Oasis Science and Technology 9

Based on New Curriculum

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

Oasis

9Grade

Editor Author
Dr. Rameshwar Adhikari Jayananda Kapadi

Reader M.Sc. (Zoology), B.Ed. (Health Education)
Tribhuvan University, Kirtipur, Kathmandu
Central Department of Chemistry

Tribhuvan University, Kirtipur, Kathmandu

Oasis

9Grade

Publisher and Distributor:

Oasis Publication Pvt. Ltd.

Tel: 014224004, Fax: 4227718

Author:
Jayananda Kapadi

Language Editors:
Ramesh Lamsal
Bhan Dev Kapadi

Edition: 2066
First 2067
Second 2068
Third 2069
Fourth 2070
Fifth 2071
Sixth 2072
Seventh 2073
Eighth 2074
Ninth Edition 2075 (Revised and updated)
Tenth Edition 2076
Reprint

Copyright 
Publisher

Computer layout:
Oasis Desktop

Printed in Nepal

Preface

Oasis School Science for Grade 9 is an attempt to make learning process a joyful
experience. This textbook has been written in strict conformity with the latest syllabus
prescribed by the Curriculum Development Centre, Sano Thimi, Bhaktapur, Nepal. This
book has been designed to help students develop their conceptual thinking and scientific
skills. I think this book is an excellent introduction to experimentation and practical
application of Science. I hope it will greatly facilitate teaching learning process in an easy
and enjoyable manner.

The beauty of this textbook lies in having high resolution pictures, attractive layout, and
clear illustrations with lucid language. It emphasizes concept building rather than merely
focusing on providing and collecting information without critical thinking. I expect
this book will assist students to make them eager and quizzical learners that reinforces
their conceptual learning in the classroom. Besides the learning process of the students,
this book will help in teaching process of the teachers. Each unit of this book presents
subject matter in an interesting, understandable and enjoyable manner. The exercise at
the end of each unit includes a variety of questions to facilitate the integration of various
concepts taught. Above all, I sincerely believe that this book will be helpful in overall
understanding of Science in an interesting manner.

It is not a hidden fact that modern era is the era of science and technology. Science is a part
of the world we live in and an avenue to the technology. A good textbook in science should
assist the learners to realize different activities and events around us that encourages
them for further discovery and innovation interestingly. I strongly believe that students
should enjoy science and this book will be a means of enjoying and learning science in the
modern era of science and technology.

I wish to express my sincere gratitude to Mr. Harish Chandra Bista, Managing
Director of Oasis Publication Pvt. Ltd. for publishing this book. Similarly, my
hearty thanks go to Focus Computer for layout. Thanks are due to Mr. Deepak
Bhatta, Mr. Naresh Budal, Mr. Surendra Mishra, Mr. Navneesh Prasad Yadav,
Mr. Ram Maharjan, Mrs. Bimala Shah, Mrs. Jamuna Maharjan, Mr. R.C. Neupane,
Mr. Ujjwol Bhomi, Mr. Shivendra Karki, Mr. Binod Kumar Yadav, Mr. Prakash Bhatta, Mr.
Sudip Bajagain and Mr. Rabindra Agrawal for their valuable help during the preparation
of the book. Likewise, thanks are due to Mr. Ramesh Lamsal and Mr. Bhan Dev Kapadi for
their praiseworthy language editing. I gratefully acknowledge teachers across the country
as well as my well-wishers for their inspiration and support during the preparation and
publication of the book.

In my opinion, the real judges of a book are the teachers concerned and the students for
whom it is meant. Despite all my efforts, there might be textual as well as technical errors.
Therefore, constructive suggestions for rectification and improvement of the book would
be gratefully acknowledged and incorporated in further editions.

October 2018 Author
Kathmandu, Nepal

Contents

Physics

Unit 1 Measurement ...................................................................... 1
Unit 2 Force ..................................................................................... 17
Unit 3 Simple Machines................................................................. 40
Unit 4 Work, Energy and Power................................................... 57
Unit 5 Light...................................................................................... 72
Unit 6 Sound.................................................................................... 92
Unit 7 Current Electricity and Magnetism................................. 113

Chemistry

Unit 8 Classification of Elements.................................................. 136
Unit 9 Chemical Reaction.............................................................. 159
Unit 10 Solubility.............................................................................. 169
Unit 11 Some Gases.......................................................................... 183
Unit 12 Metals................................................................................... 203
Unit 13 Carbon and Its Compounds.............................................. 213
Unit 14 Water..................................................................................... 224
Unit 15 Chemical Fertilizers Used in Agriculture....................... 233

Biology

Unit 16 Classification of Plants and Animals.............................. 241
Unit 17 Adaptation of Organisms.................................................. 281
Unit 18 System................................................................................... 302
Unit 19 Sense Organs....................................................................... 328
Unit 20 Evolution.............................................................................. 341
Unit 21 Nature and Environment.................................................. 353

Geology and Astronomy

Unit 22 Natural Hazard.................................................................. 371
Unit 23 Greenhouse......................................................................... 382
Unit 24 The Earth in the Universe................................................. 390

Teaching Strategies

Science deals with the systematic knowledge of different activities and events that occur in our
surroundings. Therefore, various teaching learning activities can be adopted to Science according to
nature of the subject matter.
Teachers are expected to adopt various teaching methods like observation, experiment,
demonstration, discovery, invention, discussion, question-answer, field visit, etc. to teaching
learning process for Science. Besides these methods, teachers can adopt explanation or lecture
method in the course of introducing any event, subject matter or result of something. ‘Student
Centered Method’ is supposed to be the most appropriate in teaching Science. In this method,
every student gets chance to think critically in solving his/her problems.
In teaching learning activities, teachers are expected to make the involvement of every student in
‘process skills’ like classification, comparison, putting query, reasoning, keeping record, assessment,
etc. Teaching Science not only aims at accumulating knowledge but also at discovering knowledge.
Therefore, teaching learning process is expected to be centered on / oriented towards discovery
and invention.
Students should be encouraged to learn things on their own by discovering, inventing, experimenting
or by solving problems. For this purpose, teachers are expected to make the involvement of all the
students more and more in practical activities along with the theoretical knowledge.

Specially, for the successful teaching learning process, teachers are expected to keep the following
points in their mind.
i. Asking the students for the situations or events happening in their surroundings
ii. Encouraging the students to hypothesize in advance about the result or effect of the events

or situations
iii. Encouraging the students in testing their hypothesis

iv. Providing an opportunity to every student to reach his/her own conclusion and to rethink
of the significance of his/her conclusion

For effective teaching learning process teachers are expected to emphasize the use of teaching
learning materials. It is emphasized that the use of teaching learning materials is helpful to make
the concept of each lesson clear for easy understanding of the students. Teachers are expected to
make the optimum use of local teaching learning materials as far as possible according to nature
of the subject matter. For successful teaching learning process in Science, teachers are expected to
adopt to the following activities.

1. Figure/Picture Observation: The picture(s) or figure(s) related to the subject matter of the
lesson play(s) vital role in making the concept of the lesson clear. Teachers are expected to show
or demonstrate the picture(s) or figure(s) related to the lesson and to make the involvement
of the students in observation. This activity helps the students to take part in discussion and
question answer on the basis of their observation.

S.N. Area Estimated teaching periods Weighting
percentage
1. Physics Theory Practical Total
2. Chemistry 39 10 49 30.62
3. Biology 39 10 49 30.62
4. Geology and Astronomy 39 10 49 30.62
11 2 13 8.14
Total 128 32 160 100

2. Project Work: Project work is supposed to be an important activity in enhancing learning
capacity of the students. Teachers are expected to provide project work to the students
individually or in group(s) to be finished in limited time frame. After finishing the project
work(s), teachers are expected to provide an opportunity to the students to present the
process and result of the work in front of the class. This activity helps the students for their
further improvement.

3. Practice: It is well known saying that ‘learning without practice is meaningless.’ Therefore,
practice is one of the major components of a successful teaching learning process. In this
activity, teachers are expected to focus on the process of every finding rather than merely
focusing on finding answer(s). This activity provides an opportunity to the students for
their further improvement through the feedback from the teacher(s).

4. Activities: For the positive change in the concept, skill or attitude of the students,
performance of 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.

5. Field Visit: Teaching learning process for Science equally focuses on field visit according
to nature of the subject matter in the lesson. On the one hand, students naturally might
feel boring and monotony in classroom teaching only. On the other hand, nature of the
subject matter in Science demands for field visit for the familiarity of the students with
the environment and the different activities happening around us. Therefore, teachers
are expected to take the students outside the classroom to break their monotony as well
as make them familiar with surroundings. Teachers are expected to make the frequent
visit of the students to the concerning areas with their active participation. This activity is
supposed to be beneficial to the students that provides them the chance of self observation
and evaluation of the matter to enhance their knowledge in concerning fields.

Evaluation of the Students

Evaluation process for Science is taken as the interlinked part with the teaching learning process
of this subject. Teachers are expected to emphasize the continuous evaluation of the students
in terms of achieving intended goals rather than merely focusing on the formal written test.
Observation of the students’ activities is supposed to be the best method of evaluation in
Science.

Teachers are expected to make the involvement of the students in continuous teaching learning
process to achieve the intended goals. The evaluation process is expected to be continued
along with teaching process to identify students’ problems that helps both teachers as well as
students for their further improvement. Teachers can evaluate the students by various means
like evaluation of the class work, homework, project work as well as the evaluation of the
change in behaviour of the students. Specially, in Science, teachers are expected to evaluate
the students’ procedural skills and keep the systematic record of the achievements.

Compulsory Science

Part 1 : Physics
Scope and sequence of the subject matter

Area Unit Syllabus
Motion and Energy 1. Measurement
2. Force • Fundamental units and derived units
• Motion, force and inertia
• Newton’s equations of motion
• Balanced and unbalanced forces

3. Machine • Law of moment
• Mechanical advantage
• Velocity ratio
• Efficiency of machines

4. Work, Energy • Types of energy
and Power • Interrelationship between work, energy and power

Physical Phenomena 5. Light • Refraction
Around Us • Use of X-ray and ultra-violet ray

6. Sound • Sound wave
• Sources (Infra, audible and ultrasound)
• Intensity
• Utilities of reflection of sound

Current Electricity and 7. Current • Ohm’s law
Magnetism Electricity and • Resistance
Magnetism • Conductivity
• Magnetic field
• Magnetic lines of force
• Factors of terrestrial magnetism

Specification Grid-2074

S.N. Unit (K) (U) (A) (HA) Total Remarks

1. Measurement 5×1 4×2 2×3 1×4 23
2. Force
3. Machine
4. Work, Energy and Power
5. Light
6. Sound
7. Current Electricity and Magnetism



1UNIT Estimated teaching periods

Theory 3

Practical 1

MEASUREMENT

Objectives Kelvin

After completing the study of this unit, students will be able to:

• define fundamental units and derived units and describe the relation between
them.

• differentiate between fundamental physical quantities and derived physical
quantities.

• measure the length, mass, area, volume and time.

1.1 Introduction

In Physics, we study those quantities which can be measured. For example, the length of a book
can be measured, the mass of a piece of stone can be measured and the time taken by a person
to cover a distance of 500m can also be measured. The quantities which can be measured
are called physical quantities. Length, mass, time, volume, density, temperature, force, speed,
work, energy, power, electric current, etc. are some examples of physical quantities.

We use a large variety of gadgets such as bulb, radio, television, scooter, car, computer, etc.
whose operation is based on certain principles of Physics. Thus, to understand the fundamental
working principles of these things, study of Physics is quite essential.

To understand the relationship between the matter and energy, their measurement is very
necessary. Thus, we need to express and compare the magnitudes of different measurable
quantities, called physical quantities. For measurement of a physical quantity, we choose a
constant quantity of the same nature as a standard. Then we find a number which expresses
how many times the standard quantity is contained in the given physical quantity. So,
measurement is the comparison of an unknown physical quantity with a known standard
quantity of the same kind.

(a) Fig.1.1 (b)

measurement / ˈ m e ʒ ə m ə n t / - the comparison of an unknown physical quantity with a known standard quantity of the same kind

quantity / ˈ k w ɒ n t ɪ t i / - an amount or number of something

PHYSICS Oasis School Science - 9 1

1.2 Unit

A physical quantity is represented by a number, followed by a unit. The standard quantity
which is used for the comparison with an unknown quantity is called unit. In other words,
unit is a fixed quantity in terms of which other similar quantities are measured. So to find the
complete measurement, we must know the following:

i. the proper unit in which the quantity is measured.

ii. the numerical value which expresses how many times the above unit is contained
in the physical quantity to be measured. For example, if the mass of a cabbage is 2
kg, it means that unit of mass is kilogram (kg) and this unit is contained 2 times in
the mass of cabbage. Thus, we can say:

Physical quantity = Numerical value × Unit
(Mass) (2) (kg)

The unit selected for measuring a physical quantity should have the following properties.

i. It should not change with time, place and condition.
ii. It should be reproducible.
iii. It should be well defined without ambiguity.
iv. It should have a convenient size.

v. It should be easily available and accessible.

For these reasons, Nepal Government has a separate Department to monitor the
measuring devices in every two years to minimize discrepancy and remove the false
measuring devices from the market.

Activity 1

• Collect different rulers of the same type of scale. Mark any two points on a paper.
Measure the distance between these two points by using the different rulers. Why do
these scales give different measurement?

1.3 Classification of Physical Quantities

In Physics, we have to measure a very large number of physical quantities. So, it is difficult to
have separate units for each of them. Units of a few selected quantities are chosen and all other
quantities are expressed in terms of these quantities. So, length, mass and time are the three
fundamental physical quantities. Fundamental physical quantities are those quantities which
are independent of each other and other physical quantities can be compared with them. In
this regard, we can classify the physical quantities into two groups.

a. Fundamental physical quantities

b. Derived physical quantities

fundamental / f ʌ n d ə ˈ m e n t l / - forming the base from which everything else is made

2 Oasis School Science - 9 PHYSICS

a. Fundamental physical quantities

The physical quantities like length, mass, time, etc. are independent of each other and
not definable in terms of other physical quantities. Those physical quantities which
are independent of each other are called fundamental physical quantities, e.g. length,
mass, time, etc. In SI system, there are seven fundamental or basic physical quantities,
viz. length, mass, time, temperature, electric current, luminous intensity and amount
of substance. All other physical quantities can be obtained from these fundamental
quantities.

b. Derived physical quantities

Some physical quantities like area, force, velocity, density, etc. depend on one or more
fundamental physical quantities. Those physical quantities which are derived from
the fundamental physical quantities are called derived physical quantities, e.g. area,
volume, velocity, force, speed, work, power, pressure, etc. These physical quantities can
be expressed in terms of fundamental physical quantities.

Velocity is a derived physical quantity

Since, Velocity = Displacement = length [In terms of fundamental quantities]
Time taken time

Velocity is formed by the combination of two fundamental quantities, i.e. length and

time. So, it is called a derived physical quantity.

On the basis of above classification, units can also be classified into two groups. They are
fundamental units and derived units.

i) Fundamental units

Those units which are independent Reasonable fact-1

of each other are called fundamental The unit of length is called a basic or
units, e.g. metre (m), kilogram (kg) and fundamental unit. Why?
second (s). These units are not definable The SI unit of length is metre (m). This
in terms of other units. Fundamental unit is independent of other units and
units are the units of fundamental units of derived physical quantities can be
physical quantities. There are seven obtained by multiplying or dividing this
fundamental units in SI system. They unit. So the unit of length is called a basic
are: metre (m), kilogram (kg), second or fundamental unit.
(s), kelvin (K), ampere (A), candela (Cd)

and mole (mol.).

ii) Derived units Reasonable fact-1

Those units which are formed by the Why is the unit of power called a
combinationoftwoormorefundamental derived unit?
units are called derived units, e.g. m2,
m3, m/s, N, Pa, etc. These units can be The unit of power (i.e. watt) is called a
expressed in terms of fundamental derived unit because this unit is obtained
units. from three basic units: kilogram × metre2
× second-3 (kgm2s-3).

PHYSICS Oasis School Science - 9 3

1. The unit of velocity is a derived unit.

We know,

Velocity (v) = displacement (s)
time (t)

∴ Unit of velocity (v) = unit of distance or length (m)
unit of time (s)

Thus, the unit of velocity can be expressed in the fundamental units of length and time,
i.e. m/s or ms-1. Therefore, the unit of velocity is a derived unit.

2. The unit of power is a derived unit.

We know, Power (P) = work done (W)
time (t)

= force (F) × displacement (s) [∵ W = F×s]
time (t)

= mass(m)×acceleration(a)×displacement(s)

time (t)

Unit of power (P) = units of mass(m)×acceleration(a)×displacement(s)
unit of time (t)
kg × m/s2 × m
= s

T hus , th e unit of power, i.e. watt (W) can be expressed in the fundamental units of mass,

length and time, i.e. kg, m and s. Therefore, the unit of power is called a derived unit.

Following table shows some derived physical quantities with their units.

S. N. Physical Formulae SI units Symbols Fundamental
quantities units involved

1. Area length × breadth metre × metre m2 m×m
2. Volume
3. Density length × breadth × height metre × metre × metre m3 m×m×m

mass / volume kilogram / metre3 kg/ m3 kg/(m×m×m)

4. Velocity displacement / time metre/second m/s m/s

5. Acceleration change in velocity / time metre/second2 m/s2 m/(s×s)

6. Force mass × acceleration kilogram×metre/second2 kg m/s2 kg m/(s×s)

7. Work/Energy force × displacement newton-metre Nm or J kg×m×m/(s×s)

8. Power work / time joule /second or watt J/s or W kg×m×m/(s×s×s)

9. Pressure force/area newton/metre or pascal Nm-2orPa kg/(m×s×s)

10. Momentum mass × velocity kilogram×metre/second kg m/s kg×(m/s)
11. Frequency 1/time 1/second or Hz s-1 or Hz s-1

4 Oasis School Science - 9 PHYSICS

Differences between Fundamental units and Derived units

S.N. Fundamental units S.N. Derived units

1. Fundamental units are independent 1. Derived units depend on fundamental

of each other. units.

2. They are the units of fundamental 2. They are the units of derived physical

physical quantities. quantities.

3. There are seven fundamental units in 3. There are many derived units in SI

SI system. system.

Examples: m, kg, s, K, etc. Examples: m/s, N, W, J, etc.

1.4 Systems of Unit

The common systems of unit for measurement of physical quantities are given below:

1. MKS (Metric) system

The system of measurement in which length is measured in metre (m), mass is measured
in kilogram (kg) and time is measured is second (s) is called MKS system.

2. CGS (French) system

The system of measurement in which length is measured in centimetre (cm), mass is
measured in gram (g) and time is measured in second (s) is called CGS sytem.

3. FPS (British) system

The system of measurement in which length is measured in foot (ft), mass is
measured in pound (lb) and time is measured second (s) is called FPS system.
[1 pound (lb) = 0.454 kg]

4. SI system of unit

Three fundamental units, i.e. metre, kilogram and second are not sufficient for the study
of physics as a whole. So, MKS system was modified and enlarged by introducing more
physical quantities raising the number from three to seven. In October 1960, the 12th
General Conference of Weights and Measures adopted an international system of units
called SI units. The name SI is an abbreviation of the "System International d' Unites" in
French which means International System of Units.

The system of unit having seven fundamental physical quantities and their respective
units is called SI system of units. It can also be defined as the developed form of MKS
system by introducing more physical quantities as fundamental quantities. The following
table shows the fundamental quantities and their units in SI system.

conference /ˈkɒnfərəns/ - a large official meeting

PHYSICS Oasis School Science - 9 5

S. N. Fundamental quantities SI units Symbol
1. Length metre m
2. Mass kilogram kg
3. Time second s
4. Temperature kelvin K
5. Current ampere A
6. Luminous intensity candela Cd
7. Amount of substance mole mol.

SI unit also includes two supplementary units. These are as follows:

S. N. Fundamental Quantities Units (SI) Symbol

1. Angle Radian Rad
2. Solid angle Steradian sr

1.5 Measurement of Length

The distance between any two points is called length. It is measured in centimetre (cm), metre
(m), kilometre (km), etc. In SI system, length is measured in metre. One standard metre is
defined as the distance between two fine parallel golden lines engraved near the ends of a
platinum-iridium rod at standard atmospheric pressure which is kept at the International
Bureau of Weights and Measures near Paris, France. Eventually, modern science and
technology required a more precise standard than the distance between two fine scratches on
a metal bar. So, a new standard for metre was adopted in 1983 as follows:

One standard metre is the length of the path travelled by light in vacuum during a time interval
of 1/299792458 of a second. This number was chosen because the speed of light in vacuum is
exactly 299 792458 m/s.

Fig. 1.2

Multiple and Sub-multiple of metre Some smaller units of length

10 millimetre (mm) = 1 centimetre • Centimetre 1 cm = 10–2 m
• Millimetre 1 mm = 10–3 m
10 centimetre (cm) = 1 decimetre • Micron (µ) 1 micron (µ) = 10–6 m
• Nanometre (nm) 1 nm = 10–9 m
10 decimetre (dm) = 1 metre (m) • Angstrom (Å) 1Å= 10–10 m

10 metre (m) = 1 decametre (dam)

10 decametre (dam) = 1 hectometre (hm)

10 hectometre (hm) = 1 kilometre (km)

celestial / s ɪ ˈ l e s t ɪ ə l / - of the sky or of heaven
vacuum / ˈ v aek j ʊ ə m / - a space that is completely empty of all substances, including all air or other gas

6 Oasis School Science - 9 PHYSICS

Some bigger units of length

• Kilometre (km): It is equal to 1000m. It is used to measure the distance between two
cities or towns.

• Astronomical unit (AU): It is equal to mean (average) distance between the earth
and the sun.

1 AU = 1.496 ×1011m ≈ 1.5 × 1011 m

It is used to measure the distance between the celestial bodies within the solar system.
• Light year (ly): The distance travelled by light in one year in vacuum is called light

year.

1 ly = 9.46 × 1015 m

It is used to measure the distance of stars from the earth.
• Par sec: It is the abbreviated form for parallactic second. It is defined as the distance

at which an arc 1AU long subtends an angle of 1 second.

1 Par sec = 3.26 ly = 3.1 × 1016 m

Power of 10 Prefix Symbol Power of 10 Prefix Symbol
10–1 deci d 101 deca da
10–2 centi c 102 hecto h
10–3 milli m 103 kilo k
10–6 micro µ 106 mega M
10–9 nano 109 giga G
10–12 pico n 1012 tera T
10–15 femto p 1015 penta P
10–18 atto f 1018 exa E
a

1.6 Measurement of Mass

The total amount of matter contained in a body is called its mass.
It is measured in kilogram (kg), gram (g), milligram (mg), etc. The
mass of a body is measured by using a beam balance or a pan
balance. Kilogram is considered as a standard unit of mass.

Fig. 1.3 Beam balance

One standard kilogram

One standard kilogram is the mass of a platinum-iridium cylinder having equal diametre
and height kept at 00C at the International Bureau of Weights and Measures, Sevres near
Paris in France. The mass of this cylinder is equal to the mass of one litre pure water at 40C.

PHYSICS Oasis School Science - 9 7

Multiple and Sub-multiple of gram Smaller units and Special units of mass

10 milligram (mg) = 1 centigram 1 g = 10–3 kg

10 centigram (cg) = 1 decigram 1 mg = 10–3 g

10 decigram (dg) = 1 gram (g) 1 kg = 1000 g = 103g

10 gram (g) = 1 decagram (dag) 1 g = 0.001 kg = 10-3 kg

10 decagram (dag) = 1 hectogram (hg) 1 g = 1000 mg = 103 mg

10 hectogram (hg) = 1 kilogram (kg) 1 mg = 0.001g = 10-3 g

1 mg = 0.000001kg = 10-6 kg

Bigger units of mass To measure the mass of atomic particles
such as proton, neutron, etc. a unit called
1 quintal = 100 kg = 102kg atomic mass unit (amu) or the unified
atomic mass (u) is used.
1 metric tonne = 1000 kg = 103kg
1 amu (or u) is equal to
Quintal is used to measure the mass of
a bag of wheat, car, truck, etc. whereas 1 th of the mass of one C – 12 atom.
metric tonne is used to measure the mass 12
of a ship, a large telescope, etc.
∴1 amu (or u) = 1.66 × 10–27 kg.

1.7 Measurement of Time

The duration between any two events is called time. In scientific work, we want to know how
long an event lasts. It is called time interval. Clock is used to measure time. Second, minute,
hour, day, week, month, year, decade, century, millennium, etc. are the units in which time is
measured. The SI unit of time is second (s).

1 minute = 60 seconds Zenith
1 hour = 60×60 = 3600 seconds

1 day = 24×60×60 = 86400 seconds
1 year = 365×24×60×60 = 31536000 seconds = 3.1536×107s

Zenith

The point in the space just above the observer's head is called the
zenith.

One mean solar day: The time taken by the sun to return to the zenith from thFeige.a1r.t4h's surface
is called 1 mean solar day. It can also be defined as the time required by the earth to complete
its one rotation around the sun about its axis.

oscillation /ˌɒsɪˈleɪʃn/ - a regular movement between one position and another

8 Oasis School Science - 9 PHYSICS

One second is defined as 1 th part of a mean solar day. It can also
86400

be defined as the time interval of 9,192,631,770 periods of specified

energy change in the Caesium -133 atom.

Different time measuring devices

1. Mechanical watch Fig. 1.5 Mechanical watch

Mechanical watch works on the basis of the oscillation of a
simple pendulum. Due to the climatic condition, the length of the pendulum becomes
long and short. So, it cannot measure the time accurately. It is also called a pendulum
watch.

2. Quartz watch

Quartz watch works due to the vibration of quartz crystals. It is more accurate than the
mechanical watch.

1.6 Quartz watch 1.7 Atomic watch

3. Atomic watch
Atomic watch works due to the emission of radiation by Cs-133 isotopes. It

measures the time very accurately.

Activity 2

• Take a thread of about 50 cm length. Tie a metallic bob at the end of the thread. Note
down the time for 20 oscillations with the help of a stop watch. Calculate the time for
1 oscillation. This is the time period of the pendulum.

Differences between Pendulum watch and Quartz watch

S.N. Pendulum watch S.N. Quartz watch

1. It works on the basis of oscillations of 1. It works on the basis of vibrations of

the simple pendulum. the quartz crystal.

2. In a pendulum watch, the time given 2. In a quartz watch, the time given by
by it fluctuates by a few seconds to it may fluctuate by a few seconds in
minutes in a day. a month.

emission /ɪˈmɪʃn/ - the production or sending out of light

PHYSICS Oasis School Science - 9 9

1.8 Measurement of Area

The total surface occupied by a body is called its area. It is measured in square kilometre
(km2), square metre (m2), square centimetre (cm2), etc. The SI unit of area is m2.

Units of area
1 km2 = 1000000 m2 = 106 m2
1 cm2 = 0.0001 m2 = 10-4 m2
1 mm2 = 0.000001 m2 = 10-6 m2

The area of different objects with regular shape can be calculated by using the definite formula.
Some of them are as follows:

1. Area of a rectangle = length × breadth = l × b
2. Area of a square =
3. Surface area of a sphere = (length)2 = l2

4. Area of a triangle = 4π (radius)2 = 4π r2

1 base × height = 1 b × h
2 2

length length height

breadth r base
Triangle
Rectangle Square Sphere
Fig. 1.8

The area of an irregular body is calculated by graphical method.

Worked out Numerical 1

Calculate the area of a rectangle if the length and breadth are 10cm and 8cm respectively.

Express the result in SI unit.

Solution:
Given,

Length (l) = 10cm = 10 m = 0.1 m
100
8
Breadth (b) = 8cm = 100 m = 0.08 m

Area (A) = ?

We have,

A = l × b = 0.1 × 0.08 = 0.008 m2

∴ The area of the rectangle (A) = 0.008 m2.

10 Oasis School Science - 9 PHYSICS

1.9 Measurement of Volume V2
V1
The total space occupied by a body is called its
volume. It is measured in cubic metre (m3), cubic Solid object
centimetre (cm3), litre (l), millilitre (ml), etc.
The volume of a regular body can be calculated Before After
by a definite formula but the volume of an
irregular solid body is calculated by the liquid Fig. 1.9 Measuring cylinder
displacement method. The principle applied
for this method is:- when a body is completely
immersed in a liquid, the volume of the body is
equal to the volume of the liquid displaced by
that body. (It is to be noted that the solid to be
measured must be insoluble in liquid.)

Units of volume

1 mm3 = 0.000000001 m3 = 10-9 m3
0.000001 m3 = 10-6 m3
1 cm3 = 1000 millilitre (ml)
1 m3
1 litre = 0.001 litre (l)

1000 litre =

1 millilitre (ml) =

The volume (V) of some regular bodies is calculated by using the following formulae.
1. Volume of a cuboid = length × breadth × height = l × b × h

2. Volume of a cube = (length)3 = l3
3. Volume of a sphere =
4. Volume of a cylinder = 4 π (radius)3 = 4 πr3 = π (diameter)3 = πd3
3 3 6 6

π (radius)2 × height = πr2h

h r

l b l r l
Cuboid
ll Sphere Cylinder

Cube
Fig. 1.10

PHYSICS Oasis School Science - 9 11

Worked out Numerical 2

The diameter of a football is 12 cm. Calculate the volume of the football.

Solution:
Given,
Diameter (d) = 12 cm

∴ Radius (r) = d = 12 = 6 cm
2 2

We know,

V = 4 πr3 [∵ Football is a sphere.]
3

= 4 × 22 × 63 [∵ π = 272]
3 7

= 19008
21

= 905.142 cm3

∴ The volume of the football = 905.142 cm3.

Worked out Numerical 3

Calculate the volume of a cylinder of diameter 14 cm and height 8 cm respectively. Express
the result in SI unit.
Solution:
Given,

Diameter (d) = 14 cm

Radius (r) = d = 14 = 7 cm
2 2

Height (h) = 8 cm

Volume (V) = ?
We know,

V = πr2h

= 22 × 72 × 8 = 1232 cm3 = 1232 = 0.001232 m3
7 100×100×100

∴ The volume of the cylinder is 0.001232 m3.

1.10 Scientific Notation

When the distance between any two heavenly bodies is expressed in metre, it requires more
space and it consumes more time. Therefore, very large and very small numbers are expressed
in the power of ten which is known as scientific notation. It is also called standard notation.
It saves our time and space. While expressing a number in the scientific notation, following
points should be kept in mind.

12 Oasis School Science - 9 PHYSICS

(i) While shifting the decimal to the left, the power of ten should be increased by one
in each shift.

For example,

12345

= 1.2345×101×101×101×101 [The decimal point shifts to four steps left.]

= 1.2345×104
= 1.23 ×104

(ii) While shifting the decimal to the right, the power of ten should be increased by
minus one in each shift.

For example,

0.00034

= 3.4×10-1×10-1×10-1×10-1 [The decimal point shifts to four steps right.]

= 3.4×10-4

Worked out Numerical 4

Convert 2568.4187 into the scientific notation.
Solution:
Here, the decimal point shifts to three steps left.

∴ 2568.4187 = 2.5684187 × 103 ≈ 2.6 × 103

Worked out Numerical 5

Convert 0.00005845 into the scientific notation.
Solution:
Here, the decimal point shifts to five steps right.

∴ 0.00005845 = 000005.845 × 10–5 = 5.845 × 10–5 ≈ 5.8 × 10–5

Worked out Numerical 6

Convert the following scientific notations into the general form.

a. 2.5 × 10–4 b. 3.75 × 10–5 c. 3.567 × 10–7 d. 7.003 × 10–10 e. 1.23 × 105

Solution:

a. The decimal point moves to four steps left, 2.5 × 10–4 = 0.00025

b. The decimal point moves to five steps left, 3.75 × 10–5 = 0.0000375

c. The decimal point moves to seven steps left, 3.567 × 10–7 = 0.0000003567

d. The decimal point moves to ten steps left, 7.003× 10–10 = 0.0000000007003

e. The decimal point moves to five steps right, 1.23 × 105 = 123000

PHYSICS Oasis School Science - 9 13

SUMMARY

• The comparison of an unknown physical quantity with the known standard
physical quantity of the same kind is called measurement.

• The standard quantity which is used for comparison with an unknown
physical quantity is called unit.

• Those physical quantities which are independent of each other are called
fundamental physical quantities, e.g. length, mass, time, etc.

• Those physical quantities which are derived from the fundamental quantities
are called derived physical quantities, e.g. area, force, density, etc.

• One standard metre is defined as the distance between the two fine parallel
golden lines engraved near the ends of a platinum-iridium rod at standard
atmospheric pressure which is kept at the International Bureau of Weights
and Measures near Paris, France.

• One standard kilogram is the mass of a platinum-iridium cylinder having
equal diameter and height kept at 00C at the International Bureau of
Weights and Measures, Serves near Paris in France.

• The point in the space just above the observer's head is called the zenith.

• One second is defined as 1 part of a mean solar day.
86400 th

• The time taken by the sun to return to the zenith from the earth's surface is
called one mean solar day.

• The total amount of matter contained in a body is called mass. Its SI unit is
kilogram (kg).

• The total surface occupied by a body is called its area.

• The total space occupied by a body is called its volume. Its SI unit is cubic
metre (m3).

• The volume of a regular body can be calculated by a definite formula but the
volume of an irregular solid body is calculated by the liquid displacement
method.

• Very large and very small numbers are expressed in the power of ten which
is called scientific notation.

14 Oasis School Science - 9 PHYSICS

Exercise

Group-A

1. What is measurement?
2. What is MKS system?
3. What is fundamental unit?
4. Define derived unit.
5. What is SI system?
6. What is a physical quantity? Write with examples.
7. What is 'length'? Write down its SI unit.
8. Define one metre length.
9. What is the mass of a body? In which units is it measured?
10. Define one standard kilogram.
11. How is 'one second' time defined in SI system?
12. What is time? Write its SI unit.
13. Define one solar day.
14. What is longitude?
15. How does quartz watch give time? Write.
16. What is area? Write down the formula to calculate the surface area of a circular body.
17. What is 'volume of an object'? In which unit is it measured in SI system?
18. Write down the formula to calculate the volume of a cylindrical object.
19. How much time of a solar day is considered as one second?
20. Write down the SI units of the given physical quantities.
i) area ii) energy iii) acceleration iv) pressure v) moment vi) volume
vii) density viii) temperature ix) work
21. Why is the International Bureau of Weight and Measure established?
22. What is metric system?

Group-B

1. Mass is called a fundamental physical quantity but velocity is called a derived physical
quantity. Give reason.

2. The unit of length is called fundamental unit but the unit of density is called a derived
unit, why?

3. Write any two differences between fundamental units and derived units.

4. Write any two differences between fundamental physical quantities and derived physical

PHYSICS Oasis School Science - 9 15

quantities.
5. Standard weights and scales in the market should be checked in every two years, why?
6. Write any two differences between MKS system and CGS system.
7. Very large and very small numbers are written in the power of ten. Give reason.
8. Write any two differences between mechanical clock and quartz clock.
9. Why is newton called a derived unit?
10. Quartz clock is more appropriate than mechanical clock to measure time, why?

Group-C

1. Describe the importance of measurement in our daily life.

2. `Express newton and pascal in terms of fundamental units.

3. How is the volume of an irregular solid measured? Explain.

4. Express watt and joule in terms of fundamental units.

5. Express the following numbers in the scientific notation.

i) 2000085000 ii) 0.000825 iii) 2000.82

6. Convert the following scientific notations into the general form.

i) 3 × 108 ii) 1.5 × 10–5 iii) 2.57 × 10–7

7. Convert the following:

i) 54 km into cm ii) 2 mm2 into m2

8. The volume of water in a measuring cylinder is 50 ml. When a piece of stone is immersed

in the cylinder, the volume of water increases to 87.3 ml. Calculate the volume of the

stone. [Ans: 37.3 cm3]

Group-D

1. What is the advantage of scientific notation or standard notation? Explain.

2. The diameter of a football is 12 cm. Calculate its volume. [Ans: 905. 142 cm3]

3. Study the given figures and calculate the volume of each.

i) ii) O A

5 cm OA=8cm 12 cm

10 cm 2m

[Ans: i) 1×10-2 m3 ii) 2.413 × 103 cm3]

4. How is the volume of an irregular solid measured? Explain with neat figure.
5. Name the four systems of unit and explain any two of them.

16 Oasis School Science - 9 PHYSICS

2UNIT Estimated teaching periods

Theory 5

Practical 1

force

Objectives Sir Isaac Newton

After completing the study of this unit, students will be able to:

• describe and demonstrate inertia, motion and force of a moving body and the body at rest.
• explain Newton's laws of motion and state their application.
• differentiate between balanced force and unbalanced force
• calculate the acceleration of a body in motion.
• derive the equations of motion and solve the numerical problems related to these

equations.

2.1 Introduction

Force is one of the most important physical quantities. We are all familiar with the concept
of force from our common experiences. For example, opening and closing a door, kicking a
football, pushing a cart, lifting a bucket, beating a drum and so on. To perform these activities,
an effort is necessary which is called force. In everyday life, we use force to perform various
activities. Push, pull, squeeze, stretch, etc. involve a force.

Fig. 2.1(a) A man is pushing a car Fig. 2.1 (b) A man is pulling a cart

Consider a ball is kept on a table. We can move it by pushing or pulling. Now consider the
same ball rolling on the table. We can increase its speed by pushing it in the direction of its
motion. If we push it in the opposite direction of its motion, the speed of the ball decreases.
What happens when a ball moving towards east is pushed towards north? It changes the
direction of the ball. In all these cases, we have applied a force on the ball and the ball is
accelerated. So to accelerate an object, one must apply a force on it. Therefore, "force is the
push or pull which changes or tries to change the position, i.e. the state of rest or uniform
motion, of a body."

squeeze /skwiːz/ - to press sth firmly with fingers

PHYSICS Oasis School Science - 9 17

2.2 Rest and Motion

When you are sitting in a moving bus, the position

of your body with respect to other seats or passen-

gers remains constant. As compared to another

passenger your position is not changing. So, you

are at rest with respect to other seats or passen-

gers. But the distance between you and any tree

near the road is changing as time passes. So, you

are moving with respect to the tree. Thus, the same

object at the same instant can be at rest with re-

spect to one thing and in motion with respect to Fig. 2.2
some other things. Motion is not absolute, neither

is rest. The state of any object depends on the other objects with respect to which the position

of a body is compared.

Let us consider a bus at rest near a tree. When the bus starts to move, it changes its position
with respect to the tree. Similarly, the driver also changes its position with respect to the tree.
But the driver is not changing his position with respect to the bus.

Activity 1

• Observe the position of any ten objects like house, tree, bird, water, etc. Find out
which are in a state of rest and which are in motion. What can you conclude from
this activity?

2.3 Units of Force

The SI unit of force is newton. The symbol of newton is N [1N = 1kg ×1m/s2].

The CGS unit of force is dyne [1 dyne = 1 g ×1 cm/s2].
Relationship between newton and dyne

1 newton = 1 kg × 1m/s2 [∵ F = m×a]
= 1000g ×100cm/s2
= 100000g cm/s2
= 105 g cm/s2

= 105 dynes

∴ 1 newton = 105 dynes

Apart from moving an object, the shape of the object can also be changed by applying force on
it. If you take a soft rubber ball between your palms and push it from both sides, the shape of
the ball will be changed.

18 Oasis School Science - 9 PHYSICS

2.4 Effects of Force

A force can produce the following effects on a body.
i. Force can change the state (rest or motion) of a body.
ii. It can change the direction of motion of a body.
iii. It can change the shape of a body.
iv. It can change the speed of a moving body.

2.5 Vectors and Scalars

Some physical quantities such as time, speed, distance, etc. can be described by their magnitude
only whereas other physical quantities like velocity, force, displacement, etc. need magnitude
as well as direction to describe them.

Those physical quantities which have both magnitude as well as direction are called vectors or
vector quantities, e.g. displacement, velocity, acceleration, force, etc.

Those physical quantities which have only magnitude are called scalars or scalar quantities,
e.g. distance, speed, mass, time, pressure, work, energy, area, volume, etc.

Vectors are added by the rules of vector algebra but scalars are added by simple algebra.
Vectors are written in a special way but sc→alars have no special way of writing the letters. For
example: Vector AB is denoted by AB or AB . If two or more vectors are added, the sum may
be zero or positive or negative. But the sum of scalars is always positive.

Sum of two vectors
a. In the opposite direction

F1 = 3N F2 = 3N

In the given diagram, 3N force is being applied from each of the two opposite faces of the
body simultaneously.

Let F1 = 3N towards east then F2 = 3N towards west.
We see that F1 is opposite to F2. Assume F1 is in +ve direction, then F2 is opposite of F1.
∴ F2 is negative.
Thus, the sum of two vectors F1 and F2 = F1 + (–F2) = F1 – F2 = 3N – 3N = 0
b. In the same direction

F1 = 3N }F1 = 3N towards west
F2 = 3N
F2 = 3N

acceleration /əkseləˈreɪʃn/ - the rate of change in velocity of a moving body Oasis School Science - 9 19
PHYSICS

Let,

Take F1 has a positive direction. Then, F2 also has a positive direction because it has the
same direction as F1.

The sum of the two vectors F1 and F2 = F1 + F2

= 3N + 3N

= 6N
Differences between Vectors and Scalars

S.N. Vectors S.N. Scalars

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

2. The sum of vectors may be positive 2. The sum of scalars is always positive.
or zero or negative.

3. Vectors are added by the rules of 3. Scalars are added by the rules of simple

vector algebra. algebra.

Examples: Force, displacement, Examples: Distance, mass, speed, etc.
velocity, etc.

2.6 Distance and Displacement

Suppose a person is at place A. He has to reach B and then C. Now, the person starts from A
and travels a distance of 4 km to reach B, and then travels another 3 km from B to C. Thus, the
person goes along the path ABC. The total length AB + BC is the actual length to be covered.
Thus, the actual length travelled by a body is called distance. In this example, actual path or
distance traveled is

AB + BC = 4 km + 3 km = 7 km.

C

D5iskpmlacement 3 km

A 4 km B

Fig. 2.2

As the person reached point C, we can find out how far he is from the initial point A or the
shortest distance between A and C. The shortest distance (or distance of AC) is 5 km. The
distance travelled by a body in a certain direction is called displacement. Distance is a scalar
quantity and is always taken as a positive quantity, whereas displacement is a vector quantity
and it may have positive, zero or negative value. Displacement does not depend on the path

20 Oasis School Science - 9 PHYSICS

followed by a moving body but it depends only on the initial and final positions of a moving
body. The SI unit of both distance and displacement is metre (m).

Differences between Distance and Displacement

S.N. Distance S.N. Displacement
1. 1.
Distance is the total length covered Displacement is the shortest distance
2. by a moving body in a certain inter- 2. between initial and final positions of a
3. val of time. 3. moving body.

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

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

2.7 Speed and Velocity

If a car travels a distance of 500 km in 10 hours, the speed of the car is 500/10 = 50 km/h, that is
the car travels 50 km in every hour. Thus, the speed of a body gives the idea of how fast a body
is moving but it does not indicate the direction of motion of the body. So, speed is defined as
the rate of change of distance.

Speed = Distance (s)
Time taken (t)

The SI unit of speed is m/s and its CGS unit is cm/s.

But speed in a particular direction is called velocity. So, velocity is defined as the rate of change
of displacement. Speed is a scalar but velocity is a vector quantity.

Velocity (v) = Displacement (s)
Time taken (t)

The SI unit of velocity is m/s and its CGS unit is cm/s.

Differences between Speed and Velocity

S.N. Speed S.N. Velocity

1. Speed is the rate of change of distance. 1. Velocity is the rate of change of
displacement.

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

3. It cannot be zero. 3. It can be zero.

Worked out Numerical 1

A car travels a distance of 15 km in 10 minutes towards the east. Calculate the velocity of
the car.

Solution:

Displacement (s) = 15 km

= 15 × 1000 m [∵ 1 km = 1000 m]
= 15000m

PHYSICS Oasis School Science - 9 21

Time taken (t) = 10 min.

= 10×60 = 600 s [∵ 1 min. = 60 seconds]

Velocity (v) = ?

We know, s 15000
t 600
v= = = 25 m/s

∴ The velocity of the car = 25 m/s.

2.8 Acceleration

When a body is moving with an increasing velocity, the body is said to be accelerated. Suppose

a body is moving from the rest and the velocity of the body reaches 10m/s in 5 seconds. The

change in velocity of the body is 10 m/s – 0 m/s. Thus, in every second velocity changes by

10 m/s = 2 m/s. The body is said to have changing velocity of 2 m/s in every second. It means
5
that the body is accelerating at the rate of 2m/s2.

The rate of change in velocity of a moving body is called acceleration. Its SI unit is metre
per second per second (m/s2). The acceleration of a moving body is calculated by the given
formula.

Acceleration (a) = change in velocity
time taken

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

∴a = v–u
t


The negative acceleration or the rate of decrease in velocity of a moving body is called

retardation. It has the same unit as that of the acceleration. A moving body is said to be in the

state of retardation when its velocity decreases.

Worked out Numerical 2

Calculate the acceleration of a truck if it starts from the rest and attains a velocity of 14m/s
in 2s.

Solution:

Initial velocity (u) = 0 (∵ The truck starts to move from rest.)

Final velocity (v) = 14 m/s

Time (t) = 2s

Acceleration (a) = ?

We have,

a = v–u = 14–0 = 7 m/s2.
t 2

∴ The acceleration of the truck is 7m/s2.

retardation /riːtɑːˈdeɪʃn/ - the rate of decrease in velocity of a moving body

22 Oasis School Science - 9 PHYSICS

2.9 Graphical Representation of Motion

A moving body changes its position continuously with time. Graphical method is the simplest
way to describe the motion of a moving body. A graph is very useful in studying the linear
motion of a body. Here, we will discuss the motion of a body with the help of (1) distance -
time graph and (2) velocity - time graph.

1. Distance – time graph

Distance-time graph is the geometrical relationship between the distance covered by a
body and the time taken. It helps us to calculate the speed of a body at any instant of time.
In this graph, time is plotted along the X – axis and distance travelled by the body is plotted
along the Y – axis. The speed of a moving body can be calculated from the distance-time
graph. For a body in motion, different types of distance-time graphs are as follows:

Y Y

Y

20 20 20

15 15 15
Distance (m)
Distance (m)
Distance (m)
10 10 10

55 5

01 2 3 4 5 X 01 2 3 4 5 X 01 2 3 4 5 X
Time (s) Time (s) Time (s)

a) Body at rest b) Uniform speed c) Non-uniform speed

Fig. 2.3

a. Body at rest
When a body is at rest, we get a straight line parallel to the time axis.

b. Uniform speed

When a body moves with a uniform speed, it travels equal distance in equal interval
of time. The distance – time graph for the uniform speed is always a straight line
making an angle with the X-axis. The straight line may or may not pass through
the origin.

c. Non-uniform speed

When a body moves unequal distance in equal interval of time, it is called non-
uniform speed. A curve represents the non-uniform speed.

2. Velocity-time graph

Velocity-time graph is the geometrical relationship between the velocity of a body and
the time. The velocity-time graph for a moving body can be drawn by plotting the
velocity of the body along the Y-axis and the time along the X-axis. For a straight line
motion, different types of velocity-time graphs are given below:

PHYSICS Oasis School Science - 9 23

Y Y Y

25 25 25

20 20 20
Velocity (m/s)
Velocity (m/s)1515 15
Velocity (m/s)
10 10 10

5 234 5 X 5 234 5 X 5 234 5 X
01 Time (s) 01 Time (s) 01 Time (s)

a) Constant velocity b) Uniform acceleration c) Non-uniform acceleration

Fig. 2.4

a. Constant velocity

If the velocity of a moving body remains constant, a straight line parallel to time
axis is obtained. The acceleration of a body moving with constant (uniform)
velocity is zero.

b. Uniform acceleration
If the velocity changes equally in equal interval of time, the acceleration is called

uniform acceleration. The velocity-time graph for this motion is a straight line
making an angle with the time axis.

c. Non-uniform acceleration
If the velocity changes unequally in equal interval of time, the acceleration is

called non-uniform acceleration. The velocity-time graph for this motion is a curve
moving upwards.

Note: A

The slope of distance-time graph gives the speed of a moving
body and displacement-time graph gives the velocity. Similarly,
slope of velocity-time graph gives the acceleration of the
moving body.

How to calculate the slope of a line?

Calculate the value of tanθ, i.e. θ B
O Fig. 2.5
perpendicular (p)
tanθ = base (b) = AB = slope of OA.
OB

Worked out Numerical 3 Velocity (m/s) 6 AB
4
Study the given velocity-time graph of a body 2 D E C
and answer the following questions: 2 5 8
O
a. Name the motion represented by OA, AB Time (s)
and BC.
Fig. 2.6

24 Oasis School Science - 9 PHYSICS

b. Calculate the acceleration.
c. Calculate the retardation.

Solution:

a. OA is the straight line graph of velocity – time. So it represents uniform acceleration. AB
is the straight line graph parallel to time axis (X - axis). So, AB represents the uniform
velocity (or constant velocity). It has zero acceleration.

BC is a straight line graph between velocity and time which is sloping downward from
B to C. Thus, it represents the uniform retardation (or negative acceleration).

b. OA represents acceleration. To find acceleration, it is necessary to calculate the slope of

the graph OA. Therefore,

Acceleration (slope of OA) = AD = 6m/s = 3 m/s2.
DO 2s

c. BC represents retardation. To find retardation, it is necessary to calculate the slope of the

graph BC. Therefore,

Retardation (slope of BC) = BE = 6 = 6 = 2 m/s2.
EC 8–5 3

2.10 Equations of Motion

There are three equations which describe the motion of a body moving with a uniform
acceleration. Those equations give the relation among the initial velocity, final velocity, time
taken, acceleration, and the distance travelled by moving bodies. The various equations of
motion are derived below:

i. v = u + at

This equation helps us to find the velocity gained by a moving body in time t.

Let us consider a body has initial velocity 'u'. Suppose, it is subjected to a uniform
acceleration 'a' so that the final velocity becomes 'v' after time ’t’. Now, from the
definition of acceleration, we have

Acceleration = Change in velocity
Time taken

or, Acceleration (a) = Final velocity (v) – Initial velocity (u)
Time taken (t)
v–u
or, a = t

or, at = v – u

or, v = u + at . .................... (1)

ii. v2 = u2 + 2as

Let us consider a body is moving with an initial velocity 'u'. Let its velocity be 'v'
after time 't' and the distance travelled be 's'. The average velocity is the mean of
initial and final velocities. Therefore,

equation /ɪˈkweɪʒn/ - a statement showing that two amounts or values are equal

PHYSICS Oasis School Science - 9 25

Average velocity = Initial velocity + Final velocity
2

i.e. vav = v+u
2

Also,

Distance travelled (s) = Average velocity × Time taken

or, s = vav × t
or, s =
or, s = v+u × t
or, s = 2
or, 2as =
v+u × v–u [ ∵t= v–u ]
2 a a

v2–u2
2a

v2 – u2

∴ v2 = u2 + 2as .................... (2)

iii. s = ut + 1 at2
2

Let us consider a body is moving with an initial velocity 'u'. Let its velocity be 'v'

after time 't' and the distance travelled be 's'. Then,

Average velocity = Initial velocity + Final velocity
= 2
i.e. vav
Also, = u+v
2
Distance travelled (s)
Average velocity × Time taken

or, s = u+v × t
2

or, s = u + (u+at) × t [ ∵ v = u + at ]
2

or, s = ut+ut+at2
2

or, s = 2ut + at2
2

or, s = 2ut + at2
∴ 2 2

s = ut + 1 at2 ……………………….(3)
2

Some points to be remembered while solving the numerical problems related to motion.

i. If a body starts from rest, its initial velocity is zero, i.e. u = 0.

ii. If a body comes to rest, its final velocity is zero, i.e. v = 0.
iii. If a body moves with a uniform velocity, its acceleration is zero, i.e. a = 0.

26 Oasis School Science - 9 PHYSICS

Worked out Numerical 4

A car starts to move from rest and attains an acceleration of 4 m/s2 after 10 seconds. Calculate
the distance covered by the car.

Solution:

Initial velocity (u) = 0 (∴ The car starts to move from rest)

Acceleration (a) = 4 m/s2

Time taken (t) = 10 s

Distance covered (s) = ?

We have,

s = ut + 1 at2
2
=
= 0 × 10 + 1 × 4 × (10)2
2

200 m

∴ Distance covered by the car (s) = 200 m.

Worked out Numerical 5

Calculate the acceleration of a body moving with a constant velocity of 5 m/s.
Solution:
If a body is moving with a constant velocity, the acceleration is zero.

Initial velocity (u) = 5 m/s

Final velocity (v) = 5 m/s

Acceleration (a) = ?

We have, a = v–u = 5 – 5 = 0 =0
t t t

∴ The acceleration of the moving body with a constant velocity (a) = 0.

2.12 Mass and Inertia

A table lying in a room remains at rest unless an external force is applied on it. Similarly, a
force is required to change the speed or direction of a moving body. The inability of a body to
change its state (rest or motion) by itself is called inertia. The greater the inertia of a body, the
greater will be the force required to change the state of rest or uniform motion of that body.
Inertia is that property of a body due to which it resists change in its state.

PHYSICS Oasis School Science - 9 27

Activity 2 Empty can Sand filled can

• Take two cans of equal size. Fill one of the cans with Fig. 2.7
sand. Suspend both cans and apply force to move
them. Note which one oscillates for a longer time?
Why?

Inertia of a body is directly proportional to its mass.
So, the body with greater mass, i.e. the can filled
with sand, oscillates for a longer time.

The amount of the force required to change the state (rest or motion) of a body depends on its
mass, shape and the nature of its surface. A body having more mass has more inertia and less
mass has less inertia. So, a large amount of force is required to move a body with large mass
and vice versa. In fact, mass is the measure of the inertia of a body.

Types of Inertia

1. Inertia of rest

Inertia of rest is the inability of a body at rest to change its state of rest by itself. According
to the law of inertia of rest, a body continues to be in a state of rest unless an external
force acts on it.

Activity 3

• Take a stone of 1 kg mass and suspend it with Fig. 2.8
the help of a thread. Hang a small piece of thread
below the stone as shown in the diagram. Pull the
free end of the thread with a sudden jerk when
the stone is at rest. What happens?

The thread below the stone breaks due to the
inertia of rest of the stone. The upper part of the
thread does not break though both parts of the
thread are of the same quality.

Some examples of inertia of rest

i) When a branch of a tree with fruits is shaken, the fruits fall down. This happens because
the branch comes into motion, but the fruits remain in a state of rest due to inertia of rest.
As a result, fruits get detached from the tree and fall down.

ii) When a bus starts to move suddenly, a passenger standing inside it feels a backward jerk.
This is because the feet of the passenger, which are in contact with the floor of the bus,
start moving. But the upper part of the body tends to remain at rest due to the inertia of
rest. Hence, the passenger leans backwards.

iii) When a carpet is beaten with a stick, dust particles are cleared. This is because the carpet

inertia /ɪˈn‰ːʃə/ - the inability of a body to change its state of rest or motion

28 Oasis School Science - 9 PHYSICS

comes into motion when it is beaten but the dust particles remain at rest due to the
inertia of rest and fall down under the effect of gravity.

iv) When a cardboard carrying a coin over a glass is flipped away quickly with a finger, the
coin falls into the glass. This is because, initially the card and the coin are both at rest. On
flipping, the cardboard is suddenly set into motion but the coin remains at rest due to the
inertia of rest. Hence, the coin drops into the glass.

Cardboard

Coin Glass

Fig. 2.9 Interia of rest

v) A bullet fired against a window pane makes a clear hole in the glass without cracking it.
This happens because the piece of glass in contact with the bullet comes into motion, but
the remaining part of the glass remains in a state of rest due to inertia. As a result, the
bullet makes a clear hole in the glass without cracking it.

vi) When a horse starts running suddenly, the rider is thrown backward. This happens because
the lower part of the rider's body comes into motion along with the horse, but the upper part
of the rider remains in a state of rest due to inertia. As a result, the rider falls backwards.

2. Inertia of motion

Inertia of motion is the inability of a moving body in a straight path to change its state
of motion by itself. According to the law of inertia of motion a body continues to be in a
state of uniform motion in a straight line unless an external force acts on it.

Some examples of inertia of motion
i) When a moving bus suddenly stops, the passengers fall forward. As the bus suddenly

stops, the lower part of body of the passengers being in contact with bus comes to rest
while the upper part remains in a state of motion due to inertia of motion. Hence, the
passengers fall forward.

ii) An athelete runs some distance before taking a long jump. By doing so, the velocity
acquired by the athelete is added to the velocity taken by him at the time of jump. Hence,
the athlete is able to jump over a longer distance.

iii) When a passenger sitting in a train moving in a 'uniform' velocity throws a ball vertically
upwards, the ball returns to his hand. This is because during its upward and downward
motion, the ball continues to move horizontally with the velocity of the train. It happens
so because of the inertia of motion.

iv) A person getting down from a speeding bus falls in the direction of motion of the bus.
This is because the feet of the person come to rest on touching the ground but the body

PHYSICS Oasis School Science - 9 29

continues to move due to the inertia of motion. Hence, when a person gets down from a
running bus, he must run on the ground for some distance in the direction of the motion
of the bus. By doing so, the whole body remains in motion and the person can stop his
whole body by applying a force by his muscles. Similarly, he must run for some distance
before entering a speeding bus.
v) An electric fan continues to move for sometime even after the electricity is switched off
due to inertia of motion.
vi) The rider falls forward when the running horse stops suddenly due to inertia of motion.
vii) A running soldier cannot stop instantly when the commander orders to stop due to
inertia of motion.

Reasonable fact-1

The blades of a fan do not come to rest immediately after the circuit is switched
off. Why?
The blades of a fan move due to continuous supply of electricity. But when the switch is
turned off to cut the supply of electricity, the blades of the fan remain moving for a while
due to inertia of motion.

Reasonable fact-2

A bullet fired against a glass windowpane makes a hole in it without cracking the
windowpane. Give reason.
The entire glass of windowpane is in the state of rest initially. The part of glasspane which
comes in contact with a fired bullet shares the large velocity of the bullet and flies away
making a hole. But the remaining part of the windowpane remains at rest due to inertia of
rest and is not cracked.

2.12 Momentum

A force is required to stop a moving body. The force required to stop a moving body is directly
proportional to its mass and velocity. Thus, the magnitude of motion in a body depends on
the mass (m) and velocity (v) of the moving body, which is called momentum (p). So the
momentum of a body can be defined as the product of its mass and velocity.

Thus, Momentum (p) = Mass (m) × Velocity (v)

From the above relation, it is clear that if a body is at rest, its velocity is zero and hence its
momentum is zero. Thus, the total momentum of the gun and bullet before firing is zero as
their velocity is zero.

The SI unit of mass is kilogram (kg) and that of velocity is metre per second (m/s). So the SI
unit of momentum is kilogram metre per second (kg. m/s). Momentum is a a vector quantity
and takes place in the direction of velocity.

30 Oasis School Science - 9 PHYSICS

Worked out Numerical 6

Calculate the momentum of a car of mass 500 kg when it is moving with a uniform velocity
of 25 m/s.
Solution:
Given,

Mass (m) = 500 kg
Velocity (v) = 25 m/s
Momentum (P) = ?

We have,
Momentum (P) = Mass (m) × Velocity (V) = 500 × 25
= 12500 kg m/s
∴ The momentum of the car = 12500 kg m/s.

Momentum of a body depends on the mass and velocity of the body. Though a cricket ball
is not very heavy, when it is thrown with a high speed it hurts the batsman as it acquires a
very large momentum. This is why a batsman often ducks to a bouncer. On the other hand, a
car or bus may not be running at a high speed but because of its high mass, it has a very high
momentum which may hurt the person coming on its way.

2.13 Newton's Laws of Motion

Sir Isaac Newton, the famous British scientist, has given three laws to describe the motion of
bodies. These laws of motion were published in the book, 'The Principia Mathematica'. These
laws are very useful to describe the motion of different bodies.

1. Newton's First Law of Motion
Newton's first law of motion states that, "Every body continues to be in a state of rest or of
uniform motion in a straight line unless an external force is applied on it". This law is also
called law of inertia. This law defines the force. For example, a book on the table remains there
until we remove it or displace it. Similarly, a moving body continues to move in a straight line
with a uniform velocity unless some external force acts on it. This means a body cannot change
its state of rest or state of uniform motion. This inability of a body to change by itself its state
of rest or of uniform motion is called inertia of the body. So, Newton's first law of motion is
also called the law of inertia.

According to Newton's first law of motion, a body changes its state of rest or state of uniform
motion only when an external force is applied on it. Therefore, we define force as an external
agency which changes or tries to change the state of an object, direction of motion, etc. Hence,
Newton's first law defines the force.

injury /ˈɪn(d)ʒəri/ - harm done to a person's or animal's body

PHYSICS Oasis School Science - 9 31

Activity 4

• Take a piece of wood and push it over the table. Notice how long it moves. Why
does it come to rest?

Due to the friction between two surfaces, the wooden piece comes to a rest.

2. Newton's Second Law of Motion

Newton's second law of motion gives a relationship between force and acceleration. Newton's
second law of motion states that, "Acceleration produced on a body is directly proportional to
the force applied on it and inversely proportional to its mass.” This law gives us a method of
measuring the force in terms of mass and acceleration.

Let us consider a body of mass 'm' is moved by a force 'F'. If 'a' is the acceleration produced on
the body, according to Newton's second law of motion,

The acceleration (a) produced on a body is directly proportional to the force (F) applied on it,

i.e. a ∝ F………… (i)
The acceleration (a) produced on the body is inversely proportional to the mass (m) of the body,

i.e. a ∝ 1 ………. (ii)
m

Combining (i) and (ii), we get

a ∝ F
m

or, F ∝ ma

or, F = kma ……….. (iii) (where 'k' is a constant of proportionality)

Let, F = 1N, m = 1 kg and a = 1m/s2 then,

k = 1

Putting the value of k in equation (iii), we get
F = 1. ma

∴ F = ma

Applications of Newton's Second Law of Fig. 2.10 Cricketer catching a ball by
Motion lowering his hand

A cricket player lowers his hands while catching a
ball to stop it. If a cricket player stops a fast moving
cricket ball suddenly, the change in the velocity of
the ball from high value to zero value will be in a
very short time. So the ball exerts a great force on
the hand which may hurt the hand when the player
stops the ball suddenly.

32 Oasis School Science - 9 PHYSICS

On other hand, when the cricket player stops the same ball gradually by lowering his hands
towards the direction of the moving ball, he takes a longer time to stop the ball. The same
change in the velocity of the ball occurs in a longer time. So the ball exerts less force and no
injury will be caused to the hands of the player. Therefore, a cricket player lowers his hands
while catching a ball to prevent his hands from injury.

Similarly, when a man falls from a height to a concrete floor, he receives greater injuries than
one who falls on a sandy floor from the same height.

One newton force

The force which produces 1 m/s2 acceleration on a mass of 1 kg is called 1 newton force.

We have, F = ma

1N = 1 kg × 1m/s2

Relation between newton and dyne

We have, F = ma

1N = 1kg × 1m/s2

= 1000 g × 100 cm/s2 [∵1 kg = 1000 g and 1m = 100 cm]

= 100000 gcm/s2

= 100000 dyne

∴ 1N = 1 × 105 dyne

Worked out Numerical 7

A vehicle of mass 1000 kg is moving with a speed of 25 m/s. Calculate the acceleration of
the vehicle if it is stopped in 5 seconds by applying brakes on it. Also, find out the force
applied by the brakes.

Solution: = 1000 kg

Given, Mass of the vehicle (m) = 25 m/s

Initial velocity (u) =0
= 5s
Final velocity (v) =?
Time taken (t)
Acceleration (a)

Force (F) =?

We have, a = v–u
t

= 0–25 = – 5 m/s2
5

A ga in, F = ma

= 1000 × (–5)

= – 5000 N

PHYSICS Oasis School Science - 9 33

The negative sign shows that the force applied by the brakes is opposing the motion of
the vehicle.

3. Newton's Third Law of Motion Fig. 2.11 Boatmen rowing a boat

Whenever one body exerts a force on another body, the
second body exerts an equal and opposite force on the
first body. The force exerted by the first body is called
"action" whereas the force exerted by the second body
on the first body is called "reaction". Both action and
reaction are just forces. According to Newton's third law
of motion, "To every action there is an equal but opposite
reaction".

It means that when a body X exerts a force on a body Y,
the body Y will also exert an equal but opposite force
on the body X. Action and reaction act on two different
bodies, but they act simultaneously. Therefore, these
two equal but opposite forces do not cancel each other.

Fig. 2.12 A boat moves backward
when a man jumps out of it

Reasonable fact-3

A gun recoils when a shot is fired from it. Give reason.
When a bullet is fired from a gun, the bullet goes out due to the force applied on it (this is
action). According to Newton's third law of motion, the gun gives a backward jerk to the
shoulder of the gunman due to the reaction acting on it in opposite direction. Hence, the
gun recoils when a short is fired from it.

Reasonable fact-4

A rocket releases a lot of hot gases before taking off, why?
When hot gases come out of the nozzle of a rocket with a great force (i.e. action), the equal
but opposite force pushes the rocket forward according to Newton's third law of motion. As
a result, the rocket moves forward with a great speed.

Activity 5

• Take a balloon. Fill it with air. Close its mouth with two fingers and release it.
Observe the motion of the balloon. Why does the balloon move upward?

The air in the balloon comes out with a certain force called action. This exerts
a force on the balloon called the reaction force. As a result, the balloon moves
upward.

row /rəʊ/ - to move a boat through water using oars

34 Oasis School Science - 9 PHYSICS

2.14 Balanced and Unbalanced Force

A force is a pull or a push. A force can give energy

to an object causing the object to start moving, stop
moving or change its motion.

Forces occur in pairs and can be either balanced or
unbalanced. Balanced forces do not cause a change
in motion. They are equal in size and opposite in
direction.

Have you ever had an arm wrestling competition

with someone? If you compete against someone who

is just about as strong as you are, there will probably Fig. 2.17

be a time when both of you are pushing as hard as

you can, but your arms stay in the same place. This is

an example of balanced forces. The force exerted by each person is equal, but they are pushing

in opposite directions, in this case together. The two forces cancel each other out and the

resulting force is zero. Therefore, there is no change in motion.

Another example of balanced forces in action is in tug of war. In this case the forces are moving
away from each other and if two teams have equal strength or force, the rope will stay in the
same place. As a result there is no change in motion since the resultant force is zero.

Fig. 2.13

The forces are said to be balanced forces, when a number of forces acting on a body do not
change the state of rest or uniform motion in a straight line.

Unlike balanced forces, unbalanced forces always cause a change in motion. They are not equal
and opposite. When two unbalanced forces are exerted in opposite directions their combined
force is equal to the difference between the two forces and is exerted in the direction of the
larger force. Pushing a book on a table, kicking a football, pulling a small cart, etc. are some
examples of unbalanced forces. Unbalanced forces can also be exerted in the same direction.
The forces are said to be unbalanced, when a number of them acting on a body change its state
of rest or motion in a straight line.

PHYSICS Oasis School Science - 9 35

Fig. 2.14

SUMMARY

• Force can be defined as push or pull which changes or tries to change the
position of a body. In SI system force is measured in newton (N).

• Those physical quantities which have both magnitude as well as direction are
called vectors, e.g. acceleration, displacement, etc.

• Those physical quantities which have magnitude only are called scalars,
e.g. speed, time, etc.

• The rate of change in velocity is called acceleration. Its SI unit is m/s2.

• The inability of a body to change its state (rest or motion) by itself is called
inertia. It is of two types, viz. inertia of rest and inertia of motion.

• Inertia of rest is the inability of a body at rest to change its state of rest by itself.

• Inertia of motion is the inability of a moving body in a straight path to change
its state of motion by itself.

• According to Newton's first law of motion, "Every body continues to be in a
state of rest or of uniform motion in a straight line unless an external force is
applied on it."

• The momentum of a body can be defined as the product of its mass and velocity.

• According to Newton's second law of motion, "Acceleration produced on
a body is directly proportional to the force applied on it and is inversely
proportional to its mass."

• According to Newton's third law of motion, "To every action, there is equal but
opposite reaction."

• A force can give energy to an object causing the object to start moving, stop
moving or change its motion.

36 Oasis School Science - 9 PHYSICS

Exercise

Group-A
1. What is force? Write down its SI unit.
2. Define 1N force. Write down CGS unit of force.
3. What is inertia?
4. What inertia of rest? Write with an example.
5. Define inertia of motion with any one examples.
6. On which factor does the inertia of a body depend? Write.
7. What is the relation between the mass and inertia of a body?
8. What is speed? Write down its formula.
9. What is a scalar quantity?
10. Define vector quantity with any one example.
11. `What is displacement? Write its SI unit.
12. What is average velocity? How is it calculated?
13. What is acceleration? Write down its unit in SI system.
14. What is retardation? In which condition is it possible?
15. Define equations of motion?
16. Define retardation. In which unit is it measured?
17. State Newton's second law of motion.
18. State Newton's third law of motion.
19. "Every action has equal but opposite reaction." Which law of Newton is stated by this

statement?
20. What is velocity-time graph?
21. Which factors does the inertia of rest depend on? Write.
22. What is the relationship between Newton's first law of motion and inertia?
23. What is the relationship among initial velocity, distance covered, acceleration produced

and final velocity of a moving body?
24. Give one example which describes Newton's first law of motion.
25. Give one example which describes Newton's third law of motion.
26. What is balanced force? Give one example.
27. What is unbalanced force? Give one example.

PHYSICS Oasis School Science - 9 37

Group-B
1. Write any two differences between vectors and scalars.
2. Speed is called a scalar quantity but velocity is called a vector quantity, why?
3. Write any two differences between distance and displacement.
4. Write any two differences between acceleration and retardation.
5. Blades of a running electric fan continue to spin for some time even after the electricity

is switched off. Why?
6. When a carpet is beaten with a stick, the dust particles fall off. Give reason.
7. It is dangerous to jump out of a moving vehicle. Why?
8. The passengers standing on a stationary bus fall backward when the bus suddenly

moves forward. Give reason.
9. An athlete runs some distance before taking a long jump. Why?
10. A gun recoils while firing a bullet. Give reason.
11. A batsman often ducks to a bouncer. Why?
12. When we jump out of a boat, the boat moves slightly backward. Give reason.
13. We can catch a rolling ball but not a flying bullet. Why?
14. A cricket player lowers his hands while catching the ball. Give reason.

Group-C

1. What is distance-time graph? Draw a distance-time graph to represent a body moving
with uniform speed.

2. What is velocity-time graph? Draw a velocity-time graph to represent a body moving
with uniform acceleration.

3. Draw the graphical plot to describe the following motion.

i) A body at rest

ii) A body moving with non-uniform acceleration

4. Prove that: v = u + at

5. Prove that : F = ma

6. State Newton's third law of motion with an example. It is also called the law of action
and reaction. Why?

7. Prove that : v2 = u2 + 2as

8. If a body starts from rest and attains a velocity of 20 m/s in 8 seconds, find the acceleration

produced on the body. [Ans: 2.5 m/s2]

9. A vehicle is running at a speed of 45 km/h. If it is stopped in 3 seconds by applying the

brakes, calculate the retardation of the vehicle and the distance travelled before it stops.

[Ans: 4.16 m/s2, 18.75 m]

38 Oasis School Science - 9 PHYSICS

10. The velocity of a moving body increases from 10 m/s to 15 m/s in 5 seconds. Calculate its

acceleration. [Ans:1m/s2]

11. A body moving along a straight path at a velocity of 20 m/s attains an acceleration of

4 m/s2. Calculate the velocity of the body after 2 seconds. [Ans: 28 m/s]

12. A body of mass 10 kg is pulled by a force of 8N. Calculate the acceleration and the final

velocity of the body after 5 seconds. [Ans: 0.8 m/s2, 4 m/s]

Group-D

1. A car was moving at a speed of 90 km/h. On seeing a baby 20 m ahead on the road,

the driver jammed on the brakes and it came to rest at a distance of 15m. What is its

retardation and how long does it take to come at rest? [Ans: 20.83 m/s2, 1.2 s]

2. Study the given graph and answer the following questions :

Velocity (m/s)15 A B

10

5 D EC

05 10 15

Time (s)

i) Name the type of the motion represented by OA, AB and BC.

ii) Calculate the acceleration. [Ans: 3 m/s2]
iii) Calculate the retardation. [Ans: 3 m/s2

3. A body starts moving from rest and attains the acceleration of 0.5 m/s2. Calculate the
velocity at the end of 3 minutes and also find the distance travelled by it during that
time. [Ans: 90 m/s, 8100m]

4. A car weighing 1600 kg is accelerated to 30m/s from start in 20s. Calculate the
acceleration of the car and the magnitude of the force applied. [Ans: a = 1.5m/s2, F = 2400N]

5. Calculate the momentum of a truck of mass 25000 kg when [Ans: 0]
i) it is at rest. [Ans: 625000 kg m/s]

ii) it is moving with a uniform velocity of 90 km/h.

PHYSICS Oasis School Science - 9 39

3UNIT Estimated teaching periods

Theory 5

Practical 2

Simple Machines

Objectives Archimedes

After completing the study of this unit, students will be able to:

• describe different types of simple machines (lever, pulley, inclined plane, wheel
and axle, screw and wedge.

• define MA, VR and efficiency related to different simple machines.

• solve the numerical problems related to simple machines.

• explain the moment in lever with a labelled diagram.

3.1 Introduction

We use a variety of machines in our daily life. Machines help us to perform mechanical
work by using muscular energy. A device which makes our work easier, faster and more
convenient is called a machine. We can do various works with the help of different machines.
Some machines are simple in structure while others are complex. Those machines which are
simple in structure are called simple machines. A particular simple machine helps us to do
a particular work only. The devices which are used to make our work easier, faster and to
change the direction of force are called simple machines. For example, scissors, crow bar,
beam balance, fire tongs, pulley, knife, etc. Simple machines are very useful to us because they
help to multiply the force, apply force in a convenient direction, apply force at a convenient
point and to gain speed.

Scissors Beam balance Wheel barrow Pulley Screw Axe

Fig. 3.1 Some simple machines

3.2 Applications of Simple Machines

1. Simple machines help to multiply force.
2. They help to change the direction of force.
3. They help to increase the speed of work.
4. They help to do work safely.

convenient /kənˈviːnɪənt/ - useful, easy or quick to do, not causing problems

40 Oasis School Science - 9 PHYSICS

3.3 Mechanical Advantage (MA)

Simple machines are used to do various works. To do any work, force should be applied to a
machine. The force which is applied to a machine is called effort and the resistance that is to
be overcome by the applied force is called the load. The ratio of the load to the effort is called
mechanical advantage, i.e.

MA = Load (L)
Effort (E)

Since mechanical advantage is the ratio of two similar quantities, i.e. forces, it has no unit.
If the load lifted by a machine is greater than the effort applied, the mechanical advantage
is greater than 1 (MA>1). If the load lifted is less than the effort applied, the MA is less than
1 [MA<1]. MA depends on friction and the weight of a machine. If friction increases, MA
decreases. No machine is frictionless. Due to the presence of friction, large amount of effort
is wasted. Similarly, due to the weight of a machine, the mechanical advantage becomes less.

3.4 Velocity Ratio (VR)

If an effort is applied to a machine, both load and effort move. Generally, the machines are
designed in such a way that the effort moves more than the load.

Velocity ratio is the ratio of the distance travelled by effort to the distance travelled by load.

VR = Distance travelled by effort = Effort distance
Distance travelled by load Load distance


VR of a machine is not affected by the friction or weight of the machine. It has no unit since it
is the ratio of two similar quantities, i.e. distance.

3.5 Efficiency (ŋ)

The work done by a machine is called output work. It is the product of load and the distance
travelled by load. Similarly, the work done on a machine is called input work. It is the product
of effort and the distance travelled by effort, i.e.

Output work = load × distance travelled by load
Input work = effort × distance travelled by effort

The percentage ratio of output work to input work is called efficiency of a machine. It is
expressed in percentage and denoted by the letter eta (ŋ).

Efficiency (ŋ) = Output work × 100%
Input work

PHYSICS Oasis School Science - 9 41

3.6 Relation among MA, VR and ŋ

Efficiency (ŋ) = Output work × 100%
Input work

= Load×distance travelled by load × 100%
Effort×distance travelled by effort
Fact File-1
Load
The efficiency of a simple machine
= Effort × 100% is 85% means that the simple
Distance travelled by effort machine converts 85% of input
work into the useful output work
Distance travelled by load

= MA × 100% and 15% of input work is wasted
VR to overcome the friction between
the moving parts of the machine
and to over come the weight of
∴ ŋ = MA × 100% the machine.
VR


This is the required relation among MA, VR and ŋ.

Efficiency of a machine can also be defined as the percentage ratio of mechanical advantage
(MA) to the velocity ratio (VR) of the machine. Efficiency is the ratio of two works done. So, it
has no unit. MA and ŋ are affected by the friction but not VR. So, MA is always less than VR
and the efficiency of a machine can be increased by reducing the friction. Some of the ways to
reduce friction are using grease, ball-bearings, making the surface smooth, etc.

3.7 Ideal Machine

The machine without any friction during its operation is called an ideal (or perfect) machine.
In such a machine, the output work is always equal to the input work.

For an ideal machine,

Output work = Input work

Also, = Output work × 100 %
ŋ Input work

= 100% [∵ output work = input work]

Thus, ideal machine has 100% efficiency. It is to be noted that in practice no machine is 100%
efficient. The output work of a machine is always less than the input work. A machine cannot
be 100% efficient because of the following reasons:

(i) A part of the work done or energy supplied to the machine is wasted in overcoming the
friction between the movable parts of the machine.

(ii) A part of work done or energy supplied to the machine is wasted in moving the parts
of the machine. Please note that no machine is weightless. Therefore, the efficiency of a
practical machine is always less than 100%.

ideal /aɪˈdɪəl/ - perfect, most suitable

42 Oasis School Science - 9 PHYSICS