Modern Concept Science and Technology 7

Approved by the Government of Nepal, Ministry of Education, Curriculum Development
Centre, Sanothimi, Bhaktapur as an additional material for school

MODERN CONCEPT

SCIENCE
AND ENVIRONMENT
7

Authors
Chinta Mani Panthee

M.Sc., B.Ed., Ph.D. Scholar

Janak Raj Pant Kamal Neupane

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

Nova Publication (Pvt) Ltd.

Satungal, Kathmandu, Nepal

Tel: 0977-1-4230545

MODERN CONCEPT

SCIENCE
AND ENVIRONMENT

Publisher & Distributor 7

Nova Publication (Pvt) Ltd.
Satungal, Kathmandu, Nepal

Tel: 0977-1-4230545

Authors Chinta Mani Panthee
Kamal Neupane
Janak Raj Pant


Editor Romharsh Panthi


Edition First 2075
Revised 2076


Copyright Chinta Mani Panthee


Computer Layout
Sanjay Suwal, #9843159467

Printed in Nepal

Science is a systematic study of the phenomena occurring in our surrounding. Teaching science in the
classroom is not a rote learning process but it is a great achievement to the students for understanding the
facts, concepts, laws and principles. The effective teaching-learning activities help students to achieve the
goals of life by gaining knowledge, skills and values of life. Therefore, various teaching learning activities
can be adopted to science according to nature of the branch, area, topic and sub-topics. For effective teaching
learning process teachers are expected to emphasize the use of various teaching learning tools, technique
and materials. Teachers are also expected to use the local teaching learning materials as far as possible. To
achieve the goal of teaching learning process, we can adopt various methods according to situation, place
and interest of the students. So, teachers are the role model of the classroom.

If a teacher flies, then the students run.
If a teacher runs, then the students walk.
If a teacher walks, then the students sit.
If a teacher sits, then the students sleep.

Facilitating Learning
Facilitating learning includes the teaching learning processes which are easier, faster and sustainable.
Teachers need to facilitate true learning experience by using effective process of teaching-learning activities.
The teaching learning facilitation process includes different methods. Some of them are given below.

i. Lecture method: Oral presentations to a large group of passive students contribute very little to
real learning. In most of the cases of group teaching, lecturing skills and experience of the teachers do
not correlate students’ grades. Despite the limitations of the lecture method, it is an alternative method
in a situation with limited resources.

ii. Discussion method: The level of students’ participation in learning activities is expected more in
a discussion method. It can be:
a. Teacher- centered: Here, students answer the teacher's questions.
b. Student-centered: In this method, students address to each other, and the teacher mainly
guides the discussion towards the important points.

iii. Demonstration method: It is an effective way to illustrate concepts in the class. Mostly, the use
of everyday objects for the demonstration of scientific phenomena is more effective. Students'
interest is increased if they are asked to make predictions about the possible outcomes. In this
method, the teacher’s careful attention to engage all students is mandatory. Otherwise, it may
result in a passive learning.

iv. Question-answer method: Questioning is an old strategy. The steps of this method are:
a. Prepare questions and arrange them in a logical sequence to increase the curiosity of the
students.
b. Ask new questions by linking them with the learners' response.

v. Field Study: Teaching various natural phenomena in a scientific way becomes more effective
when students learn by going on a real field visit. Field visits to botanical gardens, research centers,
industries, zoo, etc. are important in the sense of real learning through experience.

vi. Experimental method: Teaching science without an experimental method is not an effective
teaching-learning activity. Experimentation is essential for scientific knowledge and understanding.
For the positive change in the concept, skill or attitude of the students and their performance in
their life, every activity is supposed to be an essential part for every teaching learning process.
Teachers are expected to make more and more involvement of the students in different activities
that help them to experience themselves for their further improvement.

vii. Management of teaching learning activities: For teaching learning activities, the weightage of
curriculum is determined 5. It is generally estimated that, in a year, the teaching learning activities
will be minimum 175 periods. Out of these, 140 periods (80%) are alloted for theory and 35
periods (20%) are alloted for practical. The period division of different areas of science and
environment is given in the following table.

S.N. Area Weighting (in %) Theory periods Practical periods

1. Physics 26 36 9

2. Chemistry 22.5 32 8

3. Biology 20 28 7

4. Geology and Astronomy 11.5 16 4

5. Environment education 20 28 7

Total 100 140 35

viii. Examination: The examination mechanism is equally important along with the course of study.

a. Theoretical Test: Weighting of marks assigned to the theoretical test is 75 marks. It is divided
into five branches of class 7 science and environment. They are as follows.

S.N. Branches Weighting (in %) Weighting (in marks)
1. Physics 33.3 25
2. Chemistry 20 15
3. Biology 20 15
4. Geology and Astronomy 6.7 5
5. Environment education 20 15
Total 100 75

b. Practical Test: Practical evaluation must be done on the basis of the following bases.

1. Drawings/Labellings/ Explaining characteristics
2. Record of practical work
3. Model Designing/ materials construction and their uses
4. Mini Project Work
5. Viva voce

Weighting of marks assigned to the practical test is 25 marks. The criteria and the corresponding marking
scheme are as follows:

S.N. Criteria Weighting (in marks)
1. Drawings/Labellings/ Explaining characteristics 5

2. Record of practical work 5

3. Model Designing/ materials construction and their uses 5

4. Mini Project Work 6

5. Viva voce 4
25
Total

ix. Grading: In this system, alphabets A, B, C, D and E are used in place of percentage to grade the
performance of students in their examination. CDC, Nepal has introduced nine grades to show the
performance of students.

Percentage obtained Grade Grade Description Grade Point
90 % - above 90% A+ Outstanding 4.0
80 % - less than 90 % A Excellent 3.6
70 % - less than 80% B+ Very Good 3.2
60 % - less than 70 % B Good 2.8
50 % - less than 60 % C+ Above Average 2.4
40 % - less than 50 % C Average 2.0
30 % - less than 40 % D+ Below Average 1.6
20 % - less than 30 % D Insufficient 1.2
Less than 20 % E Very Insufficient 0.8

a. Grade Point (GP) Calculation: For every grade, there is a specific grade point (GP)
associated with it. Each grade point is the upper limit point within its class. For example, if
anyone gets 90 marks and above in any individual subject then he/she gets an A+ grade in that
subject with the grade point 4.0.

b. Grade Point Average (GPA) Calculation: For this, the total GP of a student is divided by
the total number of subjects he/she appeared.

Guidelines to make questions papers:

Area No. of No. of Sub- Full K 30% U 30% A 30% HA 10%
questions questions marks

Physics 5 10 25 7.5 10 5 2.5

Chemistry 3 6 15 4.5 6 3 1.5

Biology 3 6 15 4.5 6 3 1.5

Astronomy and 1 2 5 1.5 2 0 1.5
geology

Environment 3 6 15 4.5 6 3 1.5
education

Total 15 30 75 22.5 30 14 8.5

Guidelines to select questions:
There are a total of four areas, from where we need to select questions. While selecting questions, we
consider the following action verbs and topics.

Area Useful verbs Sample questions
Knowledge
Understanding State, name, list, write, what, definition, What is….?, How many……?, Who…?, List
Application data, units, full forms, classification, the number of………..,State...?, Define.... , etc.
Higher Ability examples, labeling, etc. Write full form of......, Label the pars of......,Give
any two examples of....
Differentiate, Distinguish, Similarities,
Why, How, Explain, Parts of activity, Differentiate between…. and …., Write
Justify, compare, Short note, etc. similarities......, Write down characteristics......,
Give reason...... etc.
Uses, Application, Apply, Generalize,
Solve, Show, Use, Illustrate, Complete, Solve the given numerical problems. Complete
Examine, construct, Draw, Relate, the given chemical equations, Write down the
Transfer, etc. uses of, etc.

Derive, Verify, Argue, Discuss, Explain, Derive the formula……. , Explain an
Formulate, Criticize, Evaluate, Choose, experiment……, Analyse the....Formulate
Analysis, Determine, etc. the.....

Use of Technology in the Contemporary Teaching Strategy
The 21st century science teachers are concerned about preparing today's children for tomorrow's world. A major
challenge for the teachers is to meet the target of the 21st century learning outcomes. Teachers can use technology in
the classroom to exploit the learning of their students. It develops the interest of students in new theories
and inventions in the field of science.

i. ICT Guideline: Audio-video classes are more effective over lecturing methods. The use of smart
boards in classrooms, teaching softwares Online classes, are the practices to introduce technology
in teaching. A projector screen, computer, and sound system are required to use technology in a
classroom.

ii. Use of power point slides: Teachers can prepare Microsoft power point slides or directly download
from different sites. Some web links to search: www.slideshare.net , www.powershow.com, etc.

iii. Use of discs: Playing course related discs (DVDs) can help students in learning. Such discs are
available in the market.

iv. Use of videos or documentaries: Google search can give us links for so many videos like www.
sciencechannel.com . Similarly, free download of videos/ documentaries is possible from www.
youtube.com

Way to proceed the unit from this book
The first page of each unit drives the whole chapter.

i. The course of study issued by CDC and its learning objectives are given in the first page to keep
the teachers and students through their paces.

ii. The terms and terminologies on the same page are from screening of the chapter. It helps to
understand the whole unit. Teachers are expected to explain the difficulties of the students.

iii. Teachers can make students, follow the highlighted definitions, catchy memory plus box and
bubble box on the pages inside of a chapter for a quick look on important points to be remembered.

iv. Facts with reasons are given along with the sub-topic to understand the scientific concepts.
v. Before exercise problems, a practice of different level of questions (knowledge, understanding,

application, and higher ability) with their answer as answer writing skill is provided. After then,
students are allowed to do exercise from step 1 to step 3.

PREFACE

Modern Concept Science and Environment for grade 7 is written to meet the objectives of the curriculum
of class seven science and environment developed by CDC (Curriculum Development Center), Sanothimi,
Bhaktapur. This edition of our textbook meets the criteria of basic knowledge in science and environment
for students who study in class 7. It will help students to achieve the goals of life by gaining of knowledge,
skills and values in Science and environment.

Logical placing of key points and well organized matter are given high priority throughout the textbook.
Appropriate pictures, matter in simplified language and organization of the content with new features are
our high expectation values about popularity of this textbook among the readers.

Features of Modern Concept Science and Environment

A notable concern of many teachers is to follow a well-organized textbook with step by step learnings
in a continuous flow. The organization of this textbook is logically designed to make the book's
information more accessible.
1. Top of the first page of each unit consists of syllabus issued by CDC (Curriculum Development

Center), Sanothimi, Bhaktapur for class 7.
2. Learning outcomes of each unit are given just below the syllabus issued by CDC to focus the

teaching learning goals.
3. The most important idea of writing terms and terminologies on the first page of each unit is

devoted to screen out the main content to be covered.
4. Highlighted definitions, catchy memory tips and bubble box on pages inside of a chapter for a

quick look on important points to be remembered are provided in the first page of each unit.
5. Activities and solved numerical problems are given in each unit of the same page with

corresponding to the topic to develop the scientific skill in the readers.
6. Sample questions of Knowledge, Understanding, Application, and Higher Ability with their

answer are given at the end of each unit under the title answer writing skill to get idea to solve the
questions given in the three steps exercise.
7. This text book focuses primarily on all three level questions to test students' skill under the title
three steps exercise.

With these all features in a well-organized content, the central focus of this book is to encourage students
and make the text user-friendly for all. The answer writing skill and three levels grid based exercise will
help teachers to set test papers for assessments. Students' interest will be peaked when they will find the
screen out terms and terminologies, the appropriate pictures and key points throughout the textbook. We
hope that this book will help teaching in learner-centered way.

We wish to express our sincere gratitude to Mr. Megh Raj Poudel, Managing director of Nova Publication
Pvt. Ltd. for publishing this book. Similarly, thanks are due to Mr. Umesh Bajagain (Sudip), for his valuable
help during the preparation and content editing of the book. Likewise, thanks are due to Mr. Romharsh
Panthi for his praiseworthy language editing.

Finally, we owe full responsibility of misprints and other technical errors, if any, found in this textbook in
spite of our best effort to make this book error-free. Constructive criticism and suggestions for improvement
of this book will be highly appreciated.

5 Poush 2075 Authors
Kathmandu, Nepal

Table of Contents

Physics 1 Measurement 1-18
2 Force and Motion 19-38
Chemistry 3 Simple Machine 39-50
4 Pressure 51-57
Biology 5 Work, Energy and Power 58-70
6 Heat 71-88
Environment Geology & 7 Light 89-98
Education Astronomy 8 Sound 99-108
9 Magnet 109-120
10 Electricity 121-134
11 Matter 135-147
12 Mixture 148-161
13 Metal and Non-metals 162-169
14 Some Useful Chemicals 170-176
15 Living Beings: Animal Life 177-190
16 Living Beings: Plant Life 191-208
17 Cell and Tissue 209-223
18 Life Process 224-237
19 Structure of the Earth 238-250
20 Weather and Climate 251-263
21 The Earth and Space 264-275
22 Environment and Its Balance 276-300

23 Environmental Degradation and Its Conservation 301-317

24 Environment and Sustainable Development 318-324

UNIT Estimated teaching periods TheorMyoderPnraCcotniccaelpt Science and Environment - 7 1
51
1
Measurement

Syllabus issued by CDC Watch

 SI system of measurement
 Area of regular and irregular plane surfaces
 Volume of a liquid
 Volume of regular and irregular solids
 Simple numerical problems

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 introduce SI system of measurement and its use.
 calculate the surface area of regular and irregular objects.
 calculate the volume of regular and irregular objects.
 describe the method for measuring the volume of liquids and calculate their volume.
 solve simple numerical problems related to area and volume.

Key terms and terminologies of the unit

1. Measurement: Comparison of an unknown physical quantity with
the known and standard quantity of the same kind is
called measurement.

2. Local measurement system: Local measurement system is a system of
measurement in which we use locally developed
units for the measurement.

3. SI Units: SI Units is the most widely used international system
of measurement adopted by the international
convention of scientists held in France in 1960 A.D.

4. Physical quantities: The quantities which can be measured directly
or indirectly with the help of physical devices or
instruments are called physical quantities.

5. Fundamental quantities: Fundamental quantities are those quantities which
do not depend upon other physical quantities.

6. Derived physical quantities: Derived physical quantities are those quantities
which are obtained by combining one or more
fundamental physical quantities.

2 Measurement

7. Unit: The unit is a standard known quantity which is used to
compare other physical quantities of the same kind.

8. Fundamental units: The units of measurement which do not depend upon other
units of measurement and are used to measure fundamental
physcical quantities are called fundamental units.

9. Derived units: The units of measurement which depend up on fundamental
units of measurement are called derived units.

10. Length: Length is the distance between any two points.

11. One standard meter : One standard meter is the shortest distance between two
parallel lines on a platinum-iridium rod preserved at a
constant temperature and pressure in the International
Bureau of Weights and Measures at Sevres in Paris.

12. Mass: Mass is the total quantity of matter present in a substance.

13. One standard kilogram: One standard kilogram is the mass of a cylinder, made up of
platinum-iridium alloy, with its height equal to its diameter
that is kept in the International Bureau of Weights and
Measures at Sevres in Paris.

14. Time: Time is the duration between any two events.

15. One second of time: One second is defined as 1 th of a mean solar day.
86400
16. Area: The total surface covered by an object is called its area.

17. Volume: The total space occupied by an object is called its volume.

1.1 Introduction

In our daily life, we use measurements all the time. We measure distance, time and
mass every day. A carpenter measures the length of the wooden plank to make the
furniture. A shopkeeper measures the mass of sugar for selling it to the customer. The
speedometer shows the speed of a vehicle. These measurable quantities are physical
quantities.

Measurement is a comparison process. In order to measure a physical quantity, we
assume a certain magnitude of the same quantity known as the standard quantity.
This standard quantity is called ‘unit’. For example, to measure the length of a piece
of cloth, we compare it with a meter scale.

Modern Concept Science and Environment - 7 3

Beam balance Measuring cylinder Measuring tape Watch

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

In this unit, we will learn about the standard system MEMORY PLUS
of measurement and the standard and local units We cannot measure love, hate,
used in measurement of different physical quantities. emotion, etc. as they are non-
We will also learn about the measurement of area physical quantities.
and volume of regular and irregular objects.

FACT WITH REASON

Why do we measure a physical quantity?

We measure a physical quantity to know its exact magnitude. It helps us in selling, buying,
research, etc.

1.2 Importance of Measurement

1. Measurement of the different objects helps us in selling and buying them.
2. Measurement of our body parts is necessary for the tailor to stitch our clothes.
3. We need to monitor our body temperature as measured by the thermometer.
4. Medicine doses are measured and fixed.
5. Measurement makes scientific experiments possible.

1.3 Local System of Measurement in Nepal

Local Measuring Units Measured Physical Quantity
HAAT, BITTAA Length
PAAU, CHHAAK, SER, DHAARNI Mass
GHADI, PALAA Time

Mana Pathi Bitta

4 Measurement

In Nepal, units of measurement like HAAT, BITTAA, MAANAA and PAATHI have
been used since an ancient time. The local system of measurement uses the locally
developed units of measurement. As local systems of measurement may differ from
one locality to another, they make it hard for us to compare the results of these
measurements. To remove the demerit and bring uniformity in measurements, an
international system of units has been adopted throughout the world.

FACT WITH REASON

Why are local units of measurement no longer used?
Local units of measurement are developed locally to use in certain localities. As local systems
of measurement may differ from one locality to another, they make it hard for us for selling,
buying, comparison of result, etc. So, local units of measurement are no longer used.

1.4 International System of Units (SI Units)

A widespread acceptance of a specific system of measurement makes it easy for people
everywhere to compare the magnitude of physical quantities. The General Conference
of Weights and Measures held in Paris, France, in 1960 introduced the international
system of units. It is known in French as Le Systeme Internationale d’Unites, that is,SI
Units, in short. SI Units is the extended version of MKS (meter, kilogram and second)
system.

The system of measurement which was adopted by the international convention of

scientists held in France in 1960 A.D. is called SI Units. The units of measurement of

the physical quantities which are developed by this conference are called SI Units. For

example, the SI Unit of length is meter (m). MEMORY PLUS
MKS system was also originated in France.
Need of SI Units

In the past, people used different local units of measurement in different places.
However, with the growth of world trade, the need of standard units, all over the
world, became urgent. SI Units was a response to this need to bring uniformity in
measurements throughout the world. The international system of measurement has
also made it easy for us to understand the results of measurement in the same way
around the world.

FACT WITH REASON

Why is SI units established?
To bring uniformity in measurements throughout the world and to make selling and buying
easy, the SI units is established.

Modern Concept Science and Environment - 7 5

1.5 Physical Quantity

We can measure the length, breadth and height of a room with the help of a measuring
tape. The tape helps us to measure a physical quantity, i.e. the distance between
points. Thus, those quantities which are measured directly or indirectly with the help
of physical devices or instruments are called physical quantities. Mass, length, time,
area, volume, etc. are some examples of physical quantities.

FACT WITH REASON

Why cannot we measure sadness?
We cannot measure sadness because it is not a physical quantity.

A physical quantity can be represented by a number, followed by a unit.

i.e. Physical quantity = Numerical value × Unit

For example, when we say the length 400m, here the quantity 400 is the numerical
value and ‘m’ is the unit of length

Types of Physical Quantities

Fundamental Physical Quantities

Those physical quantities which do not depend upon other physical quantities are
called fundamental physical quantities. Examples: mass, length, time, temperature,
etc. Fundamental quantities are also called basic quantities.

Derived Physical Quantities MEMORY PLUS

Those physical quantities which depend upon 1. Temperature and Electric Current
fundamental physical quantities are called derived are fundamental physical
physical quantities. Examples: area, volume, density, quantities.
pressure, etc. Derived quantities are obtained by
multiplying or dividing two or more fundamental 2. Acceleration, force, velocity etc.
quantities. are derived quantities.

FACT WITH REASON

Velocity is a derived physical quantity. Why?

Velocity can be expressed as velocity (V) = displacement / time

Here, velocity depends up on two fundamental quantities, i.e. displacement and time. So,
velocity is a derived physical quantity.

1.6 Standard Unit

In ancient times, people used their foot, footstep, hand-span or arm to measure the
length. These units were not reliable because they varied from one person to another.
This led to the development of new units, which were more reliable.

6 Measurement

A unit is a standard known quantity which is used to measure the physical quantity
of the same kind. For example, meter (m), kilogram (kg), second (s), etc, are standard
units. These units are used all around the world.

FACT WITH REASON

The meter is a standard unit. Why?
The meter is considered a standard unit because its value is the same and acceptable
throughout the world.

Characteristics of Standard Unit MEMORY PLUS

i) The size of standard units should be convenient. 1 meter is equals to 100 cm.

ii) It should not change with time.

iii) The definition of a standard unit should cause no doubt or confusion.

iv) It should be applicable to measure derived quantities.

Types of Units MEMORY PLUS
Fundamental Units Unit of volume (m3) is a derived unit.

Fundamental units are independent units of measurement. Examples: meter, kilogram,
second, etc.

Fundamental Units of Measurement

Fundamental Quantity Fundamental Unit Symbol in SI Units
Length meter m
Mass kilogram kg
Time second s
Temperature kelvin K
Electric current ampere A
Luminous intensity of light candela cd
Amount of matter mole
mol.

Derived Units

Derived units are those units which are obtained by combining one or more fundamental
units. For example, square meter, meter/second, joule (J), Pascal (Pa),watt (W), etc.

FACT WITH REASON

SI units is called an extended version of MKS system. Why?
In SI Units, units of mass, length and time are the same as that of the MKS system. Along with
these three fundamental units, there are four new fundamental units introduced in the SI
Units. So, SI units is called an extended version of MKS system.

Modern Concept Science and Environment - 7 7

1.7 Length

Length is the distance between two points. For example, if the distance between two
ends of a pencil is 18 centimetre, then the length of the pencil is 18cm. The SI unit of
length is meter (m).

Standard One Meter

Standard one meter length is the distance between two parallel lines drawn on a
platinum-iridium rod, which is kept at a constant temperature in the International
Bureau of Weights and Measures at Sevres in Paris. All replicas of the meter are
compared with this standard meter.

Inch tape Ruler Measuring tape

Relationship between Multiples and Submultiples of the Meter

Submultiples of Meter Multiples of Meter
Decimeter (dm) = 10-1 m Decameter (dam) = 101 m = 10 m
Centimeter (cm) = 10-2 m Hectometer (hm) = 102 m = 100 m
Millimeter (mm) = 10-3 m Kilometer (km) = 103 m = 1000 m
Micrometer ( μm) = 10-6 m
Nanometer (nm) = 10-9 m MEMORY PLUS
Pico-meter (pm) = 10-12 m An inch is a commonly used unit of
length, which is equal to 2.54 cm. (1
FACT WITH REASON inch = 2.54 cm.)

Why is alloy of platinium-irridium used to make standard meter?

Platinium-irridium rod is used to make standard meter because it does not erode in normal
temperature and pressure.

Measurement of Length

Length can be measured by using instruments such as scales,tapes, etc. To measure
the exact length of an object, one of its ends is kept at the zero mark of the meter scale
and the reading is taken with our eye perpendicular to the reading.

8 Measurement

Incorrect Correct Incorrect

Method of measurement

Possible Errors in Measurement of Length MEMORY PLUS
i) Error in angle of view. Centimeter is the CGS unit of length
which is a French system.
ii) Error while adjusting the scale.

iii) Error from erased readings on the scale.

Incorrect (Wrong) measurement Correct measurement

Incorrect (Wrong) measurement Correct measurement

Things to Remember while Measuring Length
i) Length is measured from the zero mark of the scale or tape.
ii) The tape or scale is placed straight over the object, which is to be measured.
iii) The correct position of the eye is perpendicular to the reading mark.
iv) To measure the exact length with the help of a scale with erased ends, the

measurement should be taken from a certain point elsewhere.

Parallax error

It is an error that occurs due to incorrect position of eye while taking the reading. The
correct position of the eye is perpendicular to the reading mark.

ACTIVITY 1

Take accurate measurements of your book, notebook and pencil and write the results in
the table below.

Objects Measurement of Length

Book in millimeter in centimeter in meter in inch
Notebook

Pencil

Modern Concept Science and Environment - 7 9

Method to Measure External Diameter of a Sphere

i) The sphere is kept on a plane surface.
ii) Two wooden blocks, with plane surfaces, are placed on the opposite sides

touching the sphere.
iii) The distance between the wooden blocks is the external diameter of the sphere.

In the figure, diameter (d) of the sphere is equal to the difference between the readings
of the wooden blocks.

Football Spherical object
Solid block

FACT WITH REASON

The standard one meter length scale is kept at a constant temperature. Why?
Matters expand on heating and contract on cooling. The change in temperature affects the length
between two points. So, standard one meter length scale is kept at a constant temperature.

1.8 Mass

The total quantity of matter contained in a body is called its mass. It means that,
quantity of matter in an object is equal to the mass of the object. If a substance has less
quantity of matter, it has less mass. Similarly, a substance with more quantity of
matter has more mass. The SI Unit of mass is one kilogram (kg).

Standard One Kilogram MEMORY PLUS

Mass is a fundamental quantity.

A standard kilogram is the mass of cylinder made up

of platinum-iridium alloy of equal diameter and height, which is kept in the

International Bureau of Weights and Measures at Sevres in Paris. Accurate copies of a

kilogram are prepared by comparing it with the standard kilogram in Sevres.

Relationship between Multiples and Sub-multiples of the Kilogram

Sub-multiples of Kilogram Multiples of Kilogram
Decigram (dg) = 10-1 g 1 quintal = 100 kg
Centigram (cg) = 10-2 g 1 metric ton =1000 kg
Milligram (mg) = 10-3 g
Microgram ( μg) = 10-6 g

10 Measurement

Measurement of Mass

Balances are used to measure the mass of a body. There are several types of balances:

Beam balance Physical balance Grocery balance Digital balance

Traditional Two-Pan Balance (Beam Balance) or Lever Balance

A beam balance has two pans. One of the pans has labels on it. The substance to be
measured is kept on the other pan. The substance is added until the beam of the beam
balance becomes horizontal.

Things to Remember while Measuring Mass by a Beam Balance
i) Raising and lowering of the beam must be done gently.

ii) The beam of a beam balance should be horizontal before and after adding labels
and substance to be measured on its pans.

iii) The mass of a label must be mentioned clearly on it.

Electrical Balance

An electrical balance requires power supply to operate. It is a very practical tool to
use. We can see the smallest reading of weighing result directly on the screen of an
electrical balance.

FACT WITH REASON

Why do we use electrical balance?
We use electrical balance because it can measure the smallest changes in measurement of mass.

1.9 Time

Some terms often used when defining time are duration, period, interval, etc. The
duration between any two events is called time. Events mark the interval of time. For
example, the sun rises in the morning and it sets in evening. The sunrise and sunset
are two events. Second (s) is the SI Unit of time.

FACT WITH REASON

Why do scientists use atomic clock rather than pendulum clock?
Scientists use atomic clock instead of pendulum clock because atomic clock can measure
the smallest fraction of time but pendulum clock cannot.

Modern Concept Science and Environment - 7 11

One Second of Time

The average of time taken by the earth to complete one rotation on its axis is called a
mean solar day. Its duration is 24 hours (i.e. 86,400 s). One second is defined as 1 th
86400
of a mean solar day.

Measurement of Time

Time is measured by using different instruments. The clock is the most important one.
Different types of clocks or watches are:
a) Pendulum clock
b) Mechanical wrist watch
c) Quartz watch
d) Atomic clock
e) Atomic wrist watch

Pendulum clock Stop watch Wrist watch Digital clock

Relationship between second (s) and its multiples

60 seconds (s) = 1 minutes 7 days = 1 week MEMORY PLUS
60 minutes (min) = 1 hour 365 days = 1 year One day is equal to 86,400 seconds.

24 hours (hr) = 1 day 10 years = 1 decade

1.10 Regular and Irregular Objects

Those objects which have fixed geometrical shape are called regular objects. Examples:
book, box, brick, football, etc. We can measure the area and volume of the regular
objects with the help of formula. For example the area of a book is the product of its
length and breadth. Similarly, there are many objects in our surrounding which do
not have fixed geometrical shape. They are called irregular objects. Thus, those objects
which do not have a fixed geometrical shape are called irregular objects. Examples:
broken piece of glass, a piece of stone, a leaf, a piece of paper, etc. We use graph
paper to measure the area of the irregular objects and liquid displacement method to
measure the volume of these objects.

12 Measurement

Area

The total surface covered by an object is called its area. It means, area is the measure of the
extent of surface covered by the body. Area can be measured in the units of square meter,
square centimeter, square kilometer, etc. But, the SI unit of area is square meter (m2).

Area of Regular Plane Surface

An object with a fixed geometrical shape is called a regular object. For example, book,
copy, sphere, cylinder, etc. are regular objects. The area of a regular plane can be
determined by using formula. For example:

a) Area of a rectangular object = length (l) × breadth (b)

b) Area of a cube = 6 × (Length)2= 6 × l2

c) Area of a triangle = 1 base × height
2
Area of circular object = πr2
( )Solved Numerical 1.1
d) Where r = radius, π = 22
7

Calculate the area of a rectangular floor of a room having a length of 6m and breadth
of 4m.

Solution: Given,

The length of the rectangular floor (l) = 6m MEMORY PLUS
The breadth of the rectangular floor (b) = 4m When you solve a numerical
From the formula, problem, write the answers with the
Area = length × breadth correct unit.

Area = 6m × 4m = 24m2

So, area of the rectangular floor is 24 m2.

Area of Irregular Plane Surface

An object without a fixed geometrical shape is called an irregular object. Examples: a
piece of stone, broken piece of glass, leaf, etc. Area of irregular plane surfaces can be
calculated by using the graph paper.

Method to Calculate the Area of an Irregular Leaf
i) A leaf is placed on a graph paper.

ii) A pencil is used to draw the outline of the leaf as it
is on the paper.

iii) The leaf is removed from the graph paper. Now,
the number of complete square boxes, half squares
and squares occupying more than half of area in the
graph are counted from outline on the graph paper.

Modern Concept Science and Environment - 7 13

The squares occupying less than half of the area from outline are neglected.

Now, the total number of small squares inside the boundary = Number of
complete squares + Number of half squares + Number of squares occupying
more than half of the area from outline

iv) The number of squares counted from the outline on the graph paper gives the
area of the irregular plane surface. If counting of squares is done by considering
a square of one centimeter then the total area of the leaf is in square centimeters.

FACT WITH REASON

Why do we use graph paper to measure area of small irregular surface?
We use graph paper to measure area of irregular surface because we cannot use any standard
formula for irregular shape.

Volume

Volume is the measure of the space occupied by an object. The total space occupied
by a body is called volume of that body. It is measured in cubic meter (m3) or cubic
centimeter (cm3). But, the SI unit of volume is cubic meter (m3).

Relationship between Units of Volume
1 liter (lt) = 1000 milliliter (ml)

1 liter (lt) = 1000 cubic centimeter (cc) (1ml = 1 cc)

1 cubic meter = 1000 liter

Measurement of Volume

Measurement of Volume of Solids
Volume of regular solids can be determined directly by using a formula. For example,
a) Volume of a cube = side × side × side = l3

b) Volume of a cuboid = length (l) × breadth (b) × height (h) r
c) Volume of a sphere = 4πr3 (Where r = radius, π = 22)

37
d) Volume of a cylinder = πr2h (Where r = radius, π = 22)

7

h

O A h
OA= r
l l b Cylinder

Cube Cuboid Sphere

14 Measurement

Solved Numerical 1.2

The radius of a volleyball is 5cm. Calculate its volume.
Solution: Given,

The radius of the volleyball (r) = 5cm

According to the formula,
Volume of the volleyball, V = 4πr3 = 4 × 22 × 53 = 523.81 cm3

3 37
Therefore, the volume of the volleyball is 523.81 cm3.
Measurement of Volume of Liquid
Some measuring devices are used to measure the volume of liquid. It is often measured
in liters.
a) Measuring Jar: It is a cylindrical jar calibrated in ‘ml’ from its bottom to the top.

Such measuring jars are available in different capacities.
b) Measuring Flask: It is a round-bottomed flask with a long neck.
c) Burettes: Burettes are similar to measuring jars, with pinch cock at the end.
d) Pipettes: They are long narrow glass tubes with a spherical or cylindrical bulb

in the middle.
e) Milkman’s measure and oil dealer’s measure: They are of different capacities

with handle for holding.

Graduated Milkman’s Oil dealer’s Pipette Burette
cylinder measure measure

Volume of Irregular Solid Substances

Volume of irregular solid substances is measured by liquid displacement method
with the help of a measuring cylinder. This method is based on the principle that
when a solid object is dipped in a liquid, the level of the liquid rises. The volume of
the liquid displaced is equal to the volume of the object.

Meniscus

Normally the surface of a liquid in narrow tubes is slightly curved near the walls of
the container due to the phenomenon known as surface tension. This curved surface
of the liquid is known as meniscus. There are two types of meniscus.

Modern Concept Science and Environment - 7 15

a) Concave Meniscus: When liquids like water,
kerosene, alcohol, etc. which stick on the
walls of the container, are kept in the
measuring cylinder, the surface is depressed
in the middle and raised at the boundary.
Such a shape is called a concave meniscus.

b) Convex Meniscus: When liquids like Convex meniscus
mercury, which do not stick on the walls of Concave meniscus

the container, are kept in the measuring cylinder, the surface is depressed at the

boundary and raised in the middle. Such a shape is called a convex meniscus.

Method to Measure the Volume of Irregular Solid

i) Add some water in a measuring cylinder.

ii) Read the initial volume of water (V1) from the bottom of the curved surface of
the water level.

iii) An irregular object like a stone is immersed in water and the volume of water
with stone in it (V2) is measured.

Now, the volume of stone = V2 - V1
Solved Numerical 1.3

Find the volume of the stone shown in the given figure.

Solution: Given,

Here, Initial volume of water (V1) = 20 ml

Volume of water with stone in it (V2) = 23 ml

Now, Volume of stone = V2 - V1

= 23 ml – 20 ml

= 3 ml

= 3 cm3 ( Here, 1 ml = 1 cm3)

Things to Remember while Measuring Volume by Using a Measuring Cylinder

a) In case of liquids having a concave meniscus, MEMORY PLUS

volume is measured from the lower surface. The volume of the gas can be found

In case of liquids having a convex meniscus, by using water displacement method.

volume is measured from the upper surface.

16 Measurement

Wrong 100 Wrong 100
Correct 90 90
80 Upper
Wrong 70 meniscus Correct 80
60
70 Lower
60
50 50 meniscus

40 Mercury Wrong 40
30
30

20 20 Water
10
10

b) While measuring the volume, the level of eye height should just fall on the liquid
surface. If the height level is below the surface of liquid then the measured
volume will be less and if the height level of eyes is above the surface of liquid
then the measured volume will be more.

FACT WITH REASON

Volume of the irregular objects is measured with the help of a measuring cylinder using
water displacement method. Why?
When an irregular object is immersed in the water kept in a measuring cylinder, it displaces
water. The volume of water displaced is equal to the volume of the irregular object. So, liquid
displacement method is used to measure volume of the irregular objects.

STEPS EXERCISE

STEP 1

1. Tick () the correct statement and cross () the incorrect one.
a) Meter is a fundamental unit.
b) Kilometer is a sub-multiple of a meter.
c) SI Units was adopted in 2060.
d) Mercury has a concave surface.
e) Area of a cube is given by (side)3.
f) Area of an irregular surface can be found by using a graph paper.
g) One tonne of mass consists of 100 kilograms.

2. Fill in the blanks with appropriate words.
a) Quantities such as mass, length, volume and density are called … quantities.
b) Kelvin is the SI Unit of …… .

c) The SI Unit of area is …… .
d) …… is defined as the interval between two events.
e) Alcohol has …… surface.

Modern Concept Science and Environment - 7 17

STEP 2

3. Write one word answer.
a) Name the fundamental unit of mass in SI Units.
b) How many times larger is ‘kg’ than ‘g’?

c) What is the SI Unit of volume?
d) Which type of unit is meter/second?
e) What term denotes the total surface covered by a body?

4. Differentiate between:
a) Fundamental unit and derived unit
b) Area and volume
c) Concave meniscus and convex meniscus

5. Give reason.
a) Meter is called a standard unit.
b) SI Unit brings uniformity in measurement throughout the world.

6. Answer the questions with the help of the given figure.
a) Calculate the area of the irregular object shown in the
given figure. (Area of 1 smallest unit = 1 cm2)
b) Find the diameter of the sphere shown in the given figure.

c) The measuring cylinders shown in the figure are filled with equal amounts
of water.

i) Write down the reading of the
measuring cylinder that contains

a. Water and pebble rubber

b. Water and rubber pebble

c. Water, pebble and rubber

ii) Find the volume of rubber and pebble.

d) Write the name and advantage of the instrument shown
in the figure.

18 Measurement

STEP 3

7. Answer the following
a) Define
i) mass ii) length iii) time
iv) area v) volume vi) standard one meter
vii) standard one kilogram viii) second
b) What is meant by measurement?
c) Write the importance of measurement in daily life.
d) What is a physical quantity? Give four examples.
e) What are fundamental quantities? Give four examples.
f) What is a standard unit? Give three examples.
g) What are the characteristics of a standard unit?
h) What is SI Units? Write why it is needed.
i) List the fundamental quantities along with their SI Units.
j) Explain the method to measure the external diameter of a sphere.
k) Write the relationship between the quantity of matter and the mass of
object.
l) How is the area of a regular plane surface calculated? Write with an
example.
m) How is the area of an irregular plane surface calculated?
n) How is the volume of a regular object calculated? Write with an example.
o) How is the volume of irregular objects calculated?
p) Write the things to remember while measuring the volume with the help
of a measuring cylinder.

8. Numerical problems
a) If the radius of a coin is 1cm then calculate its area.
b) Calculate the volume of a ball having a radius of 8 cm.
c) Length, breadth and height of a room are 5m, 4m and 4m respectively.
Calculate area and volume.

9. Draw the diagram
a) to show concave meniscus and convex meniscus.
b) to show the measurement of volume of an irregular object with the help of
a measuring cylinder.

UNIT Estimated teaching periods TheoMryoderPnraCcotniccaepl t Science and Environment - 7 19
51
2
Force and Motion

Syllabus issued by CDC Moving car

 Types of force
 Distance and displacement
 Scalar and vector quantities
 Speed and velocity
 Acceleration

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 explain various types of force.
 introduce distance and displacement.
 define speed and velocity and explain uniform and non-uniform velocity.
 define acceleration.
 solve simple numerical problems related to force and motion.

Key terms and terminologies of the unit

1. Force: The push or pull that changes or tends to change the state of an
object from rest to motion or from motion to rest is called a force.

2. Contact forces: Some forces act only if they have physical contact with the body.
Such forces are called contact forces.

3. Non-contact forces: The forces developed without contact between the bodies are
called non-contact forces.

4. Muscular force: The force resulting due to the action of muscles is known as the
muscular force.

5. Centripetal force: The force acting on a body moving along a circular path and
directed towards the center of the circular path is called a
centripetal force.

6. Centrifugal force: A pseudo force developed on a body in circular motion which
appears to be pushing the body away from the center of the
circular path is called a centrifugal force.

20 Force and Motion

7. Gravitational force: The force of attraction between any two objects because of
their masses is called a gravitational force.

8. Gravity: The force with which any planet or satellite attracts objects
towards its center is called the gravity.

9. Magnetic force: The force exerted by a magnet is called a magnetic force.

10. Electrostatic force: The force exerted by a charged body on another charged or
uncharged body is called an electrostatic force.

11. Frictional force: The force which opposes the relative motion between two
bodies in contact is called a frictional force.

12. Scalar quantity: A physical quantity which is described completely by its
magnitude only is called a scalar quantity.

13. Vector quantity: A physical quantity which requires both magnitude and
direction for its complete description is called a vector quantity.

14. Distance travelled: The actual length of the path travelled (or covered) by
a moving body, irrespective of its direction is called the
distance travelled by the body.

15. Displacement: The shortest distance between the initial position and the
final position of a moving body in a particular direction is
called its displacement.

16. Speed: The distance travelled by a body per unit time is called speed.

17. Velocity: The distance travelled by a body per unit time in a particular
direction is called its velocity.

18. Uniform-velocity: A body is said to have a uniform velocity when it travels in
a particular direction and covers equal distances in equal
intervals of time.

19. Non-uniform velocity: A body is said to have a non-uniform velocity when it travels
in a particular direction and covers unequal distances in
equal intervals of time.

20. Average velocity: If the velocity of a body in a particular direction changes
continuously at a uniform rate, then the arithmetic mean of
the initial velocity and final velocity over a given period of
time is called the average velocity.

21. Acceleration: The rate of change of velocity of a body with respect to time
is called its acceleration.

22. Retardation: The rate of decrease in velocity is called retardation or
negative acceleration.

Modern Concept Science and Environment - 7 21

2.1 Introduction

In our surroundings, some objects do not change MEMORY PLUS

their position but the others do so. A body which Rest and motion are relative terms.

does not change its position with respect to its

surroundings is said to be at a state of rest. For example, buildings and plants are in a

state of rest. A body which changes its position with respect to its surroundings is said

to be in a state of motion. For example, a football kicked by the foot, a falling apple,

etc. are in a state of motion. An external force is necessary to change the state of a body

from rest to motion and vice versa. In this unit, we will learn about the different types

of forces. We will also learn about speed, velocity and acceleration.

2.2 Force

We have observed that a rolling football on the ground slows
down after some time. A football player kicks a rolling football
to change its direction. What makes the ball slow down and
change its direction of motion? There is an external agent, i.e.
the force, which causes this. Thus, the external factor which
changes or tends to change the state of an object from rest to
motion or from motion to rest is called a force.

1. SI Unit of Force : The S.I. Unit of Force is newton (N). Playing football

2. C.G.S. Unit of force : The C.G.S. Unit of Force is dyne.

1N = 1,00,000 dyne MEMORY PLUS
Force is a derived quantity.
3. Effects of Force

i) Force can change the direction of a body.

ii) Force can change the shape and size of a body.

iii) Force can change the state of a body.

iv) Force can change the speed of a moving body.

FACT WITH REASON

Why does a brick break on hammering?
A brick break on hammering because force can change shape, size and structure of a body.

4. Force in our life : It is not possible to live on the earth without the application
of force. In our daily life, force is essential for us to perform different types of
work. We use muscular efforts while pushing, pulling or changing the shape of
objects. Both human body and machine need force to perform any type of work.
For example, we need force to walk and carry load. Cricket players exert a force
to throw a ball.

22 Force and Motion

5. Force – A Push or a Pull : While doing different

types of work, the force applied is meant to either

pull, push or do both. Examples:
a) Force is applied to pull a bucket of water

from the well.

b) Animals such as a horse, ox, camel, etc. Pulling a box
apply force to pull a cart.

c) We pull and push the door in order to open or close it.

d) To move a book on a table, we can pull as well as push it.

Thus, a force is a push or a pull on an object.

Types of Force

Some forces act only if they have physical contact with the body. Such forces are called
contact forces. Muscular force, frictional force, a push or a pull are contact forces. The
forces developed without contact between the bodies are called non-contact forces.
Magnetic force, gravitational force and electrostatic force are non-contact forces.

FACT WITH REASON

Gravitational force is a non-contact force. Why?
Gravitational force is a non-contact force because this force exists even without two objects
touching each other.

Differences between Contact Forces and Non-contact forces.

Contact Forces Non-contact Forces

1. Contact forces arise due to the 1. Non-contact forces arise due to

contact between two different attraction or repulsion between two

objects. objects even as there is no contact

between the objects.

2. There is no field associated with 2. There is always a field associated

a contact force such as muscular with a non-contact force, such as

force, frictional force and up-thrust. gravitational force, electrostatic

force and magnetic force.

Muscular Force

Our muscles contract and relax while performing

different activities. The force resulting due to the action

of muscles is known as the muscular force. This force

enables us to perform all activities including, walking, Muscular force
running, swimming, pulling, pushing, lifting, climbing,

etc. Ox, horse and camel also use their muscular forces to pull carts.

Modern Concept Science and Environment - 7 23

FACT WITH REASON

The muscular force is a contact force. Why?
Muscular force can be applied only when it is in contact with an object. So the muscular force
is called a contact force.

Centripetal Force and Centrifugal Force

ACTIVITY 1

i) Take a rubber ball and tie it tightly with a string of length about 1.5m.
ii) Rotate the ball in a circular path. Do you apply a force from hand to rotate the ball

in the circular path? Do you feel a force acting on the ball which tries to pull out
the ball from your hand?
Explanation: In this activity, the force applied from the hand is the necessary centripetal
force and the force which pulls the ball outward is the centrifugal force. If the thread
is released suddenly, the ball flies away from the center due to the centrifugal force.

Centripetal Force

When a body is moving MEMORY PLUS
uniformly along a circular Moon revolves around the earth
path, the magnitude of its due to centripetal force.

velocity remains constant, but the direction of the velocity

changes continuously. Such change in direction is due to the

force acting perpendicularly to the direction of the velocity.

The force acting on a body moving along a circular path

which is directed towards the center of the circular path is Centripetal force

called a centripetal force. For example, a cyclist taking a turn on a circular path, a

satellite revolving in a circular orbit and a person riding the ferries wheel experience

the centripetal force.

FACT WITH REASON

Why does not earth escape away from the sun?

Earth does not escape away from sun because of the gravitational force and centripetal force
acting on it.

Centrifugal Force Orbit
Axis
MEMORY PLUS

A body in circular motion appears Centrifugal force is an apparent force.
to be pushing outward due to a
Centripetal

force called centrifugal force. Thus, the pseudo force developed on a force

body in circular motion which appears to be pushing the body away Velocity
Centrifugal force

24 Force and Motion

from the center of the circular path is called a centrifugal force. For example, clothes
in a running washing machine and mixture in centrifuge experience the centrifugal
force. The centripetal force and centrifugal force are equal in magnitude but opposite
in direction.

Thus, when an object moves in a circular motion, it experiences two types of forces
simultaneously. One is the centripetal force which acts towards the center and the other
is the centrifugal force which acts away from the center. An object moves in a circular
path, whenever there is a balance between the centripetal force and centrifugal force.

Centripetal Force Centrifugal Force

1. Centripetal force is always directed 1. Centrifugal force is always directed

towards the center. away from the center.

2. It is the cause of a circular motion. 2. It is the effect of circular motion.

3. It is a real force. 3. It is a pseudo force.

FACT WITH REASON

Why does not earth fall inside the sun?
Earth does not fall inside the sun because of the balanced centripetal and centrifugal forces.

Gravitational force MEMORY PLUS
Tides occur in the ocean due to
Planets revolve around the sun gravitational force of the moon.
due to a mutual force of attraction

between them. This mutual force is called gravitational force.

Thus, the force of attraction between any two objects because of

their masses is called a gravitational force. For example, Gravitational force

i) The earth and the moon attract each other.

ii) The sun and the earth also attract each other.

Gravity

When a ball is thrown up from the surface of the earth, it falls

back on the earth. It is due to force of gravity. The force with

which any planet or satellite attracts objects towards its center is

called gravity. The force of gravity on a body is also known as

the weight of the body.

FACT WITH REASON An apple falling from tree

Why an apple always falls? It does not fly away.
An apple always falls downward. It does not fly away because it is pulled by the gravity of earth.

Modern Concept Science and Environment - 7 25

Effects of Gravity
a) An object thrown upward falls back on the surface of the earth.

b) Rain, snow and hailstone fall on the earth.

c) Rivers flow from higher to lower altitudes.

Magnetic Force

Magnet attracts magnetic substances like nickel, cobalt, etc. with the force called
magnetic force. Thus, the force exerted by a magnet is called a magnetic force.

ACTIVITY 2

I) Take a pair of bar magnets and place one over three cylindrical pencils on a table.
ii) Bring one end of another magnet close to the pole of another magnet. Do the pencils

roll when the magnet experiences some force?
iii) Repeat the process for the next pole of the bar magnet in hand. Do you observe the

movement in the opposite direction?
Explanation: Like poles of the bar magnets repel and the magnet on the pencils gets pushed.
Whereas the magnet gets attracted when an unlike pole is brought closer.

Natures of Magnetic Force
a) Attractive Force of Magnet : An attractive force develops when the North Pole

of a magnet is brought nearer to the South Pole of another magnet.
b) Repulsive Force of Magnet : A repulsive force develops when the North Pole

of a magnet is brought nearer to the North Pole of another magnet.

S Thread NN S
NN S Attractive S
Magnet Repulsive
force force
N
S N
S

Repulsive and attractive force of magnet

FACT WITH REASON

The force exerted by a magnet is a non-contact force. Why?
A magnet can exert a force on another magnet or magnetic substances without being in
contact with it. So, the force exerted by a magnet is a non-contact force.

Magnetic Field

The region surrounding a magnet, where another magnet or magnetic substance,
experiences a force is called the magnetic field.

26 Force and Motion

Advantages of Magnetic Force
i) Magnetic force is used to displace heavy iron objects from one place to another

in factories.

ii) Magnetic force is used to separate magnetic substances from a mixture.

Electrostatic Force

When an electric charge is placed near another electric charge, it experiences a force of
attraction or repulsion. There is a force of attraction between two unlike charges and
a repulsive force between two like charges. Thus, the force exerted by a charged body
on another charged or uncharged body is called an electrostatic force. For example,

i) A comb rubbed with hair pulls paper pieces around it due to an electrostatic force.

ii) An electron revolving round the nucleus changes its direction continuously due
to the electrostatic force between nucleus and the electron.

Comb before rubbing Comb after rubbing
No attraction Attraction
Pieces of paper Pieces of paper

No electrostatic force Electrostatic force

Electric Field

The region surrounding an electric charge, where another electric charge, positive or
negative, experiences a force is called the electric field.

Static Electricity MEMORY PLUS
Human body is also a good
The charge developed on non-metallic substances conductor of electric charge.
such as plastics, rubbers, wool and polyester due
to friction is called a static electricity. For example,

when a comb is rubbed with hair, a positive charge develops on the hair and a negative

charge on the comb.

FACT WITH REASON

An electrostatic force is a non-contact force, why?
An electrostatic force comes into action to affect the state of objects even when they are not
in direct contact. So, it is called a non-contact force.

ACTIVITY 3

i) Rub an air-filled balloon with hair.
ii) Bring it near a wall. Does the balloon stick with the wall?

Modern Concept Science and Environment - 7 27

FACT WITH REASON

The air-filled balloon rubbed with hairs sticks to the wall. Why?
When a balloon is rubbed with hairs, it becomes negatively charged. The negatively charged
balloon brought close to a wall induces a positive charge on the wall. So the air-filled balloon
tends to stick to the wall.

Frictional force MEMORY PLUS

When a football is kicked to roll it on the ground, The frictional force always acts in a
it gradually slows down and finally stops at some direction opposite to the motion.

distance. This happens due to the opposing forces that are at work between the ground

and the football. Such an opposing force is called a frictional force. Hence, the force

which opposes the relative motion between two bodies in contact is called a frictional

force. Origin of the frictional force lies in the interlocking of uneven projections of

two surfaces. Thus, smoother surfaces have less friction and vice versa.

FACT WITH REASON

How are we able to walk?
We are able to walk because of frictional force between our sole and ground.

Advantages of Frictional Force

Even though friction irritates us, it plays a great role in our daily life. Friction makes it
possible to hold objects, to write or to walk, etc. So, friction is also called a necessary evil.

a) When brakes are applied on a bicycle, a frictional force between the brake pads
and bicycle wheel brings the bicycle to a halt.

b) It is possible to walk on the ground because of friction on the ground. Friction
saves us from slipping on a rough surface better than on a smooth surface. If the
surface on which we walk is perfectly smooth, we will tend to skid and will be
unable to walk.

c) It is possible to write with pen or pencil due to friction.

FACT WITH REASON

An ink pen does not write on an oily paper. Why?
Oil on the surface of an oily paper reduces the friction between the nib of the pen and paper,
which is essential to write on the paper. So ink pen does not write on an oily paper.

d) The friction between the lateral surface of a match box and the head of the match
stick produces heat. It enables us to light the match stick.

e) Friction makes it possible to hold an object in our hand.

28 Force and Motion

f) It is possible to ride a motorbike due to the friction between the tyres and the
road. If the road is slippery, the motorbike would slip making it hard for us to
ride the bike.

Disadvantages of Friction

a) Friction Opposes Motion : A body in motion would never stop if there were no
friction. It is the friction which stops a bicycle after some time when we stop paddling.

b) Friction Causes Wear and Tear
a) When we walk with shoes on our feet, the friction between the shoes and
the ground causes the soles to wear out.

b) Friction causes the wear and tear of machine parts and this leads to the
damage of certain machineries.

c) Friction Produces Heat : In winter, we rub our palms together to warm up
our hands. Similarly, heat generated due to friction in machines causes much
wastage of energy.

FACT WITH REASON

When two dry woods are rubbed, it starts to burn. Why?
When two dry woods are rubbed, it starts to burn because of heat produced due to friction.

Methods to Increase Friction Spikes
Grooves
Friction is desirable in some cases and we
want to increase it by different methods.
For example,

a) Sole of shoes is grooved to provide Tyre
the shoes better grip on the floor. Footballers shoes

b) The tyres of cars, trucks and bulldozers are grooved to provide better grip with
the ground.

c) Brake pads are used in the brake systems of bicycles, motorcycles and automobiles
to control their speed.

d) Wheel driving belts of machines are made up of special materials to increase the
friction.

Methods to Decrease Friction

In some situations, friction is undesirable and we minimize it by different methods.
For example,

1. Stream-lined Shape : The idea of streamlined shapes has been taken from the
birds flying in the air. Automobile, airplanes and ships are especially designed
into stream-lined shapes to reduce friction. Fishes also have stream-lined bodies.

Modern Concept Science and Environment - 7 29

FACT WITH REASON

Why do birds have a boat shaped body?
Birds have a boat shaped body to reduce friction with air while flying.
When the airplane is in the air, its wheels are folded inside its body. Why?
When wheels are folded inside the body, the plane gets streamline shape. As a result, it reduce
friction in the air. The birds do the same with their feet while flying and landing.

2. Rolling Instead of Sliding : Rolling friction is smaller than sliding friction.
Thus, the sliding parts in a machine are fitted with ball bearings.

3. Polishing of Rough Surface : Rough surfaces are polished to reduce friction.
For example, carom board is highly polished to reduce friction with carom
striker and other coins.

4. Oiling : A few drops of oil are poured on the hinges of a door to move it smoothly.
5. Greasing : Grease is used in the moving parts of bicycles and machines to

reduce friction.

Lubricants

The substances which reduce friction are called lubricants. Lubricants can be in solid,
liquid or gaseous forms.

a) Solid lubricants: Examples are graphite powder, boric powder, talcum powder, etc.

b) Liquid lubricants: Examples are oil, ghee, etc. MEMORY PLUS
c) Gaseous lubricants: Examples are air, oxygen, etc. Oils are added to the engine of a
vehicle to reduce frictional force.
FACT WITH REASON

A luggage with wheels underneath is easier to pull. Why?
The friction on rolling wheels is less than that on the luggage without the wheels. So, luggages are
provided with wheels.

Boric powder is sprayed on carom board. Why?
Boric powder reduces the friction between the board and the carom striker and coins. So, boric
powder is sprayed on carom board.

Friction cannot be reduced to zero. Why?
No surface is perfectly smooth. Some irregularities are always there. By polishing surfaces or by
using a large amount of lubricants, friction can be reduced, but it can never be zero.
Why do we slip on a clean marble floor?
We slip on a clean marble floor because marble floor is smooth that decreases friction.

30 Force and Motion

ACTIVITY 4

i) Take a thick book and slide it on a table.
ii) Now, take four cylindrical pencils and place them parallel to one another on the table.
iii) Place a thick book over the pencils and push the book. Do you feel it easier to

push the book in this case?
When the pencils roll on the table, the friction decreases and it becomes easier to push
the book.

2.3 Scalar and Vector Quantities

Scalar Quantity

A physical quantity which is described completely by its magnitude only is called a
scalar quantity. For example, distance, speed, mass, etc. A scalar quantity has only
magnitude and no direction.

FACT WITH REASON

Why is mass a scalar quantity?
Mass is a scalar quantity because it has magnitude but no direction.

Vector Quantity

A physical quantity which requires both magnitude and direction for its complete
description is called a vector quantity. For example, displacement, force, weight,
velocity, etc. A vector quantity has both magnitude and direction.

FACT WITH REASON

Why is weight a vector quantity?
Weight is a vector quantity because it has magnitude and direction as well.

Differences between Vectors and Scalars

Vectors Scalars

1. Vectors have both magnitude and 1. Scalars have only magnitude.
direction.

2. The sum of vectors may be zero, 2. The sum of scalars is always a

positive and negative. positive number.

3. We can add or subtract vectors with 3. We can add or subtract scalars with

the rules of vector algebra. the rules of simple algebra.

Modern Concept Science and Environment - 7 31

2.4 Distance and Displacement

Distance

The actual length of the path that is covered by a moving body, irrespective of its

direction is called the distance. It is a scalar quantity. A 8 cm D

For example, when a man travels 8m from point B to point C,

4m from point C to point D and then 8m from point D to point 4 cm 4 cm
A, then the total length of the path travelled by the man

= BC + CD + DA B 8 cm C

or, Distance = 8m + 4m + 8m = 20m

The SI unit of distance is meter (m). MEMORY PLUS
When a man travels from a point
Displacement A to another point B towards a
particular direction and return back
The shortest distance between the initial position and to A from the same path, the net
the final position of a moving body in a particular displacement is zero.
direction is called its displacement. It is a vector
quantity.

For example, when a man travels from a point B to another point A towards a particular
direction, then the displacement of the man, BA = 4m in that direction.

Differences between Distance and Displacement

Distance Displacement

1. Distance is the actual length of the path 1. Displacement is the shortest distance

travelled by a body in motion. between two positions of a body in

motion.

2. Distance is a scalar quantity. It is always 2. Displacement is a vector quantity. It can

positive. be positive, negative or zero.

2.5 Speed and Velocity

Speed

Whenever we try to find out which of the two or more vehicles is moving faster, then

we compare the distances covered by them in a unit time. If we know the distance

travelled by two cars in a minute then we can tell which car is moving faster. The

distance travelled per unit time is called speed. MEMORY PLUS
Speed = Distance travelled Speed is measured by a speedometer.

Time taken

32 Force and Motion

It is a scalar quantity. In CGS system, the unit of speed is centimeter per second, which
is written as cm/s. In SI Units, the unit of speed is meter per second, written as m/s.
The speed of fast moving bodies such as cars and buses are expressed in kilometer per
hour, written as km/h.

When the speedometer of a car indicates 72km/h, it implies that, if the speed remains
the same, the car will cover a distance of 72 kilometers in one hour. In practice,
however, the speed of the car may not remain constant for one hour.

FACT WITH REASON

Speed is a scalar quantity. Why?
Speed of a body has only magnitude but no direction. So, speed is a scalar quantity.

Velocity

Velocity is a physical quantity which has both direction of motion and the distance
travelled. So, the distance travelled by a body per unit time in a particular direction is
called velocity. If a body covers a distance of ‘s’ in time ‘t’ in a specific direction, then
its velocity ‘v’ is given by

v = Distance travelled in a particular direction = s MEMORY PLUS
Time taken t
The displacement travelled by
It is a vector quantity. The unit of velocity is the same
a body per unit time is called
as that of speed. i.e. In SI system, the unit of velocity
velocity.

is m/s.

FACT WITH REASON

Velocity is a vector quantity. Why?
Velocity has both magnitude and direction. So, it is a vector quantity.
Velocity can be negative. Why?
Velocity can be negative because it is a vector quantity. The sum of vectors may be negative,
positive or zero.

Solved Numerical 2.1

Find the speed of a car which covers 800 meters in 40 seconds.
Solution: Given,
Distance covered by car = 800 m
Time taken = 40 s

Modern Concept Science and Environment - 7 33

According to formula,

Speed = Distance travelled = 800 =20 m/s
Time taken 40

The speed of the car is 20m/s.

Differences between Speed and Velocity

Speed Velocity

1. Speed is the distance travelled by a 1. Velocity is the displacement travelled

body per unit time. by a body per unit time.

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

2.6 Uniform Velocity and Non-uniform Velocity

Uniform Velocity MEMORY PLUS
Velocity of planets, satellites, etc. is
A body is said to have a uniform velocity when it the uniform velocity.
travels in a particular direction and covers equal

distances in equal intervals of time. For example, if a car is moving along a straight

road towards east such that in every one second it covers a distance of 12m, the

uniform velocity of the car is 12m/s east.

12m 12m 12m 12m

0s 1s 2s 3s 4s

Non-uniform Velocity (Variable Velocity) MEMORY PLUS
When a car moves in a circular
A body is said to have a non-uniform velocity when track, covering equal distances in
it travels in a particular direction and covers unequal equal interval of time, its direction
distances in equal intervals of time. For example, a of movement is changing. Hence,
body starts from point A and reaches B, C, D and in a circular path, the car will have
E, towards east as shown in the given figure. In this changing velocities.
case the body is moving with a non-uniform velocity.

8m 1s 20m 10m 22m
0s 2s 3s 4s

Average Velocity

If the velocity of a body in a particular direction changes continuously at a uniform
rate, then the arithmetic mean of the initial velocity and final velocity over a given
period of time is called an average velocity.

34 Force and Motion

Average velocity (vav) = Initial velocity (u) + final velocity (v)
or, Average velocity (v) = Total displacement 2
1s 1s
Total time taken 1s 1s East
4m
In the given figure alongside, 3m 4m 2m

AB CD E

Total displacement (s) = 3m +4m + 2m + 4m = 13m

Total time (t) = 4s
Average velocity = Total displacement = 13 = 3 .25 m/s east
Solved Numerical 2.2 Total time taken 4

Calculate the average velocity of a bus which is displaced by 7500m in 5minutes.
Solution: Given,

The total distance travelled = 7500m

Total time taken = 5 minutes = 5 × 60 seconds = 300s

From the formula,
Average velocity = Total displacement = 7500 = 25 m/s

Total time taken 300
The average velocity of the bus is 25m/s.

2.7 Acceleration

Objects in motion may not have a uniform velocity. For example, a bus starts from rest
and, after a certain time, it attains a constant velocity. If a person appears on the road
in front of the bus, the driver applies brakes and the velocity gradually decreases.
Finally the velocity of the bus becomes zero when it stops. Thus, the rate of change of
velocity of a body with respect to time is called its acceleration.

i.e. Acceleration (a) = final velocity (v) – initial velocity (u)
time taken (t)
or, a = v – u
t 2 m/s 4 m/s 6 m/s 8 m/s

The SI unit of acceleration is meter per square Force 1s 1s 1s East

second written as m/s2.

For example, in the given figure alongside AB C D

Average velocity = final velocity (v) – initial velocity (u)
time taken (t)

or, a = 8 m/s – 2 m/s = 6 m/s = 2 m/s2
3s 3s

Modern Concept Science and Environment - 7 35

Meaning of Acceleration MEMORY PLUS
The negative acceleration is called
An acceleration of 2m/s2 means that the velocity retardation.
increases by 2m/s every second.

FACT WITH REASON

Acceleration of a body in uniform motion is zero. Why?
Acceleration of a body in uniform motion is zero because there is no change in velocity, i.e. v= u.

Solved Numerical 2.3

A car moving with the speed of 15m/s speeds up to 30m/s in 5s. Calculate its
acceleration.

Solution: Given,

The total time taken = 5s MEMORY PLUS
1. For an object starting from rest,
Initial velocity of the car (u) = 15m/s the initial velocity (u) = 0

Final velocity of the car (v) = 30m/s For an object coming to rest from
motion, the final velocity (v) = 0
From formula,
Acceleration = v – u = 30 – 15 = 3 m/s2 2. Acceleration due to gravity of
a freely falling object towards the
t5 earth surface is 9.8m/s2.
Acceleration of the car is 3 m/s2.

Negative acceleration (Retardation)

If the final velocity (v) of a moving body is less than the initial velocity (u), i.e. v < u then,

Acceleration = final velocity – initial velocity = Negative quantity
time taken time

= Negative quantity

The decrease in velocity of a body with time causes a negative acceleration. The rate
of decrease in velocity is called a negative acceleration. Negative acceleration is also
called retardation. For example, a ball we throw up has a negative acceleration until it
reaches the top point and returns. A football rolling on the ground also has a negative
acceleration.

FACT WITH REASON

A ball thrown upward from the earth has a retardation. Why?
If a ball is thrown up, its velocity decreases until it reaches the maximum height and then returns.
As the final velocity before the ball returns is zero, which is less than the initial velocity, the
acceleration is negative. So, a ball thrown upward from the earth has a retardation.

36 Force and Motion

STEPS EXERCISE

STEP 1

1. Tick () the correct statement and cross () the incorrect one.
a) An object thrown upward from the earth’s surface falls on the ground due
to gravity.
b) Burning of a meteor in the atmosphere is due to the gravitational force.
c) Rolling friction is less than the sliding friction.
d) Mass is a vector quantity.
e) Airplanes are streamlined to reduce friction.
f) Velocity has both magnitude and direction.
g) When a body covers equal distances in equal intervals of time in a specified
direction, it is said to be moving with a uniform speed.

2. Fill in the blanks with appropriate words
a) The SI Unit of force is …… .
b) Weight is a …… quantity.
c) Use of fine powder on a carom board ……. friction.
d) Shape of an aeroplane is ……. to reduce friction with air.
e) Friction depends on the ……. of two surfaces in contact.
f) Oil is applied to machines to . ……friction.
g) Speed has …… but no direction.

STEP 2

3. Answer in one word
a) What is the unit of force in the cgs system?
b) What develops a magnetic force?
c) Which type of electricity is developed from friction?
d) What is the term for the total distance travelled by a body per unit time?
e) What is the term for the rate of change of velocity?
f) Which force is known as a necessary evil?
g) What is the term for the rate of decrease of velocity of a body?

4. Differentiate between:
a) contact force and non-contact force
b) centripetal force and centrifugal force
c) scalar quantity and vector quantity
d) distance and displacement

Modern Concept Science and Environment - 7 37

e) speed and velocity
f) uniform velocity and non-uniform velocity
g) acceleration and retardation

5. Give reasons.
a) The muscular force is called a contact force.
b) A bicycle stops on applying brakes on it.
c) Speed is a scalar quantity.
d) Velocity is a vector quantity.
e) An object thrown up in the sky falls back on the earth’s surface.
f) Friction is a necessary evil.
g) Airplanes and ships have streamlined shapes.

6. Answer the questions with the help of the given figures
a) Write the type of force shown in the given figures.

Comb NN S
S
Attraction Attractive
Pieces of paper force N
S
i) ii) iii)
b) Mention the effect of frictional force in the given figure. iv)

c) Write what increases/decreases the frictional force in the
figures.

Lift

i) ii) iii) iv)

STEP 3

7. Answer the following questions.
a) What is force? Why is force needed?
b) Define the following terms, with an example for each.
i) muscular force ii) gravitational force
iii) gravity iv) magnetic force
v) electrostatic force vi) frictional force

38 Force and Motion

c) Define.
i) velocity ii) average velocity
iii) acceleration iv) retardation

d) Write the SI Unit of the following.
i) displacement ii) speed
iii) velocity iv) acceleration

e) What are the effects due to gravity?
f) Write about the nature of the magnetic force.
g) What are the applications of the magnetic force?
h) List the advantages of the frictional force.
i) Write about two disadvantages of the frictional force.
j) What are the methods to increase friction?
k) What are the methods to decrease friction?
l) What are lubricants? Give examples.
m) What is velocity? How is it calculated? Write the SI Unit of velocity.
n) How is the average velocity calculated?
o) What is the formula to calculate acceleration?
p) A body in motion has an acceleration of 2m/s2. What does this mean?

8. Numerical problems

a) A car travels a distance of 800m in 40s. Calculate its speed. [Ans:20m/s]

b) In a 100m race, the winner takes 10s to reach the finishing point. Calculate

the velocity of the winner. [Ans:10m/s]

c) A car is moving with a speed of 25m/s. Calculate the distance travelled by

the car in 30 seconds. [Ans:750m]

d) A car is moving with a speed of 20m/s .Calculate the distance travelled by

the car in 1 minute. [Ans:1200m]

e) A bus travels a distance of 7500m in 5 minutes. Calculate its average

velocity. [Ans:25m/s]

f) The velocity of a car moving with 20m/s becomes 30m/s after 5s. Calculate

its acceleration. [Ans:2m/s2]

g) A car starts from rest and its velocity becomes 30m/s after 5s. Calculate its

acceleration. [Ans: 6m/s2]

9. Draw the diagram
a) to show the effects of the following forces:
i) gravitational force ii) frictional force
iii) centripetal force iv) magnetic force
b) to show the forces acting on the earth revolving around the sun in its orbit.

UNIT Estimated teaching periods TheoMryoderPnrCacotnicceapl t Science and Environment - 7 39
31
3
Simple Machine

Syllabus issued by CDC Scissors

 Introduction to simple machines
 Types of simple machines (lever, pulley, wheel and axle, inclined plane, screw

and wedge)
 Types of lever
 Utilities of simple machines
 Importance of simple machines

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 identify various types of simple machines (lever, pulley, wheel and axle, inclined

plane, screw and wedge) and define each of them.
 explain the utilities of simple machines and utilize them in their daily life.

Key terms and terminologies of the unit

1. Simple machine: Simple machine is a device that makes our work easier,
faster and more convenient.

2. Complex machine: Complex or a compound machine is a type of machine that
has two or more simple machines working together in it.

3. Load: Load is the resistance to be overcome or weight being lifted
by a simple machine.

4. Load distance: The distance moved by load in a simple machine is called
the load distance.

5. Effort: Effort is the force applied directly to a simple machine to
move the load or to do work.

6. Effort distance: The distance moved by effort applied in a simple machine is
called the effort distance.

7. Mechanical advantage: The ratio of the load lifted to the effort applied in a simple
machine is called the mechanical advantage.

8. Velocity ratio: The ratio of the distance moved by effort to the distance
moved by load in a simple machine is called the velocity ratio.

40 Simple Machine

9. Input work: Work done on a simple machine by a given effort is called the
input work.

10. Output work: Work done by a simple machine on the load is called the
output work.

11. Efficiency: The percentage ratio of output work to input work in a simple
machine is called the efficiency.

12. Real machine: The machine used in our daily life is called a real or practical
machine.

13. Perfect simple machine: A hypothetical frictionless machine, in which the total input
work is converted into output work without a wastage of
energy is called an ideal or a perfect simple machine.

14. Fulcrum: Fulcrum is the fixed axis around which a lever or a rigid bar
can rotate.

15. Lever : A lever is a rigid bar which is capable of rotating about a fixed
axis called the fulcrum.

15. Principle of lever: The principle of lever states that, “when a lever is in a condition
of equilibrium, the product of the effort and the effort arm is
equal to the product of the load and the load arm.”

16. Pulley: The metallic or wooden circular disc having a groove along its
rim and capable of rotating about an axis passing through its
center is called a pulley.

17. Single fixed pulley: A pulley which does not move up and down with load is called
a single fixed pulley.

18. Single movable pulley: A pulley which moves up and down with load is called a
single movable pulley.

19. Block and tackle: A combination of pulleys is called block and the arrangement
of pairs of blocks consisting of one or more pulleys is called a
block and tackle system.

20. Wheel and axle: A system of two co-axial cylinders of different diameters,
which rotate together is called the wheel and axle.

21. Inclined plane: An inclined plane is a flat solid surface, placed in a way to
form a slope, with one of its ends higher than the other, so that
it can provide support in raising or lowering a load.

22. Screw: A metallic rod with an inclined plane in the form of spiral
threads around it is called a screw.

23. Wedge: A wedge is a triangular metallic or wooden piece, formed by
combining two inclined planes.

Modern Concept Science and Environment - 7 41

3.1 Introduction

In our daily life, we use a variety of tools that make our work easy. For example,
sharp objects are used for cutting things, pulleys are used to lift loads, wheel and axle
multiply our effort or speed up our work, slanted surface is used to multiply effort,
etc. Such devices give us an advantage by changing the amount, speed, or direction
of forces. The device, which makes our work easier, faster and more convenient is
called a simple machine. For example, scissor, knife, nut cracker, bottle opener, spoon,
pulley, screw etc. These machines need muscular energy to do the work.

Bottle opener Knife Nail cutter

Pulley

Screwdriver Wheelbarrow scissors

Most of the machines we use nowadays are compound in structure. Complex or a
compound machine is a type of machine that has two or more simple machines
working together in it. For example, clocks, bicycle, motor bike, sewing machine etc.
Compound machines use different types of energy like electrical energy, chemical
energy etc. to work.

In this unit, we will learn about the different types MEMORY PLUS
No simple machine is 100% efficient.
of simple machines and their applications.

3.2 Advantages of Using Simple Machines

A simple machine enables us to
1. A simple machine helps us to multiply the force applied.
2. A simple machine helps us to perform our work faster.
3. A simple machine helps us to change the direction of the applied force.
4. A simple machine helps us to transfer force from one place to another.

FACT WITH REASON

We use simple machines in our daily life. Why?
We use simple machines in our daily life because they make our work easier, faster and convenient.

42 Simple Machine

3.3 Types of Simple Machine

i) Lever ii) Pulley iii) Wheel and axle

iv) Inclined plane v) Screw vi) Wedge

Lever

A lever is a rigid bar which is capable of rotating about a fixed axis called the fulcrum.
For example, crowbar, wheelbarrow, scissors, spoon etc.

General Terms Used in the Study of Lever Effort
a) Fulcrum : The fixed point about which a

Load

lever rotates is called the fulcrum.

b) Load : The weight to be lifted by using a Load distance Effort distance

lever is called load (L). Fulcrum

c) Effort : The force applied on lever to lift a Lever

e) load is called effort (E). MEMORY PLUS
Load distance : The distance of the load from the (a) When the effort distance is longer

fulcrum is called the load distance or load arm. than the load distance, i.e. effort

distance > load distance, the

f) Effort distance : The distance from the fulcrum effort gets multiplied.

at which an effort is applied is called the effort (b) When the load distance is longer
than the effort distance, i.e. load
distance or effort arm.
distance > effort distance, work
g) Principle of Lever : The principle of lever becomes faster.
states that, “when a lever is in a condition of

equilibrium, the product of the effort and effort arm is equal to the product of

the load and load arm.”

i.e. in an equilibrium condition,

effort (E) × effort arm (Ed) = load (L) × load arm (Ld)

Types of Lever

On the basis of the position of load, effort and fulcrum, levers are grouped into three types.

i) First class lever

A lever with load and effort on either side of the fulcrum is called the first class lever.
For example, DHIKI, scissors, beam balance, crowbar, wire cutter, pliers etc. The effort
arm and load arm depend on the position of the fulcrum between them. Generally, the
effort arm is made longer than the load arm in the first class lever to multiply the effort.

Crowbar See-saw Scissors Pliers Nail cutter

First class lever