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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 – Force and Newtons Laws of Motion

        Force and Newton’s Laws of Motion

        A push or pull on a body is called force. Forces are used in our everyday actions like pushing, lifting, pulling, stretching, twisting and pressing. A force cannot be seen. A force can be judged only by the effects which it can produce in several bodies (or objects) around us.

        push20and20pullForce has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of Newton and represented by the symbol F.

        In the below shown images we can see how forces are being applied in our everyday life:

        Effects of Force

        • Force can make a stationary body in motion. For example a football can be set to move by kicking it, i.e. by applying a force.
        • Force can stop a moving body – For example by applying brakes, a running cycle or a running vehicle can be stopped.
        • Force can change the direction of a moving object. For example; by applying force, i.e. by moving handle the direction of a running bicycle can be changed. Similarly by moving steering the direction of a running vehicle is changed.
        • Force can change the speed of a moving body – By accelerating, the speed of a running vehicle can be increased or by applying brakes the speed of a running vehicle can be decreased.
        • Force can change the shape and size of an object. For example; by hammering, a block of metal can be turned into a thin sheet. By hammering a stone can be broken into pieces.

        Balanced and Unbalanced Forces

        1. Balanced Forces

        If the resultant of applied forces is equal to zero, it is called balanced forces. Balanced forces do not cause any change of state of an object. Balanced forces are equal in magnitude and opposite in direction. Balanced forces can change the shape and size of an object. For example – When forces are applied from both sides over a balloon, the size and shape of balloon is changed.

        1. Unbalanced Forces

        If the resultant of applied forces are greater than zero the forces are called unbalanced forces. An object in rest can be moved because of applying balanced forces.

        Unbalanced forces can do the following:

        1. Move a stationary object.
        2. Increase the speed of a moving object.
        3. Decrease the speed of a moving object.
        4. Stop a moving object.
        5. Change the shape and size of an object.

        Some Common Forces

        1. Muscular Force: The force obtained by the working of human body muscles is called muscular force. Ex: Lifting objects, doing exercise etc.
        2. Gravitational Force: The force applied by earth on an object in downward direction is called gravitational force.
        3. Frictional Force: The force which opposes motion is known as frictional force. It acts in the direction opposite to the velocity of body.
        4. Air Resistance: When an object moves through air, air applies a small force in direction opposite to velocity. This force is called air resistance.

        Newton’s Laws of Motion

        Newton has given three laws to define the motion of bodies. These laws are known as Newton’s laws of motion.

        Newton’s 1st Law

        A body at rest will remain in rest, and a body in motion will continue in motion in a straight line with uniform speed, unless it is compelled by an external force to change its state of rest or of uniform motion.

        C:\Users\Sony\AppData\Local\Microsoft\Windows\INetCache\Content.Word\force-and-laws-of-motion-8-728.jpgInertia and Mass: Inertia is that property of body due to which it resists a change in its state of rest or of uniform motion.

        In this above shown picture the inertia of the coin tries to maintain its state of rest even when the card flows off. The mass of an object is a measure of its inertia. Its SI unit is kilogram (kg).

        Application of Newton’s 1st Law

        1. A passenger in bus has a tendency to keep moving in a straight line inside a bus due to inertia. When the bus takes turn, body of passenger wants to continue moving in straight line. Due to this, it appears that his body bends outwards.
        2. When we hit a carpet it loses inertia of rest and moves. But the dust in it retains inertia of rest and is left behind. Thus dust and carpet are separated.
        3. When a tree is shaken, it moves to and fro. But fruit remains at rest due to its inertia of rest. Due to this fruit breaks off the tree.
          C:\Users\Sony\Desktop\Work\bwpRZ99bGG-4.png
        4. When a car is braked suddenly, the man bends forward violently due to inertia of motion. The man may collide with parts of car hurting himself. Seatbelt will not let the man bend forward. And thus save them from accident.
          C:\Users\Sony\Desktop\Work\PG11C11_017.png
        5. Due to inertia of motion even when the car stops, the luggage on the top of car has the tendency to move forward. Therefore luggage is tied.
          C:\Users\Sony\Desktop\Work\Car-top-luggage-carrier-Subaru-Forester-JW-8-5-12.JPG

        Momentum: The momentum of a body is defined as the product of its mass and velocity.

        Thus, momentum = mass x velocity

        Or, p = m x v

        Where, p = momentum

        m = mass of the body

        v = velocity of the body

        The SI unit of momentum is kilograms meters per second (kg.m/s)

        Note: The force required to stop a moving body is directly proportional to its mass and velocity.

         

        Change in momentum: It is defined as the difference between final momentum and initial momentum. Suppose initial momentum is mu, and final momentum is mv, then

        Change in momentum = mv – mu

        Rate of change of momentum: The rate at which momentum is changing is known as rate of change of momentum.

        Rate of change of momentum =mv – mu / t

        Or, = m (v-u) / t

        Newton’s 2nd Law

        The rate of change of momentum of a body is directly proportional to the applied force, and takes place in the direction in which the force acts.

        Force = change in momentum / time taken

        F = mv – mu / t

        = But we know that

        F = m x a

        Or Force = Mass x Acceleration

        Its SI unit is Newton (N).

        Thus, one unit of force is defined as the amount that produces an acceleration of 1 m s-2 in an object of mass 1 kg.

        Application of Newton’s 2nd Law:

        1. When we stop the ball gradually, we need to apply less force. This is easy and safe. If we stop the ball suddenly, we need to apply larger force which is difficult and can also injure our hand.
        2. In high jump if surface is hard, athlete’s body changes velocity in very less time. Large force acts on his body due to which he may get injured. If the surfaces are soft, athlete’s body changes velocity in more time. And less force acts on his body which is safe.
          C:\Users\Sony\Desktop\Work\0.jpg

        Newton’s 3rd Law

        Whenever one body exerts a force on another body, the second body exerts an equal and opposite force to the first body. Or, to every action there is an equal and opposite reaction.

        Action and reaction forces are equal and opposite.

        Application of Newton’s 3rd Law:

        1. Gun applies force on bullet due to which it moves ahead. By Newton’s 3rd Law, bullet will also apply same force on gun in backward direction. Due to this force, gun moves back. This is called recoil of gun. Gun moves back only by small amount due to its heavy mass.
        2. Hose pipe applies large force on water due to which water moves ahead. By Newton’s 3rd Law water applies the same force on pipe backwards. Due to this force, pipe can move backwards. To stop it, many people need to hold it.
        3. Man pushes the boat backwards and by newton’s 3rd law, boat pushes man forward.
        4. Man pushes water back by applying force. By Newton’s 3rd Law, water applied equal and opposite force on swimmer. Due to this force man moves ahead.

         

        1. Cheetah applies forces on ground in backward direction. By 3rd law, ground applies force equal and opposite on cheetah in forward direction. It is due to this force that cheetah moves ahead. For running faster cheetah needs to apply more force on ground in forward direction.

        Conservation of Momentum

        If two or more objects apply force on each other with no external force, their final momentum remains same as initial momentum.

        Total momentum before collision = Total momentum after collision

        Practical examples of conservation of momentum:

        1. In rocket, fuel is burnt due to which gases are ejected downwards. For conservation of momentum, rocket moves up.
        2. Fuel in jet plane burns and ejects gases in backward direction. Then by conservation of momentum, plane moves ahead.
        Prev Practical Applications of Conservation of Momentum
        Next NCERT Solutions – Force and Newtons Laws of Motion

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