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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 – Gravitation

        Gravitation

        Universal Law of Gravitation

        The Universal law of Gravitation states that any two bodies having mass attract each other with force directly proportional to the product of their mass and inversely proportional to the square of distance between them. The force acts along the line joining the centres of the objects.

        D:\Diagrams\gravitation.jpg

        => F ∝ m1m2 / d2

        => F = Gm1m2 / d2

        Here, G is Universal gravitational constant = 6.673 X 10-11 Nm2kg-2. The value of G was found out by Henry Cavendish.

        Note:

        • If mass of object is large, force will be more. If mass of object is small, force will be less.
        • If distance between two object is more, force exerted will be less and vice versa.

        Importance of Gravitational Force

        • It binds us to Earth.
        • Moon revolves around Earth due to gravitational force. Planets revolve around Sun due to gravitational force.
        • Tides in seas are caused due to gravitational force of moon on earth.

        Free Fall

        The earth attracts objects towards it due to gravitational force. When an object moves such that only gravitational force of earth acts on it, it is said to do “Free Fall”.

        Attraction of Earth on Objects close to its Surface

        When an object is near the surface of earth, the distance between object and centre of the earth will be equal to the radius of earth (i.e.) because the distance of object is negligible in comparison of the radius of earth.

        Therefore,

        F = GMEm / RE2

        F = m (GME / RE2)

        => F = mg …(i)

        Where,

        g = acceleration due to gravity. Value of g = 9.8 m/s2.

         

        Velocity and Acceleration

        • When an object moves with constant velocity, such motion is called uniform motion.
        • When an object moves with increasing velocity, motion is called accelerated motion.
        • When an object moves with decreasing velocity, motion is called retarded motion.

        Direction of velocity is the direction in which body is moving.

        Falling Bodies

        Case 1: When an object is released from top, it falls down due to gravitational force of earth. As force acts downwards, acceleration ‘a’ would be in downward direction.

        As object is moving downwards and acceleration is also in downward direction, velocity increases. So when an object is released from top, it does accelerated motion (increasing velocity).

        Calculation of acceleration ‘a’:

        According to Newton’s 2nd Law

        F = ma

        a = F/m

        From equation (i)

        a = mg/m

        a = g = 9.8 m/s2

        Thus acceleration acted on a falling object is equal to ‘g’ (acceleration due to gravity).

        Case 2: If we throw a ball upward in the air, a gravitational force acts downwards on it. As force acts downwards, acceleration is in downwards direction. It means velocity will decrease with time and at one point, it becomes zero.

        Due to the gravitational force, the ball takes U-turn and reaches to ground with same speed with which it was thrown up. As object is moving downwards and acceleration is also in downward direction, velocity increases.

        D:\Diagrams\RefUpDown.gifNote: We have studied three equations of motion.

        v = u + at

        s = ut + ½at2

        v2 = u2 + 2as

        These equations can be used to calculate the value of velocity, distance, etc by replacing ‘a’ by ‘g’.

        The value of ‘g’ is taken as positive in the case of object moving towards earth and taken as negative in the case of object is thrown in opposite direction of earth.

         

        Air Resistance

        Theoretically, all objects of different shape, size and mass should take same time to fall through same distance. But practically it is observed that two objects of different mass hit the ground at different times due to different air resistance on them.

        Factors affecting Air resistance:

        1. More the mass, lesser the effect of air resistance.
        2. More the surface area of object, more the effect of air resistance.

        Variation in the value of ‘g’

        • As we go at large heights, g decreases.
        • Since, earth is not a perfect sphere rather it has oblique shape. Therefore, radius at the equator is greater than at the poles. Since, value of ‘g’ is reciprocal of the square of radius of earth, thus, the value of ‘g’ will be greater at the poles and less at the equator.
        • Geography of earth is different at different locations such as mountains, plains, oceans. This causes variation in value of g.

        Mass & Weight

        Mass

        Mass is the quantity of matter present. The mass of a body is always constant and does not change from place to place. Mass has no direction and thus it is scalar quanitity. The SI unit of mass is kg. Mass can be measured using beam balanced.

        Weight

        Weight of an object is the gravitational force applied by the earth on that object.

        W = m x g

        The weight of a body changes from place to place, depending on mass of object.

        Since weight always acts vertically downwards, therefore, weight has both magnitude and direction and thus it is a vector quantity. The SI unit of weight is Newton. Weight can be measured using spring balance.

        Weight of an Object on the Surface of Moon

        Mass of an object is same on earth as well as moon. But weight is different.

        Wt. of body on Earth / Wt. of body on Moon = ( GMEm/RE2 ) / ( GMMm/RE2 ) = MERM2 / RE2MM

        = ( 6 x 1024kg ) / ( 6.37 x 106m )2  ( 1.74 x 106m )2 / ( 7.36 x 1022kg )

        => Wt. of body on Earth / Wt. of body on Moon = 6

        => Wt. of body on Earth = 6 (Wt. of body on Moon)

        Or Wt. of body on Moon = 1/6 (Wt. of body on Earth)

        Circular Motion & Gravitational Force

        In circular motion, a force must act on body as its direction of velocity changes. This force is called Centripetal force.

        When moon revolves around earth in circular path, gravitational force of earth provides the centripetal force to moon for circular motion.

        When planets revolve around Sun, gravitational force of Sun provides the centripetal force to planets.

        Thrust and Pressure

        Thrust: Force exerted by an object perpendicular to the surface is called thrust.

        Pressure: Pressure is defined as thrust or force per unit area on a surface.

        Pressure = Thrust / Area

        SI unit of pressure = N/m2 = Nm-2 = Pascal (Pa)

        Since, pressure is indirectly proportional to the surface area of the object, so, pressure increases with decrease in surface area and decreases with increase in surface area.

         

        Pressure in Fluids

        Anything that can flow is called Fluid like liquid and gases.

        Molecules of fluid move around and collide with walls of vessel. Thus fluids apply pressure on walls. Fluids exert pressure in all directions.

        Buoyancy & Buoyant Force: Fluid applies an upward force on a solid which is partially or fully submerged in liquid. This phenomenon is called buoyancy (Upthrust) and applied upward force is called buoyant force.

        Experiment – 1:

        Take a empty bottle and float it on water. If we push it down in the water partially or fully and then release, bottle suddenly jumps upward. This is because the water applies an upward force on bottle.

        Experiment – 2:

        Hang a rubber string. Attach a stone to the rubber string. String will elongate. Submerge the stone in water – filled bucket. The elongation in string decreases.

        This happens due to upward buoyant force of water.

        Archimedes Principle

        When an object is fully or partially submerged in a liquid, buoyant force acts on it in upward direction. Its value is equal to weight of liquid displaced.

        For example, suppose an object is partially submerged in a liquid and the mass of displaced liquid is 1.5 kg. Then

        Buoyant force applied on the object (F) = Weight of liquid displaced = mg

        = (1.5)(9.8) = 14.7 N

        Archimedes principle has many uses. It is used in designing ships, submarines, air balloons etc.

        Density 
        The density of a substance is the mass of a unit volume of the substance.

        Density = Mass / Volume

        Every material has its own density. The SI unit of density is kilogram per metre cube (kg m -3).

        Material Density (kg / m3)
        Aluminum 2,700
        Blood 1,600
        Brass 8,600
        Copper 8,900
        Gold 19,300
        Iron 7,800
        Lead 11,300
        Mercury 13,600
        Platinum 21,400
        Silver 10,500
        Steel 7,800
        Water 1,000

        Relative Density
        The relative density of a substance is the ratio of the density of a substance to the density of water.

        Relative Density = Density of a substance / Density of water

        Since relative density is a ratio of similar quantities, it has no unit.

        Prev Archimedes Principle; Density
        Next NCERT Solutions – Gravitation

          1 Comment

        1. Rajat sharma
          January 26, 2022
          Reply

          Thanks

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