HPE-book-7-final-for-press

KEDC Approved by Government of Nepal, Ministry of Education,
Curriculum Development Centre, Sanothimi, Bhaktapur

KEDC's

Science and Environment

7Book

Writer
Kishor Nepal

M.Sc., M.A., B.Ed.

Kantipur Education Development Council

Maharajgunj, Chakrapath, Kathmandu, Nepal
Phone: 4720202/2151710
Email: [email protected]
Website: www.kedcnepal.com

KEDC

Kantipur Education Development Council
Maharajgunj, Chakrapath, Kathmandu, Nepal
Phone: 4202027/2151710
Email: [email protected]
Website: www.kedcnepal.com
Kantipur Education Development Council 2058 ALL
RIGHTS RESERVED. No part of this book may be
reproduced or transmitted in any form by any means,
electronic or mechanical, including photocopying and
recording, or by any information storage and retrieval
system, except as may be expressly permitted in writing
by the publisher.

Written by:
Kishor Nepal

Contributor:
Ghanashyam Dhakal

Edition:
First, 2018

Layout/Design
Sarika Koirala

Illustrator:
Umesh Chandra Adhikari

Preface

Science is a fascinating subject which is widely spread in the world
we live in, as it focuses on the cause and effect, besides the reasons.
Science becomes fun and interesting to a student when it is taught in an
interactive manner and is related to his/her surroundings.

The early schooling years in a student's life is of extreme importance.
These are the times when they focus their eyes and mind on everything
that is new and appealing. Their attention span is short and they require
constant reinforcement and what interests them the most is things and
events around them. This is the golden opportunity to inculcate in them
a spirit of adventure and inquiry, to teach them to ask, to reason and to
pick up healthy habits.

With this in mind, KEDC decided to bring out a science series for the
junior classes which would be simple to read and still convey the idea
of scientific discovery to the students. Moreover, an effort was made to
make the book extensively illustrative. Most of the concept is presented
and demonstrated by simple experiments which the teacher can help
the students to perform on their own. This series also addresses the
objectives of the present curriculum, appropriately planning and
fulfilling the needs of students and teachers.

We sincerely hope that this series would prove to be an interesting
experience for students. Any suggestions for further improvement will
be welcomed.

Contents 1
17
1. Measurement 33
2. Force and Motion 48
3. Simple Machine 56
4. Pressure 71
5. Work, Energy and Power 87
6. Heat 98
7. Light 109
8. Sound 119
9. Magnet 130
10. Electricity 150
11. Matter 166
12. Mixture and Solution 174
13. Metals and Non-Metals 181
14. Some Useful Chemicals 192
15. Vertebrates 211
16. Plant Life 224
17. Cells 238
18. Life Process 246
19. Rocks and Minerals 260
20. Weather and Climate 275
21. The Earth and Space 294
22. Environment and Its Balance 313
23. Environment Degradation and Its Conservation
24. Environment and Sustainable Development

1Lesson Science

Measurement

Specific After the completion of the lesson, students will be able to:
Objectives
• introduce measurement and tell its importance.
• develop basic manipulative skills related to measurement.
• introduce SI system of measurement and its uses.
• define length, mass, time, area and volume with their SI units.
• calculate the surface area of regular and irregular objects.
• explain the method for measuring the volume of liquids and irregular objects.
• solve the general numerical problems related to area and volume.

Preliminary Syllabus
Concept • SI unit

Measurement is one of the best tools which a scientist has. It plays • Length and its units
a vital role in physics. It is sometimes known as an exact science.
Many great researches as well as discoveries in science have only • Mass and its units
been possible due to accurate measurement. Measurement is an
integral part of human race. Without it, there will be no trade, • Time and its units
no statistics. Even we can see the philosophy of measurement in
little kids who don't even know what measurement is. Kids try to • Area
compare their height, size of candy, size of dolls and amount of
toys they have. All these happen even before they know about • Regular and
measurement. Thus, measurement plays vital role in day-to-day Irregular object
life. Moreover, very accurate and precise measurements are
required for the advancement of science. We have been able • Area of regular and
to send satellites and even men on the moon which was possible irregular surface
because of the exact knowledge of length and time, which we
have obtained by defining some standard units of measurement of • Volume of solid and
mass, length and time. liquid.

Besides, we perform different activities in our day-to-day life.
So, we come across various situations where we have to measure
something. Sometimes we need to measure the mass, length, volume,
time or the temperature of an object. We use various devices and
equipments to measure different physical quantities.

Science and Environment Book - 7 1

Introduction

Measurement is the comparison of unknown physical quantity with a known
standard quantity of the same kind. It is the determination or estimation of
ratios of quantities. It is the process in which the unknown physical quantities
are determined by the help of a known physical quantity. We use various
scientifically advanced machines and equipments to measure different
quantities but such was not the case years ago. People didn't have advanced
equipments for measurement. They used some traditional methods for
measurement in their daily life. They used their hands and fingers to measure
the length. They used mana and pathi to measure the quantity of the grains.
These kinds of measurement are not uniform in all places. It varies according
to place and even among the individuals. So, there was necessity of a change
in order to maintain the uniformity in measurement throughout the world. To
fulfill this necessity, a new system of measurement was introduced which is
known as SI system.

SI system

The 12th General Conference of Weight and Measurement held at France in
October 1960 made an agreement to use international system of unit to bring
uniformity in the measurement. This system of measurement is known as
SI system which stands for System de International Unit in French. It is an
internationally accepted system and have the same value all over the world.

Some of the fundamental physical quantities and their units in SI system are
given below.

Measurement SI units Symbol
Length Metre m
Mass Kilogram kg
Time Second s
Temperature Kelvin K
Electric current Ampere A
Luminous intensity Candela cd
Amount of substance Mole mol

2 Science and Environment Book - 7

These fundamental units are considered as the standard units of measurement
as they are accepted and applied all over the world. 1 metre of length denotes
the same length all over the world and 1 kg mass means the same mass
everywhere. They have the uniform value throughout the world.

Length and its measurement

Length refers to the distance

between two points. Height,

breadth, thickness, diameter,

radius, etc. are also the forms

of the length. For example: the

distance between the base of

your foot and the top of your Scale Measuring tape
head is the length of your body

or is your height. Similarly, the distance between one end of your desk to the

other end is the length of your desk.

We use various equipments for the measurement of the length like scale, metre
rod, measuring tape, etc. The type of equipment to be used depends upon the
length of the object. The length of a short object is measured by a small scale,
clothes are measured by a metre scale and the length of the field and the roads
are measured by a long measuring tape.

Unit of length

The SI unit of length is metre. Some common standard units of length are inch,
millimetre, centimetre and kilometre. Depending on the size of the object, that
is to be measured, we have to choose an appropriate unit.

For example, we use the unit metre to measure the length of piece of a cloth,
kilometres to measure the distance from one place to another, millimetre to
measure the thickness of the hair, and so on. Centimetre (cm) and millimetre
(mm) are used to measure shorter distance while kilometre (km) is used to
measure longer distance.

One kilometre is divided into 1000 equal divisions, each called metre. One
metre is divided into 100 equal divisions, each called centimetre which is again
divided into 10 equal divisions each division is called millimetre. Observe the
table to know how to convert one standard unit to another.

Science and Environment Book - 7 3

10 millimeter (mm) 1 centimetre (cm)
10 centimetre (cm) 1 decimetre (dm)
10 decimetre 1 metre
10 metre 1 decametre
10 decametre 1 hectometre
10 hectometre 1 kilometre

A unit can be converted to another. Here is an example.

Example 1: Saru and her friend Saroj live 4000 m away from each other. Express
the distance between their houses in kilometre (km).

Solution: We know that 1000 m = 1km

1 m = 1 km
1000

4000m = 1 × 4000 km = 4 km
1000

Therefore, 4000 m = 4 km

Therefore, the distance between the two houses is 4 km.
Ways to take accurate measurement of length

1. We should place our eyes vertically above the point where the measurement
is to be taken or if in case you are measuring a vertically standing object
you have to keep your eyes horizontally straight to the point to be noted.

2. We should place the scale exactly along the length to be measured.

4 Science and Environment Book - 7

3. If the starting point of the scale is broken, we should not start measurement
from the broken part but the nearest whole number mark should be used
as a starting point. In this case, the difference of the reading at the two ends
will give the length of the object.

Activity 1

Measure the length of different objects listed below and convert them into
different units too.

Objects millimetre centimetre metre
Length of your pencil
Length of your desk
Height of your friend

Measurement of the diameter of a spherical object

The diameter of spherical objects like football, volleyball, cricket ball, etc.
cannot be directly measured with a scale. So, a different method is applied
to measure their diameter. First of all, you need to place the ball on a smooth
surface. Now put two solid blocks on either side of the ball as shown in the
diagram. Then, measure the distance between the two blocks by using a scale.
The reading that you get is the diameter of the ball.

Science and Environment Book - 7 5

Activity 2

Take a volleyball and a tennis ball. Find the difference between their
diameter.

Mass and its measurement

The total amount of matter

contained in a body is called

its mass. The SI unit of mass

is kilogram. Mass and weight

of an object are often used

interchangeably but they are

not exactly same. Unlike weight, Beam balance Grocers balance
mass of an object remains

same everywhere whether you

measure it on earth or the moon. 1kg sugar contains same amount of matter

whether it is on earth or taken to the moon.

A physical balance or a beam balance is used to measure the mass of an object.
A beam balance consists of two identical plates placed at equal distance from a
rigid bar. A known standard mass is kept in one plate and the substance whose
mass is to be determined is placed on the other plate until the plates stay in a
equilibrium position.

We can also find digital weighing balance these days which are easier to use.

Unit of mass

The SI unit of mass is kilogram. There are multiples and submultiples of
kilogram too. While measuring the smaller masses of substances like gold,
silver etc we use gram (g) and milligram (mg). These are sub- multiples of
kilogram (kg). Similarly, the large amount of the substances are measured in
quintals and tons. The various units of mass are given below.

1000 milligram (mg) 1 gram (g)

1000 gram (g) 1 kilogram (kg)
100 kg 1 quintal

10 quintal 1 tonne

6 Science and Environment Book - 7

Activity 3

Measure the mass of different objects like book, pen, instrument box,
dusters, etc. using a physical balance and note their weight in terms of kg.

Time and its measurement

The duration or interval between two successive events is known as time.
Time is a fundamental quantity which usually indicates duration i.e. period
or interval. The SI unit of time is second (s). We also measure time in minute,
hour, day, week, month, year, decade, millennium etc. Short duration of time
is measured even in millisecond, microsecond, nanosecond, etc. The multiples
and sub-multiples of time are given below.

60 seconds 1 minute 365 days 1 year
60 minutes 1 hour 12 months 1 year
24 hours 1 day 10 years 1 decade
7 days 1 week 100 years 1 century
30 days 1 month 1000 years 1 millennium

Time is measured by using a clock. There are different types of clock like
pendulum clock, electronic clock, digital clock, wrist watches, etc. We use stop
watch to measure small interval of time.

Regular and irregular objects

We find objects of different shape and size in our surrounding. Some of them
have a fixed geometrical shape but some of them do not. The objects which
have a fixed geometrical shape and a proper dimension are known as regular
objects. For example, a football has a spherical shape, a coin has circular shape,
a geometrical box has cuboidal shape. Similarly, book, pen, chalk, brick, etc.
are also regular objects.

Book Football Pen Chalk
Science and Environment Book - 7 7

The objects which do not have a definite geometrical shape and proper
dimension are called irregular objects. Pieces of stone, paper and leaf are some
examples of irregular objects.

Stone Leaf Broken glass

Area

The region occupied by the plane surface of an object is called area. Its SI unit
is square metre (m2). It can also be measured in terms of mm2, cm2, km2, etc.

Measurement of area of regular objects

The area of regular objects can be easily measured by using their respective
formula.

1. Area of a rectangle

Area (A) = length (l) × breadth (b) breadth (b)
\A=l×b
length (l)
2. Area of square (A) = length (l) × length (l)

A=l×l

\ A = l2 r length (l)
3. Area of a circle (A) = p × (radius)2

\ A = pr2

Now, let's see some examples to illustrate the concept of previously
mentioned terms and formulae.

8 Science and Environment Book - 7

Solved Numerical Problems

Example 1 : Find the area of a rectangle having length and breadth 6 m and
4 m respectively.

Solution:

Length of a rectangle (l) = 6 m
Breadth of a rectangle (b) = 4 m
Area of a rectangle (A) = ?
We know,
Area of a rectangle (A) = length (l) × breadth (b)
=6×4
= 24 m2
Hence, the area of the rectangle is 24 m2.

Example 2 : Find the area of a circle with 7 cm radius.

Solution:

Radius of the circle (r) = 7 cm

Area of circle (A) =?

We know,

Area of circle (A) = p × (radius)2

= 22 × (7)2
7

= 22 × 72
7

= 154 cm2

Hence, the area of the circle is 154 cm2.

Measurement of area of irregular objects

It is not possible to measure the area of the irregular objects using the formulae
as of the regular object because they do not have a fixed geometrical shape. But
we can measure the area of these objects by a graphical method.

In this method, an irregular, object for example, a leaf is placed over a graph
paper and its outline is traced by using a pencil. Now the leaf is removed

Science and Environment Book - 7 9

and the number of complete square within the
outline are counted first. Let the number of
the complete squares be a. Then the number
of incomplete square which are half or more
than half within the outline are counted. Let the
number of incomplete square be b. The other
small squares are neglected. Now, the total
number of squares (a + b) are multiplied by the
area of one square in the graph paper. In this
way, the area of an irregular object is calculated.

Volume

The total space occupied by an object is called its volume. Its SI unit is cubic
metre (m3). Volume can also be measured in terms of mm3 and cm3 but the
units like ml and litre are in more practice.

1000 cm3 = 1 litre.

Measurement of volume of regular objects

The volume of regular objects can be measured by using their respective
formula.

1. Volume of a cuboid (V) = length (l) × breadth (b) × height (h)

\V=l×b×h h
b
2. Volume of a cube (V) = (length)3 l

\ V = l3 r

3. Volume of a sphere (V) = 4p radius3
3
\V = 4 pr3 r

3
4. Volume of a cylinder (V) = p (radius)2 × height

\V = pr2h h

Let's relate the above formulae with numerical problems.

10 Science and Environment Book - 7

Solved Numerical Problem

Example 3: Find the volume of a cylinder with radius 14cm and height 30cm.

Solution:

Radius of cylinder (r) = 14 cm.
Height of cylinder (h) = 30 cm
Volume of a cylinder (V) = ?

We know
Volume of cylinder (V) = p (radius)2 × height
= 22 × (14)2 × 30

7
= 9240 cm3
So, the volume of the cylinder is 9240 cm3.

Measurement of volume of liquid

Liquid does not have its own shape but it definitely occupies volume. It takes
the shape of the vessel where it is kept in. So, its volume can be measured by
keeping it in a measuring vessel such as measuring cylinder, conical flask,
pipette, burette, etc.

The standard unit of volume is cubic metre (m3). The volume of the small
bodies can be measured in a unit smaller than the cubic metre such as cubic
centimetre (cm3) and cubic millimetre (mm3). In general practice, the volume
of the liquid is measured in litre (l). The smaller unit of litre is millilitre (ml)
which is equal to one cubic centimetre (cm3). The cubic centimetre is also
written as cc. Hence 'cc' and 'ml' means the same. The conversion of litre into
cubic metre is given below:

1 ml = 1cm3
1l = 1000 cm3
\ 1m3 = 1000l

To measure the volume of a liquid

The liquid is poured into a measuring cylinder. Now, the reading of the
measuring cylinder at the surface of the liquid is noted. You need to keep your
eyes straight to the level of liquid while taking the reading. The reading in the
measuring cylinder is the volume of the liquid.

Science and Environment Book - 7 11

All the liquids do not make up

same type of surface in the vessel.

The liquids like water, alcohol, concave convex
oil, kerosene wet the wall of the meniscus meniscus
vessel and thus form a concave water mercury

surface which is called concave

meniscus. So, we need to take Concave and convex measures
the reading of lower meniscus in

these type of liquids. Similarly, the liquid like mercury does not wet the wall of

the vessel and thus forms a convex surface in the vessel which is called convex

meniscus. So, we take the reading of its upper meniscus while measuring its

volume.

The shape of the liquid surface in which the centre is depressed more than the
sides is called concave meniscus. Similarly, the shape of liquid surface in which
the centre is raised and the sides are depressed is called convex meniscus.

Measurement of volume of irregular solid objects

The volume of irregular solid objects like stone, piece of brick and glass can
be determined by using a measuring cylinder applying water displacement
method.

Activity 4

To measure the volume of a stone. y

Materials required: Measuring cylinder, water, x
thread, piece of stone.

Procedures:

1. Keep some water into measuring cylinder
such that piece of stone can be completely
immersed in water but water should not
completely fill the measuring cylinder.

2. Note down the initial level of water in a
measuring cylinder. Let it be x.

12 Science and Environment Book - 7

3. Tie the stone with a thread and immerse it completely into the measuring
cylinder as shown in the figure. The level of water rises up.

4. Now, note the final level of water in the measuring cylinder. Let it be y.
Observation:
Initial level of water = x, final level of water = y
The, volume of the stone is given by (V) = (y - x) cm3
Conclusion:
The volume of water displaced is the volume of the irregular object i.e.
stone.

Points to remember

1. Measurement is the process of determining the unknown physical
quantity with the help of known physical quantity.

2. SI system is introduced to bring the uniformity in measurement
throughout the world.

3. The distance between any two fixed points is called length. Its SI unit
is metre.

4. The total matter contained in a body is called mass. Its SI unit is kg.
5. The duration or interval between two events is called time. Its SI unit

is second.
6. Objects having definite geometrical shape are called irregular objects.
7. The total space occupied by a plain surface of an object is called area.

Its SI unit is m2.
8. The total space occupied by an object is called volume. Its SI unit is

m3.
9. Volume of irregular solids is determined by using a measuring

cylinder.
10. Volume of liquid is measured by using measuring cylinder.

Science and Environment Book - 7 13

Exercise

1. Choose the best answer from the given alternatives:

a. Which of the following is not unit of length?

i. metre ii. kelometre iii. mile iv. pound

b. The SI unit of temperature is

i. Celsius ii. Kelvin iii. Fahrenheit iv. Ampere

c. What is the SI unit of area?

i. m ii. cm2 iii. cm3 iv. m2

d. The space occupied by the surface of an object is called________.

i. perimeter ii. area iii. volume iv. density

e. Which of the following is not true?

i. 1000 ml = 1l ii. 1000 cc = 1l

iii. 1000 ml = 1cc iv. 1ml = 1cc

f. The volume of a spherical object can be determined by the formula

i. l × b × h ii. l3 iii. pr2h iv. 22 pr3
2. Fill in the blanks with correct words. 7

a. In SI system, amount of substance is measured in _______.

b. _______ is the SI unit of electric current.

c. The distance between any two fixed point is called _______ .

d. Cubic metre is the SI unit of _______.

e. Objects which do not have fixed geometrical shape are called _____ .

f. Volume of irregular objects can be measured by water _______ method.

g. The volume of _______ is measured by using measuring cylinder.

3. Put a tick (√) for the correct statement and a cross (×) for the incorrect
one.

a. The SI unit of temperature is degree celsius.

b. The distance between any two points is called time.

c. One milliliter is equal to one cubic centimeter.

d. There are 10 years in 1 decade.

e. Objects having a definite geometrical shape are called regular objects.

14 Science and Environment Book - 7

f. The volume of a solid object is measured by using a graph paper.
g. Graph method is used to measure the volume of an irregular object.

4. Give one word.

a. Determination or estimation of physical quantities.
b. Objects having definite geometrical shape.
c. Region occupied by the surface of an object.
b. Total space occupied by an object.

5. Match the following physical quantities with their respective SI units.
length m3
mass kg
time m
area s
volume m2

6. Answer the following questions:

a. Define measurement with examples.
b. What is meant by SI unit? Mention any five physical quantities with

their SI units.
c. Define length. How can you measure the diameter of a spherical

object?
d. What is meant by the mass of the body? Write its SI unit.
e. What is meant by area of an object? How can you find out the surface

area of a leaf?
f. What is the space occupied by an object called? Write down its SI unit.
g. Name some of the devices that are used to measure volume.
h. How do you measure the volume of an irregular object? Explain.

7. Give reason for the following.

a. SI unit was developed.
b. A book is a regular object.
c. Graph paper is used to measure the area of an irregular body.

8. Differentiate between

a. Area and volume

Science and Environment Book - 7 15

b. Regular object and irregular object

c. Convex meniscus and concave meniscus

9. Solve the following numerical problems:

a. Find the area of a rectangle having length 13 cm and breadth 9 cm.

[Ans: 117cm2]

b. The length, breadth and height of a box is 8m, 5m and 3m respectively.

Calculate its volume [Ans: 120m3]

c. If the radius of sphere is 7 cm, find its volume. [Ans:1437.33cm2]

d. Find the volume of the cylindrical log of height 7m and radius 3m.

[Ans: 198m3]

e. Convert.

i. 1.5 kg to g ii. 30 cm into m iii. 5 days into second

f. Observe the given figure and calculate the areas of the leaves A,B, C

and D.

Note: Area of each square = 1 cm2

Project work

Take a small stone and measure its volume using water displacement
method.

16 Science and Environment Book - 7

2Lesson Force and Motion

Specific After the completion of the lesson, students will be able to:
Objectives
• define force and explain its effects.
• describe the various types of force with examples.
• introduce distance and displacement.
• define speed and velocity and describe uniform and variable velocity.
• define acceleration.
• solve some simple numerical problems related to speed and velocity.

Preliminary Syllabus
Concept
• Types of force,
Have you observed that a body can neither start or stop nor • Distance and
change its speed, direction or shape by itself ? Neither a body
can change its state of rest or motion, nor speed by itself. Let displacement,
us take a general example. • Uniform and variable

Football players often stop the ball travelling at a great speed. velocity,
Sometimes you also see a player deflecting the ball cleverly. • Acceleration,
Picking, opening, shutting, kicking, hitting, lifting, flicking, • Numerical problems of
pushing and pulling are some actions that usually result in
some kind of change in the motion of an object. speed and velocity

Hence, we conclude that a body requires force to start or stop
moving, change its speed, direction or shape. Thus, force is
something, which changes or tends to change the state of rest
or of motion of a body. In simple terms, we can define force as
a pull or push acting on a body which tends to change its state
of rest or of motion.

The state of motion of an object is described by its speed and
direction of motion. When the speed of the body is zero, it is
considered to be in a state of rest.

Science and Environment Book - 7 17

Introduction

Take a look and observe the things in your surrounding. You can see them
either moving or at rest. The table, white board, tree, door and window are in
rest while the vehicles on the road may be moving. Take a ball and keep it on
the ground, does it move? No, now gently kick it. Now the ball starts moving,
isn't it? It is because you apply the force on the ball to bring it into motion from
rest. Similarly, a desk does not move from its place unless you applied your
force to move it. When you go to school in the morning, you apply force to
lift your school bag and put it on your shoulders. When you enter a shop or a
bank, you may find PUSH and PULL written on the opposite sides of the door.
You push the door to get in and pull the door to come out. In the same way,
we need force to lift water from the well, open or close the door. The force not
only bring a body into motion from the rest but it can also bring the moving
body into rest. A goalkeeper can stop a ball moving towards him by applying
the force. So, we generally, pull or push the body to change its state. Hence,
the force is simply the pull or push of an object. A body is said to be in motion
when it changes its position with respect to the objects in its surroundings.

Force is a vector quantity as it has both magnitude and direction. The unit
of force is newton in SI system and dyne in CGS system. Force is measured
using a spring balance or by using the following relationship.

Force (F) = mass (M) × acceleration (a)
F =m×a

Force is usually denoted by the letter F. Force could be large or small. The
strength of a force is usually experienced by its magnitude. The direction in
which the body is pushed or pulled is called the direction of force.

Forces are due to interaction

For force to act, two objects must interact with each other. You can get the
concept of this by the following examples.

Sit on a bicycle and wait for it to move on its own. Will it move? It will not
move till you apply force on its pedals with your feet. In the same way, the
door of your cupboard will not open unless you apply force on it by pulling
with your hand. In the first situation, interaction between your feet and the
pedals makes the bicycle move. In the second situation, interaction between
the handle and your hand makes the door open. Hence, we can say that an

18 Science and Environment Book - 7

interaction between two objects is necessary for force to be effective. And,
there is a push or a pull involved when force is applied.

When more than one object apply force on another object in the same direction
the resultant force is the sum of all the forces applied. For example, when
two persons push a box in the same direction, it will move faster than when
pushed by one person, as shown in Fig b.

Suppose, the two persons start pushing the box in opposite direction (fig c).
What will happen? The box will either not move at all or move slightly in the
direction of the person who applies more force. This proves that if the two
forces act less in the opposite direction on an object, the net force acting on it is
the difference between the two forces.

Fig (a) Fig (b) Fig (c)

Effects of force

We have seen that force is a push or a pull acting on a body that changes its
state. Let us perform an activity to know what happens when force is applied
to different objects.

Activity 1 (Perform and observe)

To show the activities given in the table by applying force.

• Perform the activities given in the table by applying force.
• Write your observation in given table as shown in the first one.

Table: Effects of force

Activity Pull/Push Tick (√) the correct answer

1. Kick a football Push mov√es/bloats

2. Pedal your bicycle with more force speed increase/decrease

3. Hitting a moving ball move in same/ different direction

4. Roll dough into a chapati Speed/shape change

5. Stretch a rubber band Speed change/ size change

6. Catching a moving marble Comes in rest/move fast

Science and Environment Book - 7 19

From activity 1, we can conclude that force can

• make a stationary object to move.
• make a moving object to change its speed.
• make a moving body to change its direction of motion.
• change the shape and size of the object.
• make a moving body to come in rest.

Types of force

We cannot do any work without force. We apply various kinds of force to do
different works. There are many types of force. Some of them are discussed
here.

Pulling force

The force you apply to draw

the things towards you is called

a pulling force. For example:

when we draw water from a

well, we are applying a pulling Pulling cart Pulling door
force. Similarly, we use pulling

force while opening or closing a door, dragging things toward us and pulling

the cart wheel. It is easier to pull light objects than the heavy objects.

Pushing force

The force you apply to move the things away from you is known as pushing
force. For example, we use pushing force to push a stalled car, push a swing,
kick or throw a ball, squeeze a lemon etc.

Centripetal and Centrifugal force

When a body moves in a circular

path, it experiences two types of

force, one force that tries to pull

the body towards the centre and

other force that tries to pull it

away from the centre. The force

that acts toward the centre is Centripetal force Centrifugal force
called the centripetal force and

the force that acts away from the centre is called centrifugal force.

20 Science and Environment Book - 7

When you are riding a bicycle in a circular path, you bend towards the centre
due to the centripetal force. Similarly, when a bus is moving in a bend, the
passengers experience the force away from the centre. This is due to centrifugal
force. If the centripetal force is more, the body tends to move towards the
centre and if the centrifugal force is greater, the body tends to move away from
the centre. If there is a balance between centripetal and centrifugal force, the
body moves in a circular motion.

Activity 2

Tie a rubber ball or a wooden piece in about 100 cm
long thread. Hold the thread and rotate it in a circular
motion as shown in the figure and leave the thread
suddenly. Make sure your friends are not near you so
that they won't get hit by the object. As you leave the
thread, the object moves away from you. Why? While
you rotate the object holding the thread, the centripetal
force pulls the object and it moves in a circular path.
But as you leave it, the centrifugal force acts on it and
the object flies away from you.

Muscular force

The force exerted by the muscles of our body is Weight lifting
termed as muscular force. We use muscular force to
do different types of works. We use muscles of arms to
lift a load, pull heavy things. Similarly, we use muscles
of foot to walk, run or kick football. The animals like
horse, ox and donkey use muscular force to pull the
cart and carry the heavy loads.

Gravitational force

Hold your pen in your hand and just leave it. The pen drops on floor, isn't it?
Why did the pen move downward and not upward while it was free to move
anywhere? Anything we leave freely will eventually fall down to the earth even
if we throw it up in the air. It is because of the gravitational force. The earth
pulls everything towards its centre by a force of attraction called gravity. The

Science and Environment Book - 7 21

rivers flow from higher to lower land, Key Facts
the rippen fruits from the tree always
fall towards the surface of earth, the rain The gravitational force at
and snow also fall on earth because of the moon is approximately
the gravity of the earth. one-sixth that of the earth.
So, your weight on the moon
Like the earth, other planets, satellites will be one-sixth of your
and the sun also have their own gravity. weight on the earth.
The sun, the planets and their satellites
are held together by their gravitational
force.

Thus, the gravitational force is the force of attraction between two objects due
to their masses.

Activity 3

Take a rubber band and tie a medium sized stone to it. Let it hang. The
rubber band gets stretched as the earth pulls the stone towards it. Now tie
a bigger stone to it. What do you observe? The rubber band is stretched
even more. This proves that gravitational pull increases with the size and
weight of an object.

Amazing
Fact Gravitational force is an extremely useful force. We have learnt

that the force with which the earth attracts us is quite high and

because of this we do not fly off from the surface of the earth.

When we weigh any object using a spring balance, we measure the
gravitational pull on that object. More the force, the more will be the weight.
The moon is much smaller than the earth and its gravitational pull is also
quite less compared to the earth's. If your weight is 40 kg in earth, your
weight will be only 6.6kg on the moon. Remember, we are talking about
weight of an object, not the mass. The mass remains constant wherever you
go.

22 Science and Environment Book - 7

Magnetic force

The force exerted by a magnet upon the magnetic

substances is called magnetic force. The magnetic

substances like iron, cobalt, nickel, etc. are attracted

towards a magnet when they are kept close. This is

due to the magnetic force of the magnet.

As you have studied in earlier classes, the like poles Magnetic force

of magnets repel and the unlike poles attract each other. This attraction or

repulsion can be compared as a form of pull and push.

Magnetic forces are used in different electronic devices and to separate non
magnetic and magnetic substances from their mixture.

Do you know?

Magnetic force is used to run a train known as Maglev Train. This train
moves a few centimetres above the track due to the repulsion between the
magnets in the train and the track.

Electrostatic force

Take a comb and some small pieces of paper. Rub
the comb in hair and take it closer to the pieces of
paper. What do you observe? The pieces of papers
are attracted to the comb like magnet but it is not a
magnetic force. It is because of the electrostatic force.
Initially, the comb is electrically neutral but when it
is rubbed against the hair, it gets electrically charged due to the transfer of
the electrons from the hair. Here, the comb became charged and it attracts the
uncharged pieces of papers. Thus, the force exerted by an electrically charged
object is called electrostatic force. Charges can attract or repel each other like
magnets.

Frictional force

Frictional force is produced when two bodies are rubbed against each other.
It is the force that opposes the motion and therefore it stops or slows down
a moving body. It depends upon the roughness or smoothness of the surface
of the body in contact. Rough surfaces have more friction than the smooth

Science and Environment Book - 7 23

surfaces. Similarly, the heavier body produces more friction than a lighter
body. Frictional force acts in the opposite direction of the motion of the body.

Advantages of friction

Friction plays a very important role in our daily life. A few of its necessities are
as follows:
1. We are able to write on a paper due to the friction between the nib of the

pen and the paper.
2. We can walk due to the friction between our feet and the ground. It is

easier to walk in a rough surface than smooth or icy surface because the
rough surface offers more friction than the smooth surface.
3. The vehicles also run on the road due to the friction between tyres and
road. The tyres of vehicles are made gripped to increase the friction.
4. Friction also helps to apply the brake on the vehicles.
5. Friction helps the screw and nails to hold the things together.
6. It helps in cutting wood, burning matchstick, etc.
Disadvantages of friction

Friction is a necessary evil which causes the following disadvantages.
1. Friction reduces the efficiency of a machine. We need to apply lubricants in

machine to reduce the friction and increase efficiency of machines.
2. Friction produces heat resulting the wear and tear of moving parts of

machines.
3. The soles of our shoes and tyres of vehicle gradually tear due to friction.
Method to reduce friction

As the friction reduces efficiency of machines, it must be minimized. The
following methods are usually used to minimize friction.
1. Friction can be reduced by polishing the surface and making them smooth.
2. Oils and lubricants are used to reduce the friction in machines.
3. Ball bearing should be used in the moving parts of a machine as it is much

easier to roll a body than sliding it over a surface. It reduces friction to
great extent.

24 Science and Environment Book - 7

Circle Time

Form different groups and ask each group to collect evidence of forces acting
around us.

Scalar and vector quantity

The quantity having only magnitude but no direction is known as scalar
quantity. Length, mass, time, area, volume can be described by their magnitude
only. So, these are the examples of scalar quantities. The sum of scalar quantity
is always positive.

The quantity having both magnitude and direction is known as vector
quantity. It requires both magnitude and direction for its complete description.
Displacement, velocity, acceleration, force, weight are some examples of
vector quantity. A vector is represented by a straight line with an arrow head.
The arrow represents the direction of the vector and the length of the line
represents its magnitude. For example, vector AB is denoted by AB. The sum
of vector quantity may be positive, negative or zero.

Difference between scalar and vector quantity.

Scalar quantity Vector quantity

1. It has magnitude but not 1. It has both magnitude and
direction. direction.

2. Sum of scalar quantities is always 2. Sum of vector quantities can be

positive. positive, negative or zero.

3. It is represented by a letter only 3. It is represented by letter with an

i.e. A arrow on its head i.e. A .

4. Examples: length, mass, time, 4. Examples: displacement, velocity,
area, volume, etc. force, acceleration, etc.

Distance and displacement

The total length between two points is called the distance. Its SI unit is metre.
It is scalar quantity which refers to how much length an object has covered
during its motion. Displacement is the shortest distance between the two fixed
points. It is also measured in metre in SI unit and it is a vector quantity. Its
value can be zero but the value of distance is never zero.

Science and Environment Book - 7 25

Displacement refers to how far an object is displaced. It is actually the object's
overall change in position.Let's observe an example to make it clear about the
distance and displacement.

One of your friends walks 4 meter weast then 3 meter south, again 4 meter east

and finally 3 meter towards north. 4m

Even though your friend walked total

distance of 14 meter, but his actual 3m 3m

displacement is zero. During the course of

his motion, he covered the ground of 14m, 4m
yet when he finished walking, he is at the

same place i.e. there is no displacement for his motion. Displacement, being a

vector quantity, we must consider the direction. The 4m east cancels the 4m west

and the 3m south cancels the 3 m north. Thus, the final displacement is zero.

Speed and velocity

Speed and velocity are often used synonymously, but in physics they have
different meanings.

Speed is defined as the distance travelled by an object per unit time.

i.e. Speed = distance travelled (d)
time taken (t)

The SI unit of speed is metre per second (m/s). It is a scalar quantity.

Velocity is defined as the displacement of an object per unit time or the rate
of change of displacement.

i.e. Velocity = displacement
time taken

Its SI unit is also metre per second (m/s) but it is a vector quantity.

Difference between force and pressure

Speed Velocity

1. It is the rate of change of the 1. It is the rate of change of displacement.
distance.

2. It is a scalar quantity. 2. It is a vector quantity.

3. It is always positive. 3. It can be positive, negative or even zero.

26 Science and Environment Book - 7

Solved Numerical Problem

Example 1: A bus travelled 50 m in 10 second. What is the speed of the bus?

Solution

Distance travelled (d) = 50 m

Time taken (t) = 10 sec.

Here, we have,

Speed = distance travelled (d)
time taken (t)

= 50
10

= 5 m/s.
Thus, the speed of the bus is 5m/s.

Uniform velocity

An object is said to have uniform velocity if the direction of the motion and
the rate at which the object changes its position is constant. In other words,
an object with uniform velocity continues to cover the equal distance over the
same interval of time without changing its direction.

1sec 5m 2sec 5m 3sec 5m 4sec 5m 5sec 5m 6sec5m 7sec

In the given figure, the car is moving towards west from east and it covers
distance of 5 m in every second. Thus, the car is moving with a uniform velocity.

Variable velocity (non-uniform velocity)

If the distance covered by a body varies in each interval of time, it is called
variable or non-uniform velocity. Since, the velocity is a vector quantity, if the
object changes direction keeping its same speed, it is still considered to have
non-uniform velocity. Non-uniform velocity is more common than uniform
velocity in common life.

Science and Environment Book - 7 27

1sec5m 2sec5m 3sec4m 4sec 5m 5sec 2m 6sec 3m 7sec

In the given figure, the velocity of the car is varied in every second, so the car
is moving with non-uniform velocity.

Average velocity

Average velocity is the arithmetic mean of the initial velocity and final velocity
of a body. If the initial velocity of a body is considered as 'u' and the final
velocity be considered as 'v'. The average velocity is given by

Average velocity = u+v
2

Acceleration

A car moving in a crowded city road does not have a uniform velocity. During
the movement, a car may slow down or speed up at different time interval.
When the velocity of an object changes in such way, it is said to be moving
with acceleration.

Acceleration is defined as the rate of change of velocity of a body. It is generally
represented by 'a'.

Mathematically.

change in velocity
Acceleration (a) = time taken

= Final velocity (v) - initial velocity (u)

time taken (t)

\a= v-u
t

The SI unit of acceleration is m/s2. As acceleration is a vector quantity, its value

can be positive, zero or even negative. The negative acceleration is known as

retardation. If a car is travelling in a straight line and its speed increases, the

acceleration is positive and if the car slows down, its acceleration is negative.

In case of a uniform velocity, the acceleration is zero.

28 Science and Environment Book - 7

Solved Numerical Problem

Example 2: The velocity of a car changes from 10m/s to 20m/s in 5 seconds.
What is the acceleration of the car?

Solution:

Initial velocity (u) = 10m/s
Final velocity (v) = 20m/s
Time taken (t) = 5 sec
Acceleration (a) =?

Now, we have,

Acceleration (a) = Final velocity (v) - initial velocity (u)
time taken (t)

= 20 - 10
5
= 10
5

\ The acceleration of the car is 2m/s2.

Points to remember

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

2. SI unit of force is newton and denoted by N.
3. The force applied to draw the things towards us is called pulling

force.
4. The force applied to move the things away from us is called pushing force.
5. The force acting towards the centre of a circle is called centripetal force.
6. The force acting away from the centre of a circle is called centrifugal force.
7. The rate of change of distance is called speed and the rate of change of

displacement is called velocity.
8. If a body covers equal displacement in equal interval of time, then the

body is said to have uniform velocity.
9. The rate of change of velocity is called acceleration. Its S.I. unit is m/s2.
10. The negative acceleration is known as retardation.

Science and Environment Book - 7 29

Exercise

1. Choose the best answer from the given alternatives.

a. What is the unit of force in CGS system?

i. newton ii. pascal iii. dyne v. watt

b. Force applied on a moving body may__________.

i. bring it to rest ii. decrease its speed

iii. increase its size iv. all of these

c. If we apply force in the direction of motion of a body, then the body
will __________.

i. stop moving ii. move with increased speed

iii. move with decreased speed iv. move in a different direction

d. What do we call for the force of attraction between two bodies?

i. gravity ii. pulling force

iii. magnetic force iv. gravitation

e. Frictional force can be reduced by__________.

i. polishing ii. using lubricants

iii. using ball bearing iv. all of the above

f. Which of the following is a vector quantity?

i. distance ii. speed iii. length iv. velocity

g. The rate of change of distance is called__________.

i. speed ii. velocity iii. displacement iv. acceleration

2. Fill in the blanks with correct words:

a. The force that acts away from the centre of a circle is
called__________.

b. The force by which the earth pulls everything towards it is
called__________.

c. Frictional force is great in__________surface than__________surface.
d. Vector quantities have __________ and __________.
e. The SI unit of velocity is __________.
f. Acceleration is the rate of change of __________.
g. Negative acceleration is called __________.
h. The SI unit of acceleration is __________.

30 Science and Environment Book - 7

3. Put a tick (√) for the correct statement and a cross (×) for the incorrect one.

a. Force can change the direction of a moving object.
b. Earth pulls everything towards its centre.
c. A charged body attracts another charged or uncharged body because

of the electrostatic force.
d. Rough surface increases the frictional force.
e. Weight of a body does not change from place to place.
f. Displacement is a scalar quantity.
g. Velocity of a body can't be negative.
h. The acceleration of a body moving with uniform velocity is zero.

4. Match the following.

Pulling force Scalar quantity
Magnetic force Piece of paper attracted to a comb
Electrostatic force Vector quantity
Speed Drawing of water from well
Velocity Attraction of magnetic substance by magnet
5. Give one word.

a. The total length covered by a body during its motion
b. Shortest distance between two points
c. Rate of change of distance
d. Rate of change of displacement
e. Rate of change of velocity
6. Answer the following questions.

a. Define force and give its standard unit.
b. Can force act without an interaction between two objects? Explain

with an example.
c. What are the effects that force can produce? Give one example of each

effect.
d. What is pulling and pushing force?
e. What happen when centripetal and centrifugal force are balanced?
f. What is gravitational force?
g. What is frictional force? Write down its two advantages and

disadvantages.
h. 'Friction produces heat'. Write two advantages of this property.

Science and Environment Book - 7 31

i. What do you mean by uniform velocity?
j. Define acceleration. Give its mathematical formula and SI unit.

7. Differentiate between.

a. Centripetal and centrifugal force
b. Magnetic force and electrostatic force
c. Vector and scalar quantity
d. Speed and velocity
e. Uniform and non-uniform velocity

8. Give reason of the following:

a. A cyclist inclines while cycling in a circular path.
b. A piece of stone thrown up towards the sky comes back to earth.
c. A comb rubbed against the dry hair attracts the small pieces of paper.
d. We use lubricating oil in machines.
e. Displacement is called a vector quantity.

9. Solve the following numerical problem.

a. A car covers 800 m in 40 sec. What is the speed of the car?

[Ans: 20 m/s]

b. A bus covers distance of 72 km in 2 hours. Calculate the speed of bus.
[Ans: 10 m/s]

c. If a velocity of a car is 20 m/s, how much distance will it cover in 20

seconds? [Ans: 400 m]

d. If the velocity of a bicycle is 10 m/s, how long will it take to cover a

distance of 18 km ? [Ans: 1800 s]

d. If the velocity of a bus increase from 10 m/s to 25 m/s in 5 seconds.
[Ans: 3 m/s2]
What is the acceleration of the bus?

Project work

• Make a track of 100 m distance. Make some of the students to run across the

track one by one. Record the time each student took to complete distance
and calculate their velocity.

32 Science and Environment Book - 7

3Lesson Simple Machine

Specific
Objectives After the completion of the lesson, students will be able to:

• define a simple machine and list the ways by which simple machine makes our work
easier.

• identify and define different types of simple machine.
• explain the application of different kinds of simple machine.
• solve numerical problems related to simple machine

Preliminary Syllabus
Concept
• Introduction of simple machine
We human beings are always seeking for the new • Types of simple machine
ideas to make our life easier and more convenient.
The superior and intellectual mind of human beings • Lever
have invented thousands of such machines and • Pulley
equipments that make our day-to-day work more • Wheel and axle
easier. We can perform any work easier, faster and • Inclined plane
with more precision with the help of a machine. We • Screw
are actually surrounded by machines everywhere. • Wedge
Human beings have developed different machines for • Application of simple machines
different tasks. It is not necessary that the machines in our daily life.
should be complex and sophisticated. The simple
equipments like the pen you are writing with, the
spoon you eat with, the sharpeners, the staplers,
nailcutters all are the machines. The household
equipments like scissors, knife, fork, broom, shovel,
etc. and the complex machines like television,
computer, smartphones, vehicles, aeroplanes, etc. all
are machines.

Science and Environment Book - 7 33

Introduction

We use different kinds of devices and instruments. By using these devices,
work becomes easier, faster and more convenient. For example, we use a
straight rod to lift big objects, a screw jack helps us to lift the axle of a car, a
knife to cut vegetables. All these devices which are used in above examples
for doing work are simple machines. Thus, a simple machine is a device
having simple structure which makes our work easier, faster and more
convenient.

Scissors Knife Bottle openers Nail cutter

The simple machine makes our work easier in following ways.

1. The simple machine can multiply the force applied.
2. It can change the direction of the force applied.
3. It can transport effort from one point of the machine to another point.

Most of the machines which look quite intricate are either the modification of
a simple machine or a combination of two or more of them.

On the basis of the structure and the uses of the machines, they are classified
into six types which are described here.

Lever

A lever is a rigid bar which is free to turn about a fixed point called fulcrum. It
is a simple machine used to lift heavy loads with minimum amount of effort.
The object which is lifted by a lever is called the load and the force applied to
lift the load is called effort. For example, it is quite difficult to lift or move a
heavy stone with hands or only with the help of a rod. But if a small stone is
kept as a support below the rod as shown in the figure and the force is applied
from the other end, the stone moves with less effort.

34 Science and Environment Book - 7

In the given figure, the bigger stone is the load,
the smaller stone in the middle is fulcrum and
the force applied at the other end of the rod is
the effort. Longer the rod of the lever easier
will be to move the load. Placing the fulcrum
closer to the load also reduces the effort to
move it.

On the basis of relative positions of the fulcrum, load and effort, levers are
divided into three different classes.

First class lever

The lever in which the fulcrum lies in
between effort and load is called first
class lever. Scissors, trolley, pliers,
claw hammer, beam balance, sea-saw
are few examples of first class lever.

Scissors Beam balance Sea - saw

Activity

A simple experiment to show the working of a see-saw

Take a pencil, a small wooden box, a 50 cm ruler, three erasers of equal size
and cellophane tape. Fix the pencil on the box with the help of cellophane
tape. Mark a line across each eraser with the help of your ink pen as shown
in the figure, this line must be dividing each eraser into two equal parts.
We can call it a central line. Then balance the ruler across the pencil. Now
place one eraser near one end of the ruler and two erasers (one on top of
the other) on the other side.

Science and Environment Book - 7 35

Adjust the position of those erasers such
that the ruler is balanced. Now measure
the distance from the pivot (the point
of support of ruler on the pencil) to
the position of erasers and record your
measurement in table. Change the location of the single eraser and repeat
the experiment three to four times.

Table : Distance of erasers from pivot

1 eraser 12cm 8 cm 6 cm ...
2 eraser ...

Second class lever

The lever in which the load lies in
between the fulcrum and effort is
known as second class lever. Examples
of second class lever are bottle openers,
nutcracker, wheel barrows, lemon squeezer, etc.

Cart Bottle opener Lemon squeezer

Third class lever

The lever in which the effort lies between
load and fulcrum is called third class
lever. Fishing rod, tongs, shovel, spade,
forceps are some examples of third class
lever.

The distance between the fulcrum and load is known as load distance or load
arm and the distance between fulcrum and the point where effort is applied is
known as effort distance or effort arm.

36 Science and Environment Book - 7

Stapler Shovel Fishing rod Forceps

Similarly, the work done on a machine is known as input work and the useful
work done by the machine is known as output work. When the lever is in
equilibrium condition, input work is equal to output work. It is the principle
of the lever. i.e.

ie. input work = output work.
effort × effort arm = load ×load arm.

A lever of the first class multiplies force
if the effort arm is longer than the load
arm. Let's observe it by the following
activity.

Activity 2

To demonstrate that first class
lever multiplies force if the
effort arm is longer than the
load arm.

Take a uniform wooden scale
PQ of about 50 cm length as
shown in the figure. Support the wooden scale on a wedge of a suitable
height at its centre i.e. 25 cm mark. Now, place a block of weight W (say
100g) at the point B to serve as a load. Now, balance this load by applying
an effort E at the point A such that AC > CB. The effort (E) = weight
suspended from the point A.

Find the effort (E) for different loads (W) placed on the point (A). Find the
ratio of effort (E) to the load (L) lifted every time. Since AC < CB,

E<L

The effort E has been multiplied to lift the weight L.

Science and Environment Book - 7 37

Advantages of Lever

To perform different types of work, we use different instruments in our daily
life. Lever is a type of instrument which is used by us in many fields. Lever is
a rigid or hard bar, it may be bent or straight. Lever is basically used for lifting
objects or loads.

1. Lever makes our work easy.
2. Less force is used to work with lever.
3. We can lift heavy load with the help of lever.
4. It is also used to speed up the rate of work.

Pulley

A pulley is a simple machine that consists of a grooved rope or a chain wrapped
around a wheel. It changes the direction of force and thus makes it easier to lift
the things to some height. In a pulley, load is connected to one end of the rope
and the effort is applied at the other end of it. When the effort is applied, the
disc starts rotating. Pulley is used to draw water from a well, raise a flag on a
flag pole, lifting loaded goods to certain heights for different purposes.

There are three main types of pulley- fixed pulley, movable pulley and
combined pulley.

a. Fixed pulley

The pulley which remains attached to a

hook or a wall and does not move along

with the load is called fixed pulley. A

fixed pulley can change the direction of

the force applied, but it does not increase Fixed pulley

the amount of force. Such pulley is often used in drawing water from a well

and uplifting the flagpoles.

b. Movable pulley

The pulley which moves with the load is Movable pulley
called movable pulley. It is not attached
to a fixed point. One end of the rope is
fixed at a point and the effort is applied
at the other end. The advantage of a
movable pulley over a fixed pulley is that

38 Science and Environment Book - 7

it can multiply the force and thus reduce the effort used to pull load. Example
of movable pulley are cranes and block and tackle pulley in sailing boat.

c. Combined pulley

The pulley which is formed by the combination Combined pulley
of both fixed pulley and movable pulley is
termed as combined pulley. It is capable of both
changing the direction of a force and magnifying
the effort. Greater the number of pulleys and
supporting ropes, smaller the force required.

Wheel and axle

A wheel and axle consists of two wheels of different diameters and capable
of rotating about a common axis. The cylinder with a large diameter is called
the wheel and of smaller diameter is called the axle. It is a simple machine in
which a large wheel rotates along the centre or axle. An axle is attached at the
centre of a larger wheel. Both the wheel and axle must move together to form
a simple machine. The effort applied to the wheel helps in turning the axle and
vice-versa. Wheel and axle are used to lift and move objects. The example of
wheel and axle are the steering of a car, knob of a door, screwdriver, pedal of a
bicycle, etc. The windlass used to lift water from wells is an application of the
wheel and axle. The capstan used in ships to raise the anchor also works on the
principle of the wheel and axle.

Steering of car Knob of door Pedal of bicycle
Inclined plane

An inclined plane is a simple machine with a slanted or sloping surface which
connects lower level to higher level. It is used to move a heavy object from
lower place to higher place and vice-versa. An inclined plane does not reduce
the amount of work done but makes it easier to do. It is definitely easier to roll
a heavy drum through an inclined plane into a truck rather than lifting it with
hands all the way. A wheelchair can be easily pushed up by an inclined plane

Science and Environment Book - 7 39

in a hospital. A winding mountain road is also an inclined plane. Buses and
ears will not be able to run straight on steep roads. So, winding roads with
gradual stepes are built. A wooden plank, stair cases, wind roads on the hills,
children's slides on playground are some examples of inclined plane.

Ladder Inclined plank Slide
Activity

To show the effort required to pull a body up on inclined plane depends

upon the length if height is the same.

Material Required: Plank of wood, spring balance, small trolley

Procedure: C

1. Make an inclined plane like the one
shown in the figure. The length of
the inclined plane is adjustable but its
height is fixed.

2. Find the weight of a small trolley with lh B
the help of a spring balance. q

3. Adjust the position of the vertical A
support so that effective length of
inclined plane is 60 cm. support

4. Connect the spring balance to a hook attached to the trolley placed on

the inclined plane.

5. Pull the trolley on the inclined plane with the help of the spring balance.

Read the spring balance when the pulley just starts moving upwards.

6. Repeat the activity by changing the length of the inclined plane.

The reading of the spring balance every time gives the effort being applied.
What conclusion do you draw from these observation?

Conclusion: From these observations it is concluded that when the length
of the plane is reduced, more effort has to be applied to move the trolley
upwards.

40 Science and Environment Book - 7

Screw

A screw is a simple machine which is actually a modified form of an inclined
plane wrapped around a rod spirally. It looks like a nail having a winding edge
known as thread. The distance between two successive threads is called pitch.
A screw is commonly used for holding things together and lifting materials.
The threads of screw interlock the two things in such a way that they cannot
be separated. Similarly, a jackscrew is used to lift the automobiles and heavy
objects. Screw, nail driller, jackscrew, etc are the examples of screw.

Screw nail Nail driller Jackscrew

Wedge

A wedge is a simple machine with at least one slanting side ending in a sharp
or pointing edge. The sharp edge is used for cutting, splitting, piercing and
drilling holes. The other side of the wedge is blunt where we apply the effort
to get the desired results. Knife, axe, sickle, razor, etc are the examples of
wedge.

Knife Khukuri Axe

Science and Environment Book - 7 41

Solved Numerical Problems

Example 1: Calculate the effort (E) from the given figure

Solution:

Load (L) = 600 N

Load distance (LD) =4m

Effort distance (ED) = 6 m

Effort (E) =?

Now,

According to the principle of lever

E × ED = L × LD

or, E × 6 = 4 × 600

or, E = 4 × 600
6

\ E = 400 N.

Therefore, the effort to be applied is 400 N.

Example 2: Find the effort distance if 100 N effort is applied to lift the load of
800 N at a distance of 40 m.

Solution

Load (L) = 800 N
Effort (E) = 100 N
Load distance (LD) =4m
Effort distance (ED) =?

Now, according to the principle of lever,

L × LD = E × ED
or, 800 × 4
= 100 × ED
or, ED
= 4 × 800
\ ED 100

= 32 m

Thus, the effort distance is 32 m.

42 Science and Environment Book - 7

Points to Remember

1. The devices which make our works easier, faster and more convenient
are called simple machines.

2. Simple machines are used to multiply the applied force, change the
direction of the force and to apply the force at a convenient point.

3. A lever is a rigid bar which can move freely about a fixed point.
4. The principle of a lever states that, in an ideal machine,
Load × Load distance = Effort × Effort distance
5. Fulcrum lies between load and effort in first class lever.
6. First class lever multiples force if the effort arms is longer than the

load arm.
7. Load lies between fulcrum and effort in a second class lever.
8. Effort lies between load and fulcrum in a third class lever.
9. A pulley is a simple machine made with a chain or a rope wrapped

around a disc.
10. Wheel and axle consist of two co-axial cylinders of different diameters.
11. Inclined plane is a slanted or sloping surface which connects lower

level to higher level.
12. A screw is a modified form of an inclined plane wrapped around a

rod spirally.
13. A wedge is a simple machine having a sharp or a pointed end.

Exercise

1. Choose the best answer from the given alternatives.

a. Which of the following is a first class lever?

i. scissors ii. nutcrackers iii. wheel barrow iv. fishing rod

b. A force applied to a machine to do work is called________.

i. output ii. input iii. load iv. effort

Science and Environment Book - 7 43

c. Which of the following is an example of a inclined plane?

i. Axe ii. stairs iii. jack screw iv. spoon

d. Which of the following is a modified form of an inclined plane?

i. lever ii. screw iii. pulley iv. wheel and axle

e. A knife is an example of

i. screw ii. lever iii. wedge iv. pulley

2. Fill in the blanks with correct words.

a. _________ is a fixed point about which a lever can rotate.

b. Crow bar is an example of _________ class lever.

c. Shovel is an example of _________ class lever.

d. The _________ the rod of the lever, the easier it is to move the load.

e. _________lies between_________ and_________ in a first class lever.

f. A_________ is used to draw the water from a well.

g. The _________ looks like a nail with grooves cut on it.

h. Knife and axe are the examples of_________.

3. Put a tick (√) for the correct statement and a cross (×) for the incorrect
one.

a. Simple machines make our work, easier and faster.

b. A simple machine can perform work without applying any effort.

c. In a second class lever, effort lies between load and fulcrum.

d. Wheel barrow is an example of a first class lever.

e. A simple machine can change the direction of the force applied.

f. Wheel and axle are made of two co-axial cylinders of different
diameters.

g. An inclined plane is used to lift the automobiles.

h. A screw is a modified form of an inclined plane.

i. An axe is a good example of wedge.

44 Science and Environment Book - 7

4. Match the following.

First class lever axe

Second class lever shovel

Third class lever steering of a car

Wheel and axle bottle opener

Inclined plane sea-saw

Wedge winding road

5. Which machines would you use to do the following works? Write their
types if any.

a. To draw water from the well

b. To cut a piece of paper

c. To cut the vegetable

d. To lift a car

e. To go to the upper floor

6. Answer the following question.

a. Define simple machines. How do they make our work easier?

b. State four objectives which can be achieved by a machine.

c. List the types of simple machines. Give two examples of each of them.

d. What is a lever? State the principle of lever.

e. Define the types of lever with two examples of each.

f. Write in short about different types of pulleys.

g. What is pulley? What are the uses of pulley in our daily life?

h. Define wheel and axle with examples.

i. What is an inclined plane? Give any three examples.

j. Define screw. What is meant by pitch and thread of a screw?

k. Define wedge. Name any three wedges which are used in our daily
life.

Science and Environment Book - 7 45

k. Draw the labelled diagram for the following.

i. pulley ii. wheel and axle iii. screw

7. Give the reason of the following:

a. Third class lever cannot magnify force.

b. Scissors are known as first class lever.

c. The steering of a car is called a wheel and axle.

d. Road in the hills are made winding.

e. Wedge is called a simple machine.

f. Wheel and axle is called continuous lever.

8. Differentiate between.

a. First class lever and second class lever.

b. Input work and output work

c. Pulley and wheel and axle.

d. Fixed pulley and movable pulley.

9. Solve the following numerical problems.

a. A load of 2000 N can be lifted by applying an effort of 350 N. If the

load arm is 35 cm, calculate the effort arm. [Ans: 200cm]

b. The load of 210 N is balanced by using a beam. If the load is at 40 cm

and effort at 80 cm away from the fulcrum, find the effort applied to

balance it. [Ans: 105N]

c. An effort of 40 N is applied to lift a load. If the load arm and effort arm
are 20 cm and 80 cm respectively, calculate the load. [Ans: 160 N]

d. Mansoon and Shreya are playing a see saw. Mansoon is sitting 80 cm

away from the fulcrum and Shreya is shifting 60 cm away from the

fulcrum. Calculate the effort that Mansoon should apply to lift Shreya

if the weight of Shreya is 420 N. [Ans: 315 N]

e. Saru of weight 250 N and Saroj of weight 350 N are playing a seesaw.

Saru sat on the see saw 2 m away from the fulcrum. How far from the

fulcrum should Saroj sit to lift Saru? [Ans: 1.4 m]

46 Science and Environment Book - 7