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      Class 9 Science

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      • Class 09
      • Class 9 Science
      CoursesClass 09ScienceClass 9 Science
      • 01.Matter in Our Surroundings
        9
        • Lecture1.1
          Matter and Its Properties 39 min
        • Lecture1.2
          States of Matter and Compressibility & Rigidity 21 min
        • Lecture1.3
          Moving through, Fluidity, Density, Diffusion, Pressure 26 min
        • Lecture1.4
          Change of State of Matter 56 min
        • Lecture1.5
          Evaporation and Boiling 39 min
        • Lecture1.6
          Cooling Effect of Evaporation Two More States of Matter 22 min
        • Lecture1.7
          Chapter Notes – Matter in Our Surroundings
        • Lecture1.8
          NCERT Solutions – Matter in Our Surroundings
        • Lecture1.9
          Revision Notes Matter in Our Surroundings
      • 02.Is Matter Around Us Pure
        9
        • Lecture2.1
          Elements and Compounds 20 min
        • Lecture2.2
          Mixtures, Homogeneous & Heterogeneous and Chemical & Physical Change 37 min
        • Lecture2.3
          Solution, Suspension, Colloid and Tyndal Effect 48 min
        • Lecture2.4
          Terms related to Solution and Solubility 42 min
        • Lecture2.5
          Separation of Mixtures 47 min
        • Lecture2.6
          Cleaning Drinking Water and Classification of Matter 29 min
        • Lecture2.7
          Chapter Notes – Is Matter Around Us Pure
        • Lecture2.8
          NCERT Solutions – Is Matter Around Us Pure
        • Lecture2.9
          Revision Notes Is Matter Around Us Pure
      • 03.Atoms and Molecules
        7
        • Lecture3.1
          Atom and its Properties, Atomic Mass, Molecule and Molecular Mass 40 min
        • Lecture3.2
          Ions, Valency and Writing the formulae of Compounds 47 min
        • Lecture3.3
          Mole Concept 42 min
        • Lecture3.4
          Calculation of no. of Moles, Percentage of an Element in a Compound and Laws of Chemical Combination 30 min
        • Lecture3.5
          Chapter Notes – Atoms and Molecules
        • Lecture3.6
          NCERT Solutions – Atoms and Molecules
        • Lecture3.7
          Revision Notes Atoms and Molecules
      • 04.Structure of The Atom
        7
        • Lecture4.1
          Charged Particles in Matter and Discovery of Sub – atomic Particles 31 min
        • Lecture4.2
          Atomic Model by J.J Thomson’s Model and Rutherford 57 min
        • Lecture4.3
          Ion, Mass Number, Isotopes, Isobar and Fractional Mass number of Elements 01 hour
        • Lecture4.4
          Electron Distribution in Orbits and Valency 01 hour
        • Lecture4.5
          Chapter Notes – Structure of The Atom
        • Lecture4.6
          NCERT Solutions – Structure of The Atom
        • Lecture4.7
          Revision Notes Structure of The Atom
      • 05.Cell - Fundamental Unit of Life
        7
        • Lecture5.1
          Introduction to Cell and Its Structure – Cell Wall 31 min
        • Lecture5.2
          Cell Membrane, Cytoplasm, Nucleus 32 min
        • Lecture5.3
          Ribosomes, Endoplasmic Reticulum, Golgi bodies, Lisosomes, Mitocondria 38 min
        • Lecture5.4
          Plastids, Vacuole; Types of Cell and Transport through Plasma Membrane 33 min
        • Lecture5.5
          Chapter Notes – Cell – Fundamental Unit of Life
        • Lecture5.6
          NCERT Solutions – Cell – Fundamental Unit of Life
        • Lecture5.7
          Revision Notes Cell – Fundamental Unit of Life
      • 06.Tissues
        8
        • Lecture6.1
          Division of Labour, Plant Tissues – Merismatic Tissue 20 min
        • Lecture6.2
          Plant Tissue-Permanent Tissue: Simple Permanent Tissue 34 min
        • Lecture6.3
          Plant Tissue-Permanent Tissue: Complex and Protective Tissue 31 min
        • Lecture6.4
          Animal Tissue- Muscular Tissue and Nervous Tissue 27 min
        • Lecture6.5
          Animal Tissue- Connective Tissue and Epithelial Tissue 42 min
        • Lecture6.6
          Chapter Notes – Tissues
        • Lecture6.7
          NCERT Solutions – Tissues
        • Lecture6.8
          Revision Notes Tissues
      • 07.Diversity in Living Organisms
        8
        • Lecture7.1
          Introduction to Biodiversity and Classification, Nomenclature 35 min
        • Lecture7.2
          The Five Kingdoms 29 min
        • Lecture7.3
          Plantae Kingdom 42 min
        • Lecture7.4
          Animalia Kingdom 01 hour
        • Lecture7.5
          Classification of Chordates and Revision of Animalia Kingdom 33 min
        • Lecture7.6
          Chapter Notes – Diversity in Living Organisms
        • Lecture7.7
          NCERT Solutions – Diversity in Living Organisms
        • Lecture7.8
          Revision Notes Diversity in Living Organisms
      • 08.Motion
        11
        • Lecture8.1
          Straight Line Motion, Position, Vector and Scalar; 23 min
        • Lecture8.2
          Distance & Displacement 48 min
        • Lecture8.3
          Speed and Velocity 57 min
        • Lecture8.4
          Acceleration and Deacceleration, Uniform & Non-uniform Acceleration 47 min
        • Lecture8.5
          Equations of Uniformly Accelerated Motion 58 min
        • Lecture8.6
          Uniform Circular Motion 30 min
        • Lecture8.7
          Graphical representation of Motion 30 min
        • Lecture8.8
          Calculations Using Graph 28 min
        • Lecture8.9
          Chapter Notes – Motion
        • Lecture8.10
          NCERT Solutions – Motion
        • Lecture8.11
          Revision Notes Motion
      • 09.Force and Newtons Laws of Motion
        12
        • Lecture9.1
          Force and Net or Resultant Force 46 min
        • Lecture9.2
          Newton’s 1st Law 46 min
        • Lecture9.3
          Momentum 46 min
        • Lecture9.4
          Newton’s 2nd Law 27 min
        • Lecture9.5
          Newton’s 2nd Law in Terms of Acceleration; 42 min
        • Lecture9.6
          Newton’s 1st Law from 2nd law and Practical Examples of Newton’s 2nd Law 42 min
        • Lecture9.7
          Newton’s 3rd Law and its Practical Examples 35 min
        • Lecture9.8
          Conservation of Momentum 33 min
        • Lecture9.9
          Practical Applications of Conservation of Momentum 29 min
        • Lecture9.10
          Chapter Notes – Force and Newtons Laws of Motion
        • Lecture9.11
          NCERT Solutions – Force and Newtons Laws of Motion
        • Lecture9.12
          Revision Notes Force and Newtons Laws of Motion
      • 10.Gravitation
        9
        • Lecture10.1
          Universal Law of Gravitation and Free Fall 41 min
        • Lecture10.2
          Falling Bodies: case 1 46 min
        • Lecture10.3
          Falling bodies: case 2 and Air Resistance 42 min
        • Lecture10.4
          Value of g, Mass and Weight, Weight on Moon, Circular Motion and Gravitation 48 min
        • Lecture10.5
          Thrust and Pressure and Pressure in fluids 37 min
        • Lecture10.6
          Archimedes Principle; Density 37 min
        • Lecture10.7
          Chapter Notes – Gravitation
        • Lecture10.8
          NCERT Solutions – Gravitation
        • Lecture10.9
          Revision Notes Gravitation
      • 11.Work and Energy
        7
        • Lecture11.1
          Work and Workdone Against Gravity, Oblique Displacement 01 hour
        • Lecture11.2
          Energy and Different Forms of Energy, Derivation of Formulae of K.E. 58 min
        • Lecture11.3
          Transformation of Energy and Law of Conservation of Energy 01 hour
        • Lecture11.4
          Rate of doing Work and Commercial Unit of Energy 43 min
        • Lecture11.5
          Chapter Notes – Work and Energy
        • Lecture11.6
          NCERT Solutions – Work and Energy
        • Lecture11.7
          Revision Notes Work and Energy
      • 12.Sound
        8
        • Lecture12.1
          Production and Propagation of Sound and Medium for Sound 30 min
        • Lecture12.2
          Frequency and Velocity of Sound Wave, Characteristic of Sound 01 hour
        • Lecture12.3
          Sonic Boom, Light faster than Sound, Reflection of Sound, Echo and Reverberation 56 min
        • Lecture12.4
          Types of Sound Based on Frequency 42 min
        • Lecture12.5
          Human Ear and Intensity of Sound 25 min
        • Lecture12.6
          Chapter Notes – Sound
        • Lecture12.7
          NCERT Solutions – Sound
        • Lecture12.8
          Revision Notes Sound
      • 13.Why do We Fall Ill
        7
        • Lecture13.1
          Factors Determining Health, Disease, Look of Disease, Cause of Disease, Types of Diseases 24 min
        • Lecture13.2
          Infectious Diseases, Immune System, Treatment of Diseases 55 min
        • Lecture13.3
          Prevention from Disease, Vaccination – Immunisation 36 min
        • Lecture13.4
          AIDS, Different Modes for Different Diseases 18 min
        • Lecture13.5
          Chapter Notes – Why do We Fall Ill
        • Lecture13.6
          NCERT Solutions – Why do We Fall Ill
        • Lecture13.7
          Revision Notes Why do We Fall Ill
      • 14.Natural Resources
        7
        • Lecture14.1
          Natural Resource-Air and its Pollution 57 min
        • Lecture14.2
          Natural Resource-Water and Soil and its Pollution 49 min
        • Lecture14.3
          Biogeochemical Cycles 33 min
        • Lecture14.4
          Green House Effect, Global Warming and Ozone Layer Depletion 30 min
        • Lecture14.5
          Chapter Notes – Natural Resources
        • Lecture14.6
          NCERT Solutions – Natural Resources
        • Lecture14.7
          Revision Notes Natural Resources
      • 15.Improvements in Food Resources
        7
        • Lecture15.1
          Various Revolution Held in India; Types of Crops; Crop Season; Crop Variety Improvement 31 min
        • Lecture15.2
          Crop Production Improvement 45 min
        • Lecture15.3
          Crop Protection Improvement and Organic Farming 29 min
        • Lecture15.4
          Animal Husbandry 40 min
        • Lecture15.5
          Chapter Notes – Improvements in Food Resources
        • Lecture15.6
          NCERT Solutions – Improvements in Food Resources
        • Lecture15.7
          Revision Notes Improvements in Food Resources

        Chapter Notes – Work and Energy

        Work and Energy

        Work

        Work is defined as product of force and displacement in the direction of force.

        Work is done when we swim, work is done we lift water from well, etc. Work done is denoted by a letter ‘W’.

        W=F × s

        Here,

        W = Work done on an object

        F = Force on the object

        s = Displacement of the object

        The unit of Work is Newton metre (Nm) or joule (J).

        1 Joule is defined as the amount of work done by force of 1N when displacement is 1m.

        • When both the force and the displacement are in the same direction, positive work is done.

        W = F x s

        • When force acts in a direction opposite to the direction of displacement, the work done is negative.

        W = (-F) x s or W = F x (-s)

        Angle between force and displacement is 180o.

        • When either force or displacement is zero, then work done is said to be zero. Also if force and displacement act an angle of 90o then also work done is zero.

        For examples:

        1. The man applies force on wall but displacement is zero so no work is done.
          https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS3oKUfzM0UyytxDSUjY7O_rqWZUbtN9CGvHcPF2ps7FVGojgSZnA
        2. In below picture force and displacement are perpendicular to each other so here also work done is zero.

        Sign of work done by gravity

        Let us consider an example where a man throws a ball up in air, then

        • When ball is going up its displacement is upwards and gravitational force is
        • acting upwards. So, displacement and force are in opposite direction therefore work done is negative.
        • And when ball is coming downwards its displacement and gravitational force are both acting downwards. So, displacement and force are in same direction therefore work done is positive.

        Work done against Gravity

        Whenever an object is lifted against gravity then the amount of work done in lifting the object is called as work done against gravity.

        Note – When we lift an object against gravity, we have to apply force equal to weight of object.

        For example; when we lift an object from ground and put in a table then

        • Work done by gravity will be negative because displacement of object is upwards and gravitational force is acting downwards.
        • Work done against gravity is positive because it is the force of our which is acting against gravity in upward direction and also displacement is upwards.

         

        Oblique Displacement (Advance Topic)

        • In this case force and displacement make some angle with each other.
        • When displacement and force make some angle between them, we use displacement in direction of force for work calculation.
        • In this case force and displacement act an angle to each other.

        Workdone by gravity = Force due to gravity displacement in direction of force
        D:\Diagrams\slope.jpg

        Energy

        • Energy is ability to do work.
        • Energy possessed by an object is the amount of work it can do.
        • If an object can do more work, it has more energy and vice versa.

        For example; a raised hammer can do work so it has energy and similarly a bomb can do work so it has also energy, a running bike can do work so it has energy, etc.

        SI Unit of Energy:

        The SI unit of energy is joule and denoted by ‘J’.

        • Larger unit of energy is kilo joule and is denoted by kJ.
        • 1kJ = 1000J
        • Energy required to do 1J of work is 1J of energy.

        Different forms of Energy:

        Things have different forms of energy due to different reasons.

        1. Kinetic Energy
        2. Potential Energy
        3. Chemical Energy
        4. Sound Energy
        5. Light Energy
        6. Heat Energy
        7. Electrical Energy

        Here we will discussed mainly two types of energy: Kinetic Energy and Potential Energy.

        Kinetic Energy:

        • It is the energy possessed by an object due to its motion.
        • Anything moving is said to have kinetic energy.

        For example; here the car is moving so it has kinetic energy.

        http://upload.wikimedia.org/wikipedia/commons/b/bc/DTM_Mercedes_W204_DiResta09_amk.jpg

        Kinetic energy (K.E.) = 1/2mv2

        Here,

        m = Mass of object;

        v = Speed of object;

        • If two objects have same velocity but different masses then object which have more mass possesses more kinetic energy.
        • Similarly more speed means more kinetic energy and vice versa.

         

        Kinetic Energy and Work:

        Consider that initially a body is at rest. If a force is applied on it, body starts moving with some velocity (say v).

        As we applied a force on body, work is done by us and as velocity is changing from zero to ‘v’, there is a change in kinetic energy too.

        Initial K.E. = 0, Final K.E. = 1/2mv2

        So we can say that “if work is done on an object, its kinetic energy changes”.

        Work = Final K.E. – Initial K.E.

        Derivation of formula of K.E :

        Consider a body of mass m moving with velocity v and due to applied force F opposite to direction of velocity, body comes to rest.

        Step 1 – As the ball comes to rest it means force must be applied in a direction opposite to the displacement of ball so,

        W = (-F) x s;

        Step 2 – W = (-ma) x s …(1)

        Step 3 – v2 = u2 + 2as

        Since the body has come to rest so

        0 = v2 – 2as;

        => v2 / 2a

        Step 4 – From equation (1)

        W = (-ma) x v2 / 2a = – 1/2 mv2

        Step 5 – W = Final K.E. – Initial K.E.

        – 1/2 mv2= 0 – initial K.E.

        So, K.E. =  – 1/2 mv2 proved.

        Potential Energy:

        It is the energy possessed by an object due to its position or change in its shape.

        For example:

        • In bow the stretched band can do work as when the stretched band is released the arrow starts moving so we can say that stretched band has energy.

        In this case, energy possessed by the stretched band is due to change in shape.

        • The block on ground can’t do work. The block at high position can do work so it has energy.

        In this case, energy possessed by the block is due to its position.

        On the basis of position and change in shape of object, potential energy is of two type:

        1. Gravitational Potential Energy: It is the energy possessed by a body due to its position above the ground.
        • If an object is at greater height, it has more potential energy.

         

        1. Elastic Potential Energy: It is the energy possessed by a body due to its change in shape.

        Potential Energy (P.E.) = mgh

        Here,

        m = mass of body

        g= 9.8 m/s2

        h= height of object from ground

         

        Mechanical Energy:

        It is defined as the sum of kinetic and potential energy. For example; bird flying in the air has both kinetic and potential energy.

        Mechanical Energy (M.E.) = K.E. + P.E.

        = – 1/2 mv2+ mgh

        Transformation of Energy

        Energy can transform from one form to another. For example; when a body falls from a height to ground potential energy transforms to kinetic energy.

        Energy transformation in gadgets:

        • In fan, electrical energy is transformed into kinetic energy.
        • In bulb, electrical energy is transformed into heat energy then finally into light energy.
        • In riding a bicycle, chemical energy is transformed into muscular then into kinetic energy etc.

        Energy transformation in Nature:

        • During photosynthesis, light energy is transformed into chemical energy;
        • During rain, potential energy is transformed into kinetic energy;
        • During striking of clouds, kinetic energy is transformed into light and sound energy etc.

         

        Law of Conservation of Energy

        Law of conservation of energy says that

        “ Energy can neither be created nor destroyed, but can be converted from one form into another. When energy changes from one form to another, total amount of energy remains constant or conserved ”.

        For example:

        In an iron the electrical energy required to run it is 100J (say), then this energy is converted into heat energy and the energy still remains 100J only its form gets converted not its amount.

        Energy conservation for a falling body:

        • Let’s suppose a ball of mass 1 kg is kept at a distance 4m from ground.

        Potential energy of ball = mgh

        = (1)(10)(4) = 40 J

        • As ball moves down, potential energy decreases. But by conservation of energy, total energy should be constant. It means kinetic energy would increase.
        • Kinetic energy (K.E.) =  1/2 mv2

        Initally velocity is zero, so

        K.E. = 0

        But as ball moves down, velocity is increasing and thus kinetic energy would increase.

        • Thus we can say potential energy is transforming to kinetic energy and total mechanical energy is constant.

        P.E. + K.E. = Mechanical energy = constant

        • When the ball finally hits the ground, it comes to rest and its P.E. and K.E. both are zero.
        • 40 J kinetic energy is converted to sound and heat energy.
        • Sound is produced on hitting and ground gets a bit heated.

        Energy Conservation in Pendulum:

        We know as pendulum oscillates, its height changes.

        • At point A, ball has kinetic energy and no potential energy.
        • When pendulum slowly rise, K.E. decreases and P.E. increases. At point B, ball has potential energy and no kinetic energy.
        • While going from B to A, P.E changes to K.E. At point A, K.E. becomes maximum and P.E energy becomes zero.
        • While going from A to C, K.E changes to P.E. At point C, ball has potential energy and no kinetic energy.
        • While going from C to A, P.E changes to K.E.

        When pendulum stops, both P.E. and K.E. becomes zero and entire energy is converted into sound and heat energy.

        Thus an oscillating pendulum also verifies law of conservation of energy.

        Power

        Power is defined as the rate of doing work. It tells how fast or slow a work is done.

        For example; an aero-plane covers more distance in less time than a car consequently so we say that aero-plane is more powerful than car.

        Power = Work / Time

        => P = W / t

        • SI unit of Power is Joule per second or Js-1.
        • 1 Watt is the power when 1J of work is done in 1s.
        • The bigger unit of power is Kilowatt and represented by kW.

        1kW = 1000 W

        Note – If power is more, work is done fast and vice versa.

        Power can also be defined as the rate of transfer of energy.

        Commercial Unit of Energy

        • Since Joule is very small thus, large quantity of energy is expressed in kilo watt hour and is written as kWh. KWh is the commercial unit of energy.
        • Electric consumption in house is measured in kWh. Therefore, kWh is called commercial unit of energy.

        1 unit = 1 kwh

        • 1 kWh is the energy consumed by a device of power 1kW in 1 hour.

        1 kWh = (1 kW)(1 hr)

        = (1000 W)(60 60s)

        = (1000 J/t) (60 60s) = 3600,000 J

        1 kWh = 3.6 106 J

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