This book has been revised according to the CCE pattern of school education based onNCERT syllabus prescribed by the Central Board of Secondary Education (CBSE) for Class IX

Science for Ninth Class(Part – 1)

PhysicsAs per NCERT/CBSE Syllabus

(Based on CCE Pattern of School Education)

Lakhmir SinghAnd

Manjit Kaur

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© 1980, Lakhmir Singh & Manjit Kaur

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Physics IX: Lakhmir Singh

LAKHMIR SINGH did his M.Sc. from DelhiUniversity in 1969. Since then he has beenteaching in Dyal Singh College of DelhiUniversity, Delhi. He started writing books in1980. Lakhmir Singh believes that bookwriting is just like classroom teaching. Thougha book can never replace a teacher but it shouldmake the student feel the presence of a teacher.Keeping this in view, he writes books in sucha style that students never get bored readinghis books. Lakhmir Singh has written morethan 15 books so far on all the science subjects:Physics, Chemistry and Biology. He believesin writing quality books. He does not believein quantity.

MANJIT KAUR did her B.Sc., B.Ed. fromDelhi University in 1970. Since then she hasbeen teaching in a reputed school ofDirectorate of Education, Delhi. Manjit Kauris such a popular science teacher that all thestudents want to join those classes which sheteaches in the school. She has a vast experienceof teaching science to school children, and sheknows the problems faced by the children inthe study of science. Manjit Kaur has put allher teaching experience into the writing ofscience books. She has co-authored more than15 books alongwith her husband, LakhmirSingh.

It is the team-work of Lakhmir Singh andManjit Kaur which has given some of the mostpopular books in the history of scienceeducation in India. Lakhmir Singh and ManjitKaur both write exclusively for the mostreputed, respected and largest publishinghouse of India : S.Chand and Company Pvt.Ltd.

ABOUT THE AUTHORS

An Open LetterDear Friend,

We would like to talk to you for a few minutes, just to giveyou an idea of some of the special features of this book.Before we go further, let us tell you that this book has beenrevised according to the NCERT syllabus prescribed by theCentral Board of Secondary Education (CBSE) based on new“Continuous and Comprehensive Evaluation” (CCE) pattern ofschool education. Just like our earlier books, we have writtenthis book in such a simple style that even the weak studentswill be able to understand physics very easily. Believe us,while writing this book, we have considered ourselves to bethe students of Class IX and tried to make things as simpleas possible.

The most important feature of this revised edition of the book isthat we have included a large variety of different types ofquestions as required by CCE for assessing the learning abilitiesof the students. This book contains :

(i) Very short answer type questions (including true-false typequestions and fill in the blanks type questions),

(ii) Short answer type questions,

(iii) Long answer type questions (or Essay type questions),

(iv) Multiple choice questions (MCQs) based on theory,

(v) Questions based on high order thinking skills (HOTS),

(vi) Multiple choice questions (MCQs) based on practical skillsin science,

(vii) NCERT book questions and exercises (with answers), and

(viii) Value based questions (with answers).

Please note that answers have also been given for the varioustypes of questions, wherever required. All these features willmake this book even more useful to the students as well as theteachers. “A picture can say a thousand words”. Keeping this inmind, a large number of coloured pictures and sketches ofvarious scientific processes, procedures, appliances,manufacturing plants and everyday situations involving principlesof physics have been given in this revised edition of the book.This will help the students to understand the various concepts ofphysics clearly. It will also tell them how physics is applied in thereal situations in homes, transport and industry.

We are sure you will agree with us that the facts andformulae of physics are just the same in all the books, thedifference lies in the method of presenting these facts tothe students. In this book, the various topics of physicshave been explained in such a simple way that whilereading this book, a student will feel as if a teacher issitting by his side and explaining the various things tohim. We are sure that after reading this book, the studentswill develop a special interest in physics and they wouldlike to study physics in higher classes as well.

We think that the real judges of a book are the teachersconcerned and the students for whom it is meant. So, werequest our teacher friends as well as the students topoint out our mistakes, if any, and send their commentsand suggestions for the further improvement of this book.

Wishing you a great success,

Yours sincerely,

396, Nilgiri Apartments,Alaknanda, New Delhi-110019E-mail : singhlakhmir@hotmail.com

Other Books by Lakhmir Singh and Manjit Kaur

1. Awareness Science for Sixth Class

2. Awareness Science for Seventh Class

3. Awareness Science for Eighth Class

4. Science for Ninth Class (Part 2) CHEMISTRY

5. Science for Tenth Class (Part 1) PHYSICS

6. Science for Tenth Class (Part 2) CHEMISTRY

7. Science for Tenth Class (Part 3) BIOLOGY

8. Rapid Revision in Science

(A Question-Answer Book for Class X)

9. Science for Ninth Class (J & K Edition)

10. Science for Tenth Class (J & K Edition)

11. Science for Ninth Class (Hindi Edition) :

PHYSICS and CHEMISTRY

12. Science for Tenth Class (Hindi Edition) :

PHYSICS, CHEMISTRY and BIOLOGY

13. Saral Vigyan (A Question-Answer Science

Book in Hindi for Class X)

DISCLAIMERWhile the authors of this book have made every effort to avoid any mistake or omission and have used their skill,expertise and knowledge to the best of their capacity to provide accurate and updated information, the authors and thepublisher do not give any representation or warranty with respect to the accuracy or completeness of the contents of thispublication and are selling this publication on the condition and understanding that they shall not be made liable in anymanner whatsoever. The publisher and the authors expressly disclaim all and any liability/responsibility to any person,whether a purchaser or reader of this publication or not, in respect of anything and everything forming part of thecontents of this publication. The publisher and authors shall not be responsible for any errors, omissions or damagesarising out of the use of the information contained in this publication. Further, the appearance of the personal name,location, place and incidence, if any; in the illustrations used herein is purely coincidental and work of imagination. Thusthe same should in no manner be termed as defamatory to any individual.

CONTENTSFIRST TERM

1. MOTION 1 – 44Movement of a Body (or Object) is Called Motion ; Distance Travelled andDisplacement ; Uniform Motion and Non-Uniform Motion ; Speed ;Average Speed and Uniform Speed (or Constant Speed) ; Numericals onSpeed ; Velocity ; Uniform Velocity (or Constant Velocity) ; Speed andVelocity are Not Always Equal in Magnitude ; Numericals on Velocity ;Acceleration ; Uniform Acceleration and Non-Uniform Acceleration ;Retardation (Deceleration or Negative Acceleration) ; Average Velocity ;Equations of Uniformly Accelerated Motion : First Equation of Motion,Second Equation of Motion and Third Equation of Motion ; Numericals onUniformly Accelerated Motion ; Graphical Representation of Motion ;Distance - Time Graphs and Speed-Time Graphs (or Velocity - TimeGraphs) ; Speed - Time Graph When Speed Remains Constant ; Speed -Time Graph When Speed Changes at a Uniform Rate (UniformAcceleration) ; Speed - Time Graph When the Initial Speed of the Body isNot Zero ; Speed - Time Graph When Speed Changes at a Non-UniformRate (Non-Uniform Acceleration) ; Numericals Based on Graphs ; To Derivethe Equations of Motion by Graphical Method ; Uniform Circular Motion ;Examples of Uniform Circular Motion : Motion of Satellites Around theEarth, Motion of Earth Around the Sun, Motion of Athlete on Circular Trackand Motion of Seconds’ Hand of a Watch on Dial ; To Calculate the Speedof a Body Moving in Uniform Circular Motion

2. FORCE AND LAWS OF MOTION 45 – 77A Push or Pull on a Body is Called Force ; Effects of Force : A Force CanMove a Stationary Body, A Force Can Stop a Moving Body, A Force CanChange the Speed of a Moving Body, A Force Can Change the Directionof a Moving Body and a Force Can Change the Shape (and Size) of aBody ; Balanced Forces and Unbalanced Forces ; Newton’s Laws ofMotion ; Newton’s First Law of Motion and Inertia of Bodies (or Objects) ;

Momentum : A Measure of the Quantity of Motion Possessed by a MovingBody ; Momentum Depends on Mass and Velocity of a Moving Body ;Numericals Based on Momentum; Newton’s Second Law of Motion ;Applications of Newton’s Second Law of Motion : Catching a Cricket Ball,The Case of a High Jumper and the Use of Seat Belts in Cars ; NumericalsBased on Newton’s Second Law of Motion ; Newton’s Third Law of Motion ;Action and Reaction Act on Two Different Bodies ; Some Examples toIllustrate Newton’s Third Law of Motion : How Do We Walk, Why the GunRecoils, The Flying of Jet Aeroplanes and Rockets, The Case of a Boatand the Ship, The Case of Hose Pipe and the Case of Horse Pulling aCart ; Conservation of Momentum ; Law of Conservation of Momentum ;Applications of the Law of Conservation of Momentum ; Recoil Velocity ofa Gun ; Numericals Based on the Conservation of Momentum

3. GRAVITATION 78 – 128Every Object in the Universe Attracts Every Other Object ; Universal Law

of Gravitation ; Gravitational Constant (G) ; Units of Gravitational Constant ;

Value of Gravitational Constant ; Gravitational Force Between Objects of

Small Size and Big Size ; Gravitational Force Holds the Solar System

Together ; Kepler’s Laws of Planetary Motion ; How Did Newton Guess

the Inverse Square Law ; Newton’s Third Law of Motion and Gravitation ;

Free Fall and Freely Falling Bodies ; Acceleration Due to Gravity (g) ;

Calculation of Acceleration Due to Gravity ; Variation of Acceleration Due

to Gravity ; Acceleration Due to Gravity Does Not Depend on Mass of the

Body ; Equations of Motion For Freely Falling Bodies ; Mass and Weight ;

Weight of an Object on the Moon ; To Show That the Weight of an Object

on the Moon is 1/6th of its Weight on the Earth ; Thrust and Pressure ;

Explanation of Some Everyday Observations on the Basis of Pressure ;

Pressure in Fluids (Liquids and Gases) ; Buoyancy ; Buoyant Force and

Cause of Buoyant Force ; Experiment to Study the Magnitude of Buoyant

Force; Factors Affecting Buoyant Force ; Archimedes’ Principle and

Applications of Archimedes’ Principle ; Why Objects Float or Sink in a

Liquid ; The Principle of Flotation ; How Does a Boat Float in Water; The

Density of Floating Objects ; Why Ships Float ; Density and Relative Density

SECOND TERM

4. WORK AND ENERGY 129 – 165Work is Done When a Force Produces Motion ; Unit of Work : Joule ; WorkDone Against Gravity ; Numericals on Work ; Work Done by a Force ActingObliquely ; Formula for Work Done When a Body Moves at an Angle tothe Direction of Force ; Work Done When the Force Acts at Right Angles tothe Direction of Motion ; Work Done When the Force Acts Opposite to theDirection of Motion ; Positive Work, Negative Work and Zero Work ; Energyis the Ability to Do Work ; Unit of Energy : Joule ; Different Forms of Energy :Kinetic Energy, Potential Energy, Chemical Energy, Heat Energy, LightEnergy, Sound Energy, Electrical Energy and Nuclear Energy ; KineticEnergy : Energy Due to Motion of a Body ; Formula for Kinetic Energy ;Potential Energy : Energy Due to Higher Position or Change in Shape of aBody ; Gravitational Potential Energy and Elastic Potential Energy ; Formulafor Gravitational Potential Energy ; Power : Rate of Doing Work ; Unit ofPower : Watt ; Commercial Unit of Energy : Kilowatt - hour (kWh) ; RelationBetween Kilowatt - Hour and Joule ; Transformation of Energy ; EnergyTransformations at a Hydroelectric Power House and a Thermal PowerHouse ; Using Energy Converters : Electric Motor, Electric Iron, ElectricBulb, Radio, Steam Engine, Car Engine, Cell (or Battery), Gas Stove, SolarWater Heater and Solar Cell ; Law of Conservation of Energy ; Conservationof Energy During the Free Fall of a Body and in a Simple Pendulum

5. SOUND 166 – 211Sound is a Form of Energy ; Sound Travels in the Form of Waves ;Longitudinal Waves and Transverse Waves; Sound Waves are LongitudinalWaves ; Graphical Representation of Longitudinal Sound Waves ;Characteristics of a Sound Wave : Wavelength, Amplitude, Time - Period,Frequency, Velocity of Wave (or Speed of Wave) ; Relationship BetweenVelocity, Frequency and Wavelength of a Wave ; Production of Sound byVibrating Objects : Vibrating Strings, Vibrating Air Columns, VibratingMembranes and Vibrating Plates ; Sound Waves in Air ; Propagation ofSound (or Transmission of Sound) ; Sound Needs a Material Medium toTravel ; Sound Can Travel Through Solids, Liquids and Gases ; SoundCannot Travel Through Vacuum ; The Case of Moon and Outer Space ;

The Speed of Sound ; Sonic Boom ; The Race Between Sound and Light ;Reflection of Sound ; Laws of Reflection of Sound ; Applications of Reflectionof Sound : Megaphone, Bulb Horn, Stethoscope and Soundboard ; Echo :A Reflected Sound ; Calculation of Minimum Distance to Hear an Echo ;Reverberations ; Methods of Reducing Excessive Reverberations in BigHalls and Auditoriums ; The Frequency Range of Hearing in Humans ;Audible Sound, Infrasonic Sound and Ultrasonic Sound ; Applications ofUltrasound ; Sonar ; Finding the Depth of Sea and Locating Shoal of Fish,Shipwrecks and Enemy Submarines by Using Sonar; Characteristics ofSound : Loudness, Pitch and Quality (or Timbre) ; The Human Ear :Construction and Working ; Care of Ears

• Multiple Choice Questions (MCQs) Based on Practical Skills in Science (Physics) 212 – 216

• NCERT Book Questions and Exercises (with answers) 217 – 262

• Value Based Questions (with answers) 263 – 276

LATEST CBSE SYLLABUS CLASS 9 SCIENCE(PHYSICS PART)

FIRST TERM(April to September)

Motion : Distance and displacement ; Velocity ; Uniform and non-uniform motion along a straightline ; Acceleration ; Distance-time and velocity-time graphs for uniform motion and uniformly acceleratedmotion ; Equations of motion by graphical method ; Elementary idea of uniform circular motion

Force and Newton’s Laws : Force and motion ; Newton’s laws of motion ; Inertia of a body ; Inertiaand mass ; Momentum ; Force and acceleration ; Elementary idea of conservation of momentum ; Actionand reaction forces

Gravitation : Gravitation ; Universal law of gravitation ; Force of gravitation of the earth (gravity) ;Acceleration due to gravity ; Mass and Weight ; Free fall

SECOND TERM(October to March)

Flotation : Thrust and pressure ; Archimedes’ principle; Buoyancy; Elementary idea of relative densityWork, energy and power : Work done by a force ; Energy ; Power ; Kinetic energy and potential

energy ; Law of conservation of energySound : Nature of sound and its propagation in various media ; Speed of sound ; Range of hearing in

humans ; Ultrasound ; Reflection of sound ; Echo and SONAR ; Structure of the human ear (auditoryaspect only)

Atree is fixed at a place, so we say that it is stationary. Similarly, a house, a school, a factory, electricpoles and telephone poles are all stationary objects which remain fixed at a place. On the otherhand, a man, animals, birds, cars, buses, trains, ships and aeroplanes, etc., do not remain stationary

all the time. They can move from one place to another. For example, a man moves when he walks along aroad, a bird moves when it flies in the sky, a cheetah moves when it runs in the jungle, and a fish moveswhen it swims in water. Similarly, a car or bus moves on a road, a train moves on the track, a ship moves

in water and an aeroplane moves when it flies in air from one place to another. The movement of a body(or object) is called motion. A common characteristic of all the moving bodies is that they change theirposition with time. We can now define motion as follows :

A body is said to be in motion (or moving) when its position changes continuously with respect to astationary object taken as reference point. For example, when the position of a car changes continuouslywith respect to stationary objects like houses and trees, etc., we say that the car is moving or that the car isin motion. Let us take an example to understand the meaning of motion more clearly.

MOTION

Figure 1. All the vehicles seen in this photograph are moving on the road. They are in motion.

1

Science for Ninth Class Part 1 Physics

Publisher : SChand Publications ISBN : 9789352530250Author : Lakhmir Singh &Manjit Kaur

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