 750N, find the mass of the object. (Ans: 7.5 kg)

Blooming Science & Environment Book 7 37

Glossary

Rest : condition of not changing position.
Motion : condition of changing position.
Displacement : the shortest distance travelled by a body in a particular
direction.
Speed : the distance travelled by a body in unit time.
Velocity : the displacement made by a moving body in a unit time.
Uniform motion : a body covers equal distances in equal interval of time.
Scalar : quantity having only magnitude.
Vector : quantity having both magnitude and direction.
Relative velocity : the velocity of an object with respect to other object.
Static : Not moving
Agent : something that causes an effect.
Extension : expansion, enlargement
Projection : rising out to surface
Depression : reduction, lowering

38 Blooming Science & Environment Book 7

3Chapter Simple Machines

Learning Outcomes

On the completion of this unit, students will be able to: Estimated Periods: 3+1

• define simple machines.
• define and identify various types of simple machines like lever, pulley,

wheels and axle, inclined plane, wedge and screw.
• tell the uses of simple machines and to use them.

Introduction

We perform different types of works in our daily life. To do physical work we use
different types of machines, which make our works easier and faster. Mainly there
are two types of machines: simple and complicated. Tractor, the factory instruments
etc. are some examples of complicated machines but the other machines like dhiki,
sanaso, knife, sugar tongs etc. are simple machines. These machines are constructed
by the simple mechanism and so are called simple machines. In home, school, hospital,
college each and everywhere we use different kinds of simple machines, which make
our work easier and faster.

The simple devices and instruments which are used to make our work easier and faster
are called simple machines.

Uses of Simple Machine Scan for practical experiment

1. It makes work easier.

2. It can accelerate the work done.

3. It can change the direction of force.

4. It can be used to multiply the applied force. visit: csp.codes/c07e06
Effort and Load

The applied force at some point on a machine is called the effort. By application of
this force we do some work or spend some energy; this is called input energy or input
work. Taking this energy, machine applies the force in some other points; this force
does some work or spends some energy. This is called the output energy or output
work. The force that is to be overcome by the effort is called load.

Work done in the machine is called input work. Work done by the machine is called
output work.

Generally, output energy is less than the input energy because machine spends some
energy to overcome the friction, which produces heat and other forms of energy.

Blooming Science & Environment Book 7 39

However, in the ideal case or for the perfect machine we must have
Output energy = Input energy
Load x load distance = Effort × effort distance
This is called as principle of simple machine. The principle of simple machine states
that the output work is equal to input work provided there is no frictional force.

Classification of Simple Machines
On the basis of construction and function, simple machines are categorized into six
groups.
1. Lever 2. Wheel and axle 3. Pulley
4. Inclined plane 5. Screw 6. Wedge
Lever
Lever is a long rigid bar capable of moving about an axis
or a fixed point called fulcrum. The distance between the
fulcrum and the load is called the load arm and the distance
between the effort and the fulcrum is called the effort arm. The load arm and the effort
arm in the lever may or may not be equal. This relation is called principle of lever.
Principle of Lever
work done by the load = work done by the effort
load × load arm = effort × effort arm
On the basis of the location of effort, load and the fulcrum, lever are classified into
three groups. They are:
1.First class lever 2. Second class lever 3. Third class lever
First Class Lever
The lever in which, fulcrum lies at any point between load and effort is called first
class lever. First class lever shows all the properties of simple machines. It means
that it helps to multiply force, increase the rate of doing work, change the direction of
force and to make the work easier. Scissors, beam balance, see-saw, crowbar, handle of
water pump, tin shears, pliers etc are some examples of first class lever.

First Class Lever
40 Blooming Science & Environment Book 7

Second Class Lever

The lever in which, load lies at any point between the fulcrum and the effort is called
second class lever. In this lever effort arm is never shorter than the load arm so it helps
to multiply the applied force. Nutcracker, paper cutter, bottle opener, wheelbarrow,
opening and closing of door, lemon squeezer, etc are some examples of second-class

lever.

Effort Effort Load
Fulcurm

Load Fulcurm

Effort Second Class Lever

Third Class Lever

The lever in which, the effort lies at any point between load and fulcrum is called third
class lever. In this class of lever effort arm is always shorter than the load arm so it
accelerates work but does not multiply the effort. Sugar tongs, table knife, fishing rod,
broom, shovel, fire tongs, human forearm, stapler etc. are some examples of third class

lever.

Fulcurm Effort

Load

Effort

Third Class Lever

Wheel and Axle

Wheel and axle is a simple machine made up of two cylinders of different radii in
which both the cylinders spin on the same axis together. The cylinder of large radius is
called wheel and the cylinder of small radius is called axle. They are generally made
up of wood and metal. Both wheel and axle move together when the effort is applied.
Generally, effort is applied in the wheel and the load is attached to the axle as shown
in the fig. Door knobs, string roller of kit, steering of vehicle, screw driver, spanner,
wheel of sewing machine, windlass etc are some examples of wheel and axle. For
one complete rotation of the wheel and axle, the effort and load move through the

distance equal to the circumference of the wheel and axle respectively. It is also called

continous lever.

Blooming Science & Environment Book 7 41

Wheel Scan for practical experiment
Axle

Effort Load visit: csp.codes/c07e07

Pulley

A pulley is a circular disc that has a groove along the circumference over which a
rope of string can move. The pulley is adjusted in a frame having immovable axle.
When the disc moves, the axle does not move. In the pulley, load is connected to one
end of the rope and effort is applied on the other end as shown in the Fig. Pulleys are
generally made up of wood or metal. Pulley moves about an axis passing through
the centre. Pulley is fixed in the block. There are three types of pulleys: fixed pulley,

movable pulley and compound pulley.

Fixed Pulley

The pulley that does not move up and down while lifting the load Fixed pulley
is called the fixed pulley. This pulley is fixed on the support and
do not move with either load or effort. This pulley is considered as
the simple machine because they make the work easier and help
to change the direction of applied force. But it does not multiply
the applied force. Such pulley is used in wells, flags, cranes, etc.

Movable Pulley

The pulley that moves up and down while lifting the load is called the Movable pulley
movable pulley. This pulley magnifies the applied force. But this pulley
cannot change the direction of applied force since the load moves in the
direction of applied force (effort). The effort arm is always double of
load arm, so it magnifies the effort.

Compound Pulley

A combination of fixed and movable pulley is called compound
pulley. Since both types of pulleys are used, this pulley can multiply
force as well as change the direction of applied force. This type of
pulley system is also known as block and tackle. The cranes have
this kind of pulley.

Compound pulley

42 Blooming Science & Environment Book 7

Inclined Plane

It is difficult to walk in the steep road than in the inclined road. Similarly, it is easier
to push a heavy load in to the truck by using the object of sloppy surface rather than
to lift it vertically. This sloppy surface is called the inclined plane. Inclined plane is
a sloppy flat surface that joins a low level of land to the higher level. The inclined
plane is considered as the simple machine in the sense that it multiplies the effort and
accelerates the works. Effort is applied in the inclined plane along the longer distance,
which is equal to the length of the inclined plane, and the load is raised in the shorter
distance, which is equal to the height from the ground. In an inclined plane effort arm
is always longer than load arm.

E Scan for practical experiment

Ld h

visit: csp.codes/c07e08

Screw

Screw is a simple machine having a number of threads on
the cylindrical surface. A small groove is made on the top of
the screw with which screwdriver drives the screw into the
wood. The distance between the two consecutive threads is
called pitch. This is the distance moved by the screw in one
complete rotation. Jackscrew is an example of screw which
is used to lift the vehicle. Using the jackscrew, a person can
lift the vehicle of large mass. A jack screw of 10 kg will lift a mass of 1000 kg. Screw
nail, drill, etc are also examples of screw.

Wedge

The block having one flat end and other sharp end t
is called wedge. Knife, blade, axe etc are some l
examples of wedge. They are generally made up of
wood or steel. In the wedge, effort is applied in flat
end and sharp end moves inside the body.

Wedges are generally used to split the log of wood. Wedge
First a small gap is made in a wooden log with the

help of an axe. The wedge is put in the gap and hammered from the top then the wedge

moves into the log and splits it into two parts. They are considered as the simple

machine in the sense that, they multiply the effort and makes the work easier.

Blooming Science & Environment Book 7 43

Activity

Identify the given simple machine and write their names and uses by making a
table.

a. b. c. d.

e. f. g. h.

S.No Name of devices Type of simple machine Uses
a.
b.
c.
d.
e.
f.
g.

Main Points to Remember

1. The simple devices and instruments that are used to make our works easier and
faster are called simple machines.

2. Simple machines help to gain the speed on the works to change the direction of
force and to apply the force in the convenient point.

3. The work done on the machine is called the input work and the work done by the
machine is called the output work.
4. The principle of simple machine states that the output work is equal to the input
work provided there is no frictional force.
5. There are six types of simple machines: lever, wheel and axle, screw, inclined
plane, wedge and pulley.
6. Lever is a long rigid bar, which is capable of moving in a fixed axis or point called
fulcrum.
7. There are three types of levers: first class, second class and third class lever.

44 Blooming Science & Environment Book 7

8. Wheel and axle is a simple machine having two co-axial cylinders, large
cylinder is called the wheel and the smaller cylinder is called axle.
9. Pulley is a circular disc that moves in a fixed axis.
10. Inclined plane is a slanted flat surface that connects lower level of land to the
higher level.
11. Screw is a simple machine having thread in the cylindrical surface.
12. Wedge is a block having one sharp edge and other flat edge.

PRO J ECTWORK

1. Collect the different types of devices used in your daily life and find
whether they are simple machines or not. Classify them. Draw their diagram
as well.(any five)

2. Make a pulley system by using some materials available in your locality and
demonstrate it in your class.

Exercises

1. Fill in the blanks.
a. In .................................. class lever load lies between effort and fulcrum.
b. Pulley changes the..................................of force.
c. The small cylinder of wheel and axle is called...................................
d. Knife is an example of...................................
e. The road on a hilly region is an example of...................................
2 State whether the following statements are true or false.
a. All simple machines increase the force applied.
b. Handle of water pump is an example of inclined plane.
c. More effort is needed to lift a load in a single fixed pulley.
d. Sharp tools are examples of wedge.
e. A person can lift a car easily, if he uses a jack screw.
3. Write the class of lever shown in the figure below.

Blooming Science & Environment Book 7 45

4. Answer these questions.
a. What is a simple machine? Write its advantages.
b. What is lever? Give two examples of it. What is principle of lever?
c. What is wedge? Give two examples
d. In which class of lever is the effort arm always smaller than the load arm?
e. What is screw? Give examples.
f. What is wheel and axle? Give examples.
g. What is an inclined plane? Give examples.
h. What is a pulley? What is its function?
i. Draw the diagrams of three classes of levers showing the position of the load,
effort and fulcrum in order.
j. Draw a diagram of single fixed pulley.
k. Mention various types of simple machines used in your home and classify
them according to their structure and uses.
l. Wheel and axle is called continous lever, why?
5. Give reasons for.
a. Iron cutting scissors have short cutting edges whereas cloth cutting scissors
have long edges.
b. It is easy to open the lid of a can by using a spoon.
c. The road on the hilly region is made longer with several bends.
d. Second class lever is widely useful.
e. Inclined plane is also called second class lever.
6. Classify the given simple machine into different groups.
Kite roller, dhiki (husker), see saw, screwjack, axe, knife, ladder, hilly road, bottle
opener, wheel used to pull curtain.

Glossary

Simple machine : a device which makes our work easier, faster and more
convenient.
Lever : a rigid bar that is free to rotate about a fixed point called
fulcrum.
Wheel and axle : simple machine consists two co-axial cylinders of
different diameters and mounted on an axle.
Pulley : a sloping or inlcined surface used to roll loads to higher
level.
Screw : a device like a nail used to fasten things which has
grooves on it called threads.
Wedge : a device consisting of two inclined planes placed back
to back.
Mechanical advantage : ratio of load to the effort.

46 Blooming Science & Environment Book 7

4Chapter Pressure

Learning Outcomes

On the completion of this unit, students will be able to: Estimated Periods: 3+1

• define pressure and establish the relationship of pressure with force and

area.
• tell utility and application of pressure in daily life.

Pressure

Put a piece of foam on a table and place a brick on it from its flat surface. Observe
compression of the foam. Again place the same brick from its narrow surface on the
foam. Observe the compressing of foam.

What do you find?

You will find that foam was compressed less in
first case and more in the second case. Why?

In the first case, surface area occupied by the
brick is more than that in the second case. Brick Less area exerts more pressure
exerts more force in second case even though
weight of brick is same in both cases. It shows that pressure in second case is more
than that in the first case.

Pressure is defined as the force applied of a body per unit area.

Pressure is calculated by using the following formula;

Pressure = Force
Area

P= P
A

Where, F is applied force and A is surface area covered by an object. P is pressure and
it is measured in Pascal(N/m2).

The SI unit of pressure is Pascal (Pa). One Pascal pressure is defined as that pressure
in which one Newton force is acted per square metre area.

1 Pa = 1N
1m2

∴ 1 Pa = 1N/m2

Blooming Science & Environment Book 7 47

Experimentally, it is found that pressure is directly proportional to the applied force
and inversely proportional to the area on which the force is acting normally.
i.e. P � F...........................(i)

P� 1 ........................... (ii)
A
F F
Combining equation (i) and (ii) we get, P � A or, P = k A Scan for practical experiment

where, k is a constant.

If, F = 1 N, A = 1m2 and P = 1 Pa, then k = 1

Therefore, P = F
A

Application of Pressure visit: csp.codes/c07e10

It is easier to cut things by using a sharp instrument than a blunt ones, why? The
foundation of a building is made wider than its walls. What may be the reason behind
it? The both examples given above are related to the pressure. In the first case, the
sharp instrument has less area, which exerts more pressure. In the second case, the area
of the foundation is increased to reduce the pressure exerted by the walls. The above
examples also show that area is the main factor which can alter the magnitude of
applied force to do different types of works.

Due to this, we can say a girl with pointed-heeled shoes
would make a deeper impression on clay than an elephant
applying a larger force on a comparatively larger area,
because the girl is exerting force on a smaller area. So,
the pressure exerted by the girl is more than the pressure
exerted by the elephant, although the girl has a lot less weight than the elephant.

Some applications of pressure in everyday life are listed below:

F It is easier to cut by using a sharp knife because of the small area of its cutting
edge. Even a small force creats a large pressure on the surface being cut.

F A pointed needle goes through cloth, cardboard and even skin because the sharp
point is applied to a very small area, compared to the total force applied.

F Heavy trucks are fitted 6 or 8 wheels. This arrangement increases the area of
contact and hence reduces the pressure on the ground at each wheel.

F Desert animals like camels walk easily on the sand as compared with most other
animals because they have broad feet.

F The foundation of high buildings are made wide, so that they exert less pressure
on the ground and therefore do not sink.

F Tractors ploughing fields have large and wide rear wheels so that they don't sink
deeper in mud.

48 Blooming Science & Environment Book 7

Solved Numerical Problems

1. The weight of a book is 5N and it covers an area of 0.2m2. Find the pressure
exerted by the book.

Solution:

Here,

F
P= A

5
= 0.5

= 25Pascal.

2. A boy weighting 50 kg stands on an ice skate, the blade of which is 0.5 cm wide
and 25 cm long. What pressure does he exert?

Solution:
Here,
Force due to the boy is his weight Force (F) = 50 kg wt
= 50 × 9.8 N
= 490 N

Area over which the force exert (A) = l × b

= 25 × 0.5

= 12.5 m2
10 ×100

= 125 m2
10000

= 12.5 cm2
Now, using the formula

P = F
A

= 490×1000
125

= 392000

So, the pressure exerted by the boy is 392000 Pa.

Blooming Science & Environment Book 7 49

3. An atmosphere pressure of 1.1 × 105 N/m2 acts on a wall of structure area 15m2
find the force acting on the wall.

Solution:

Pressure (P) = 1.1 × 105 N/m2

Area = 15 m2

We have P = F
A

F =P×A

= 1.1 × 105 × 15

= 16.5 × 105 N

4. The weight of a lady exerts a force of 800 N. She stands on one foot and the heel
of her shoe occupies 1 cm2. What pressure does her shoe exert?

Solution:

Force exerted by weight of the lady (F) = 800 N

Area occupied by the heel of her shoe (A) = 1cm2

= 1
10, 000m2
F
P = A

P = 800 × 10,000

= 8,000,000 N/m2

= 8 × 106 Pa

Atmospheric Pressure

The earth can be imagined as a ball in the ocean of air. The surrounding of air on the
earth is called atmosphere. The air present in the atmosphere is also a matter; therefore
it has its weight. Due to its weight the air presses the earth and all the bodies on its
surface. The pressure given by the weight of the air present in the atmosphere is called
atmospheric pressure. Atmospheric pressure alters with increasing height from sea-
level, the pressure is 760 mm Hg (millimeter mercury). The instrument used to measure
atmospheric pressure is called barometer. It is of two types: mercury barometer and
aneroid barometer. A mercury barometer contains mercury but an aneroid barometer
does not contain any liquid in it.

50 Blooming Science & Environment Book 7