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      Class 11 PHYSICS – JEE

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      • Class 11
      • Class 11 PHYSICS – JEE
      CoursesClass 11PhysicsClass 11 PHYSICS – JEE
      • 1.Basic Maths (1) : Vectors
        7
        • Lecture1.1
          Vector and Scalar, Representation of Vectors, Need for Co-ordinate System, Distance & Displacement 39 min
        • Lecture1.2
          Mathematics of Vectors, Triangle Law and Parallelogram Law 01 hour
        • Lecture1.3
          Addition More than Two Vectors, Subtraction of Vectors- Displacement vector 28 min
        • Lecture1.4
          Elementary Maths 14 min
        • Lecture1.5
          Unit Vectors, Special Unit Vectors, Resolution of Vectors 49 min
        • Lecture1.6
          Addition & Subtract using Unit Vectors, 3 D Vectors, Product of Vectors 54 min
        • Lecture1.7
          Chapter Notes – Basic Maths (1) : Vectors
      • 2.Basic Maths (2) : Calculus
        4
        • Lecture2.1
          Delta, Concept of Infinity, Time Instant Interval, Rate of Change, Position and Velocity 40 min
        • Lecture2.2
          Fundamental Idea of Differentiation- Constant Multiplication Rule, Sum/Difference Rule 29 min
        • Lecture2.3
          Trigonometric functions, Log function, Product Rule, Quotient Rule, Chain Rule 25 min
        • Lecture2.4
          Integration- Formulas of Integration, Use of Integration 45 min
      • 3.Unit and Measurement
        13
        • Lecture3.1
          Unit, History of Unit of Length-Metre, Properties of a Good Unit 21 min
        • Lecture3.2
          Concept of Derived Units, Fundamental Physics Quantities and Prefix of Units 38 min
        • Lecture3.3
          Unit-less Derived Quantities, Supplementary Quantities, Systems of Unit, Unit Conversion 39 min
        • Lecture3.4
          Dimensional Analysis, Dimension and Unit, Dimensionless Quantities 32 min
        • Lecture3.5
          Principle of Homogeneity 34 min
        • Lecture3.6
          Dimensionally Correct/Incorrect Equations, Use of Dimensional Analysis 41 min
        • Lecture3.7
          More Units of Length and Measurement of Length 47 min
        • Lecture3.8
          Errors and Their Reasons 36 min
        • Lecture3.9
          Combination of Errors 42 min
        • Lecture3.10
          Round Off, Significant Figures, Exponent Form of Numbers/Scientific Notation 27 min
        • Lecture3.11
          Chapter Notes – Unit and Measurement
        • Lecture3.12
          NCERT Solutions – Unit and Measurement
        • Lecture3.13
          Revision Notes – Unit and Measurement
      • 4.Motion (1) : Straight Line Motion
        10
        • Lecture4.1
          Meaning of Dimension; Position; Distance & Displacement 25 min
        • Lecture4.2
          Average Speed & Velocity; Instantaneous Speed & Velocity 31 min
        • Lecture4.3
          Photo Diagram; Acceleration- Direction of acceleration, Conceptual Examples 22 min
        • Lecture4.4
          Constant Acceleration; Equations of constant acceleration 43 min
        • Lecture4.5
          Average Velocity Examples and Concepts; Reaction Time 19 min
        • Lecture4.6
          Free Fall under Gravity 30 min
        • Lecture4.7
          Variable Acceleration; Derivation of Constant Acceleration Equations 48 min
        • Lecture4.8
          Chapter Notes – Motion (1) : Straight Line Motion
        • Lecture4.9
          NCERT Solutions – Straight Line Motion
        • Lecture4.10
          Revision Notes Straight Line Motion
      • 5.Motion (2) : Graphs
        3
        • Lecture5.1
          Tangent & Chord; Slope of Line- Chord & Tangent; Meaning of x/t graph, v/t graph, a/t graph 59 min
        • Lecture5.2
          Graph Conversion 51 min
        • Lecture5.3
          Area Under Curve 22 min
      • 6.Motion (3) : Two Dimensional Motion
        6
        • Lecture6.1
          Projectile on Level Ground 32 min
        • Lecture6.2
          Terms Related to Projectile on Level Ground 31 min
        • Lecture6.3
          Not Level to Level Projectile, Problem Solving, Dot Product 34 min
        • Lecture6.4
          Equation of Trajectory and Some Miscellaneous Questions 35 min
        • Lecture6.5
          Projectile on Inclined Plane 39 min
        • Lecture6.6
          Collision of Projectile and Avg. Acceleration in 2D Motion 16 min
      • 7.Motion (4) : Relative Motion
        7
        • Lecture7.1
          Reference Frame and Distance of Closest Approach 45 min
        • Lecture7.2
          Relative Motion in 2D 26 min
        • Lecture7.3
          Free Fall & Relative Motion 26 min
        • Lecture7.4
          Throwing Object from Moving Body 32 min
        • Lecture7.5
          Rain Problem (theory)- and Wind in Rain Problem 32 min
        • Lecture7.6
          River Based Problem 26 min
        • Lecture7.7
          Crossing River by Shortest Distance- Least Time to Cross River; Wind Problems; Relative Approach 27 min
      • 8.Newton's Laws of Motion
        8
        • Lecture8.1
          Force and Newton’s Laws 33 min
        • Lecture8.2
          Normal Reaction, Free Body Diagram(F.B.D), Normal on circular bodies, Mass and Weight 57 min
        • Lecture8.3
          Tension Force(Ideal Pulley, Clamp Force), Internal & External Force, Heavy Rope 01 hour
        • Lecture8.4
          Spring Force(Sudden Change, Series and Parallel Cutting of Spring) 01 hour
        • Lecture8.5
          Inertia and Non-Inertial Frames(Pseudo Force), Action-Reactin Pair, Monkey Problem 49 min
        • Lecture8.6
          Chapter Notes – Newton’s Laws of Motion
        • Lecture8.7
          NCERT Solutions – Laws of Motion
        • Lecture8.8
          Revision Notes Laws of Motion
      • 9.Constrain Motion
        3
        • Lecture9.1
          Force of mass-less body; Constrain Motion- Pulley Constrain 1 01 hour
        • Lecture9.2
          Pulley constrain 2, Alternate Method; Wedge Constrain- Proof 49 min
        • Lecture9.3
          Relative Constrain 01 hour
      • 10.Friction
        6
        • Lecture10.1
          Kinetic friction Theory- Theory, Angle of friction 32 min
        • Lecture10.2
          Static Friction Theory- Based on Example 2, Direction of friction Theory 01 min
        • Lecture10.3
          Some Advanced Examples 18 min
        • Lecture10.4
          Block Over Block Theory 01 hour
        • Lecture10.5
          Conveyor belt, Static and kinetic co-eff. of friction, Friction on wheels, Theoretical examples 27 min
        • Lecture10.6
          Chapter Notes – Friction
      • 11.Circular Motion
        6
        • Lecture11.1
          Ex. on Average Acc. and Angular Variables Theory and Ref. Frame 52 min
        • Lecture11.2
          Uniform Circular Motion and Centripetal Force 40 min
        • Lecture11.3
          Non-Uniform Center of Mass – Theory by Ex 2; Friction 01 hour
        • Lecture11.4
          Centrifugal Force and Banking of Roads 01 hour
        • Lecture11.5
          Radius of Curvature- Radius of Curvature; Axial Vector; Well of Death 34 min
        • Lecture11.6
          Chapter Notes – Circular Motion
      • 12.Work Energy Power
        15
        • Lecture12.1
          Work & its calculation and Work-done on curved path 31 min
        • Lecture12.2
          Work-done by Different Forces 01 hour
        • Lecture12.3
          Work Energy Theorem and W.E. th in Non-inertial frame, W.E. th and Time 23 min
        • Lecture12.4
          Work Energy Theorem for System 55 min
        • Lecture12.5
          Energy and Different Forms of Energy-and Energy of Chain; Potential Energy & Reference Frame 28 min
        • Lecture12.6
          Potential Energy Curve and Power 01 hour
        • Lecture12.7
          Normal Reaction, Vertical Circular Motion, Motion in Co-Concentric Spheres 27 min
        • Lecture12.8
          Motion on Outer Surface of Sphere, Motion on Inner Surface of Fixed Sphere 59 min
        • Lecture12.9
          Motion on Rope, Motion on Rod 32 min
        • Lecture12.10
          VCM – 1 31 min
        • Lecture12.11
          VCM – 2 01 hour
        • Lecture12.12
          VCM – 3 22 min
        • Lecture12.13
          Chapter Notes – Work Energy Power
        • Lecture12.14
          NCERT Solutions – Work Energy Power
        • Lecture12.15
          Revision Notes Work Energy Power
      • 13.Momentum
        9
        • Lecture13.1
          Introduction and Conservation of Momentum 35 min
        • Lecture13.2
          Impulsive Force – Characteristics of Impulsive Force 30 min
        • Lecture13.3
          Momentum Conservation in Presence of External Force – Two Steps Problems 41 min
        • Lecture13.4
          Questions Involving Momentum & Work Energy Theorem 27 min
        • Lecture13.5
          Collision – Head – on Collision and Special Cases of Head – on Collision 39 min
        • Lecture13.6
          Oblique Collision 24 min
        • Lecture13.7
          Collision of Ball with Flat Surface 38 min
        • Lecture13.8
          Impulse and Average Force 58 min
        • Lecture13.9
          Advanced Questions 50 min
      • 14.Center of Mass
        5
        • Lecture14.1
          Center of Mass (CM) Frame and Kinetic Energy in C – Frame 29 min
        • Lecture14.2
          Finding Center of Mass by Replacement Method and Finding CM of Plate with Hole 36 min
        • Lecture14.3
          Finding CM by Integration and CM of Some Standard Objects 57 min
        • Lecture14.4
          Motion of CM; Newton’s 2nd Law for CM; CM in Circular Motion 41 min
        • Lecture14.5
          Revision Notes Center of Mass
      • 15.Rotational Motion
        14
        • Lecture15.1
          Rigid Body – Motion of Rigid Body; Axis of Rotation 14 min
        • Lecture15.2
          Vector Product/ Cross Product; Torque 44 min
        • Lecture15.3
          Couple and Principle of Moments 48 min
        • Lecture15.4
          Pseudo Force and Toppling – Overturning of Car 01 hour
        • Lecture15.5
          Moment of Inertia 01 hour
        • Lecture15.6
          Parallel Axis Theorem; Perpendicular Axis Theorem; Quantitative Analysis; Radius of Gyra 01 hour
        • Lecture15.7
          Analogy b/w Transnational & Rotational Motion; Relation b/w Linear and Angular Velocity; Dynamics of Rotation 40 min
        • Lecture15.8
          Angular Momentum 30 min
        • Lecture15.9
          Angular Momentum of a Particle 32 min
        • Lecture15.10
          Rotational Collision 49 min
        • Lecture15.11
          Kinetic Energy, Work, Power; Potential Energy; Linear & Angular Acceleration; Hinge Force; Angular Impulse 02 hour
        • Lecture15.12
          Chapter Notes – Rotational Motion and Rolling Motion
        • Lecture15.13
          NCERT Solutions – Rotational Motion
        • Lecture15.14
          Revision Notes Rotational Motion
      • 16.Rolling Motion
        11
        • Lecture16.1
          Introduction to Rolling Motion 40 min
        • Lecture16.2
          Rolling Motion on Spool 24 min
        • Lecture16.3
          Friction 59 min
        • Lecture16.4
          Direction of Friction 01 hour
        • Lecture16.5
          Rolling on Moving Platform and Motion of Touching Spheres 44 min
        • Lecture16.6
          Rope Based Questions 55 min
        • Lecture16.7
          Work-done by Friction in Rolling Motion, Kinetic Energy in Transnational + Rotational Motion 29 min
        • Lecture16.8
          Angular Momentum in Rotation + Translation 01 hour
        • Lecture16.9
          Angular Collision 01 hour
        • Lecture16.10
          Instantaneous Axis of Rotation 50 min
        • Lecture16.11
          De-Lambart’s Theorem 50 min
      • 17.Gravitation
        8
        • Lecture17.1
          Gravitation force, Universal Law of Gravitation, Gravitational Force due to Hollow Sphere and Solid Sphere 35 min
        • Lecture17.2
          Acceleration due to Gravity and Rotation of Earth 42 min
        • Lecture17.3
          Potential Energy, Questions and Solutions 56 min
        • Lecture17.4
          Satellites, Circular Motion, Geostationary Satellites and Polar Satellites 42 min
        • Lecture17.5
          Polar Satellites, Weightlessness in Satellites, Trajectories and Kepler’s Laws 29 min
        • Lecture17.6
          Chapter Notes – Gravitation
        • Lecture17.7
          NCERT Solutions – Gravitation
        • Lecture17.8
          Revision Notes Gravitation
      • 18.Simple Harmonic Motion
        13
        • Lecture18.1
          Oscillatory Motion – Horizontal Spring Block System, Qualitative Analysis of Horizontal Spring System 33 min
        • Lecture18.2
          Quantitative Analysis of Horizontal Spring System; Frequency and Angular Frequency; Velocity and Acceleration; Mechanical Energy 47 min
        • Lecture18.3
          Relating Uniform Circular Motion and SHM and Phasor Diagram 30 min
        • Lecture18.4
          Equation of SHM and Problem Solving using Phasor Diagram 39 min
        • Lecture18.5
          Questions 40 min
        • Lecture18.6
          More Oscillating Systems – Vertical Spring Block System 41 min
        • Lecture18.7
          Angular Oscillations – Simple Pendulum 34 min
        • Lecture18.8
          Compound / Physical Pendulum, Torsional Pendulum, Equilibrium of Angular SHM; Differentiation by Chain Rule 38 min
        • Lecture18.9
          Energy Method to find Time Period 30 min
        • Lecture18.10
          Finding Amplitude of SHM 30 min
        • Lecture18.11
          Block Over Block and Elastic Rope 33 min
        • Lecture18.12
          Superposition of Horizontal SHMs and Perpendicular 30 min
        • Lecture18.13
          Damped Oscillations 28 min
      • 19.Waves (Part-1)
        11
        • Lecture19.1
          Wave, Plotting and Shifting of Curves, Meaning of y/t and y/x Graph, Wave is an Illusion!, 1D Wave on String 55 min
        • Lecture19.2
          Wave Equation, Analysis of Wave Equation and Wave Velocity 55 min
        • Lecture19.3
          Sinusoidal Wave (Harmonic Wave), Wave Equation for Sinusoidal Wave, Particle Velocity, Slope of Rope, Wave Velocity 01 hour
        • Lecture19.4
          Superposition of Waves 44 min
        • Lecture19.5
          Reflection of Waves 37 min
        • Lecture19.6
          Standing Waves 01 hour
        • Lecture19.7
          Tuning Fork, Sonometer and Equation of Standing Waves 54 min
        • Lecture19.8
          Energy in Waves 54 min
        • Lecture19.9
          Chapter Notes – Waves
        • Lecture19.10
          NCERT Solutions – Waves
        • Lecture19.11
          Revision Notes Waves
      • 20.Waves (Part-2)
        10
        • Lecture20.1
          Waves, Propagation of Sound Wave and Wave Equation 27 min
        • Lecture20.2
          Sound as a Pressure Wave 38 min
        • Lecture20.3
          Speed of Sound, Laplace Correction and Intensity of Sound Waves 59 min
        • Lecture20.4
          Spherical and Cylindrical Sound Waves 31 min
        • Lecture20.5
          Addition of Sin Functions, Interference of Sound Waves of Same Frequency, Interference of Coherent Sources 01 hour
        • Lecture20.6
          Quinke’s Apparatus 32 min
        • Lecture20.7
          Interference of Sound Waves of Slightly Different Frequencies (Beats) 39 min
        • Lecture20.8
          Reflection of Sound Waves, Standing Waves, End Correction 39 min
        • Lecture20.9
          Standing Waves in Terms of Pressure, Standing Waves on Rods, Kund’s Tube, Resonance Tube Experiment 49 min
        • Lecture20.10
          Doppler Effect, Reflection from Wall, Doppler Effect in 2 Dimension 01 hour
      • 21.Mechanical Properties of Solids
        6
        • Lecture21.1
          Rigid body,Strain, Stress,Hook’s Law 25 min
        • Lecture21.2
          Breaking Stress 26 min
        • Lecture21.3
          Shear Stress and Strain, Bulk Modulus, Elasticity and Plasticity, Stress-Strain Curve, Young’s Modulus 34 min
        • Lecture21.4
          Chapter Notes – Mechanical Properties of Solids
        • Lecture21.5
          NCERT Solutions – Mechanical Properties of Solids
        • Lecture21.6
          Revision Notes Mechanical Properties of Solids
      • 22.Thermal Expansion
        5
        • Lecture22.1
          Linear Expansion; Second’s Pendulum; Bimetallic Strip; Expansion of Hole; Thermal Stress 01 hour
        • Lecture22.2
          Areal/Superficial Expansion; Volume Expansion; Thermal Expansion of Liquid; Measurement of Temperature; Anomal 01 hour
        • Lecture22.3
          Arial/Superficial Expansion; Volume Expansion; Thermal Expansion of Liquid; Measurement of Temperature 38 min
        • Lecture22.4
          Chapter Notes – Thermal Expansion
        • Lecture22.5
          NCERT Solutions – Thermal Expansion
      • 23.Heat and Calorimetry
        2
        • Lecture23.1
          Internal Energy; Heat Energy; Thermal Equilibrium; Zeroth Law of Thermodynamics; Specific Heat Capacity; Latent Heat 48 min
        • Lecture23.2
          Mixing of Substances; Water Equivalent; Units; Calorimeter; Melting Point and Boiling Point; Sublimation 01 hour
      • 24.Heat Transfer
        6
        • Lecture24.1
          Conduction; Comparison between Charge Flow & Heat Flow 42 min
        • Lecture24.2
          Equivalent Thermal Conductivity; Heat Transfer and Calorimetry; Use of Integration; Length Variation 44 min
        • Lecture24.3
          Convection; Radiation, Black Body, Prevost Theory, Emissive Power & Emissivity, Kirchoff’s Law, Stefan – Boltzman Law 01 hour
        • Lecture24.4
          Newton’s Law of Cooling, Cooling Curve; Wien’s Displacement Law; Thermo Flask 48 min
        • Lecture24.5
          Chapter Notes – Heat Transfer
        • Lecture24.6
          Revision Notes Heat Transfer
      • 25.Kinetic Theory of Gases
        6
        • Lecture25.1
          Model of Gas,Postulates of Kinetic Theory of Gases, Ideal Gas, Mean free Path, Maxwell’s speed Distribution 37 min
        • Lecture25.2
          Volume, Pressure of Gases, Kinetic Energy, Temperature, Ideal Gas Equation 45 min
        • Lecture25.3
          Gas Laws, Internal energy of Gas, Degree of Freedom, Degree of Freedom of Mono-atomic and Diatomic Gas 56 min
        • Lecture25.4
          Chapter Notes – Kinetic Theory of Gases
        • Lecture25.5
          NCERT Solutions – Kinetic Theory of Gases
        • Lecture25.6
          Revision Notes Kinetic Theory of Gases
      • 26.Thermodynamics
        9
        • Lecture26.1
          State Equation; Thermodynamic Process; Process Equation & Graph; Work done by Gas 01 hour
        • Lecture26.2
          Heat – Work Equivalence; 1st Law of Thermodynamics; Adiabatic Process 57 min
        • Lecture26.3
          Workdone in Adiabatic Process; Specific Molar Heat Capacity 39 min
        • Lecture26.4
          Poly-tropic Process, Bulk Modulus; Free Expansion; Mixture of Gases 54 min
        • Lecture26.5
          Heat Engine, Refrigerator or Heat Pump, Energy Conservation, Kelvin-Plank Statement, Clausius Statement 01 hour
        • Lecture26.6
          Carnot Cycle, Reversible and Irreversible Process, Specific Heat Capacity of Solids and Water 01 hour
        • Lecture26.7
          Chapter Notes – Thermodynamics
        • Lecture26.8
          NCERT Solutions – Thermodynamics
        • Lecture26.9
          Revision Notes Thermodynamics
      • 27.Fluids
        14
        • Lecture27.1
          Introduction, Pressure of Liquid 47 min
        • Lecture27.2
          Manometer, Barometer 41 min
        • Lecture27.3
          Pascal Law, Hydraulic Lift 35 min
        • Lecture27.4
          Accelerated Liquid, Vertical and Horizontal Acceleration, Pressure Variation in Horizontally Accelerated Liquid 57 min
        • Lecture27.5
          Rotating Liquid, Rotating Liquid in U-Tube 28 min
        • Lecture27.6
          Archimedes’ Principle, Hollow Objects 59 min
        • Lecture27.7
          Apparent Weight, Variation of Liquid Force with Height 01 hour
        • Lecture27.8
          Multiple Liquids 34 min
        • Lecture27.9
          Center of Bouyancy 28 min
        • Lecture27.10
          Fluid Dynamics, Equation of Continuity 48 min
        • Lecture27.11
          Magnus Effect 37 min
        • Lecture27.12
          Venturimeter, Pitot Tube 27 min
        • Lecture27.13
          Questions and Solutions 31 min
        • Lecture27.14
          Chapter Notes – Fluids
      • 28.Surface Tension and Viscosity
        6
        • Lecture28.1
          Surface Tension, Surface Energy 52 min
        • Lecture28.2
          Force of Cohesion, Force of Adhesion, Angle of Contact, Radius of Meniscus, Capillary Rise 54 min
        • Lecture28.3
          Pressure Difference Across Meniscus, Variation of Surface tension with Temperature 27 min
        • Lecture28.4
          Viscous Force 35 min
        • Lecture28.5
          Terminal Velocity, Velocity Gradient, Renolds Number, Turbulent Flow, Streamline Flow 41 min
        • Lecture28.6
          Chapter Notes – Surface Tension and Viscosity

        Chapter Notes – Newton’s Laws of Motion

        FORCE

        We know by experience that all bodies in nature interact in some way with one another. Force is a measure of the interaction of bodies or of the particles of which the bodies consist. The force may produce either deformation (change in the size or shape of bodies) or acceleration (change in magnitude or direction of velocity).

        Force is a vector quantity. Every force has a definite direction and the result of its action depends on the direction and the magnitude of the force.

        If several forces are applied to a particle, they can be replaced by a resultant force. This resultant is the vector sum of the forces and can be found by any of the methods illustrated earlier.

        SOME COMMON FORCES 

        There are basically five forces which we commonly encounter in mechanics problems, namely Weight, Normal Force, Friction Force, Tension and Spring Force.

        Weight
        The weight W⃗  of a body is a force that pulls the body directly towards the earth. The force is due to gravitational attraction between two bodies. We will discuss this in detail later. Here, we consider an object of mass m located at a point where the free fall acceleration has magnitude g. Then the magnitude W of the weight is

        W=mg

        Its direction being vertically downward (towards the centre of the earth).
        Normally we assume that weight is measured in an inertial frame. If it is measured in a non-inertial frame, it is called apparent weight.

        Contact Forces
        Whenever two surfaces are in contact they exert forces on each other. Such forces are known as contact forces. It is convenient to resolve these contact forces into components, one parallel to the contact surface, the other perpendicular to that surface.

        Normal Force
        The normal force is the component of the contact force that is perpendicular to the surface. It is a measure of how strongly the surfaces in contact  are pressed together. As an example push your hand straight down on the table. The force you feel resisting your push is the normal force of the table pushing up on your hand.

        Frictional Force
        The component of the contact force parallel to the contact surface is called frictional force. The direction of the frictional force is opposite to the relative motion (or attempted motion) of the two surfaces in contact.

        Tension
        The force exerted at any point in the rope/string/wire/rod is called the tension at that point. We may measure the tension at any point in the rope by cutting a suitable length from it and inserting a spring scale; the tension is the reading of the scale. The tension is same at all points in the rope only if the rope is unaccelerated and assumed to be massless.

        Spring Force
        As you may have discovered for yourself, springs resists attempts to change their length. In fact, the more you alter a spring’s length, the harder it resists. The force exerted by a spring may be represented as:

        F=−kx

        where x is the change in length, and k is the stiffness constant or simply, the spring constant. Unit of spring constant is N/m. This equation is also known as Hooke’s law. The minus sign in Hooke’s law shows that the direction of the force exerted by the spring is opposite to the displacement that produces it.
        The spring constant depends on geometry of the spring and on the material property. For us, it is important to know that the spring constant is inversely proportional to its length, other things remaining the same. i.e.

        k∝1l   (everything else constant)

        Therefore if you cut a spring into two parts whose length are in ratio 1 : 2, their spring constants will be in ratio of 2 : 1. As in case of rope, we will usually deal with a massless spring, the force at each point of which is the same. Such spring and ropes are normally referred to as ideal.

        NEWTON’S LAWS

        Newton’s First Law

        When there is no net force on an object
        – an object at rest remains at rest, and
        – an object in motion continues to move with a velocity that is constant in magnitude and direction.

        Note
        1) Newton’s first law really describes a reference frame. The property of the body to remain at rest or to retain its uniform linear motion in the absence of applied force is called inertia.
        The first law is often called the law of inertia and the reference frames to which it applies are termed as inertial reference frames.
        Thus an inertial reference frame is one which is either at rest or moves with a constant velocity relative to earth. Truly speaking, the earth itself is not an inertial reference frame (because it rotates as well as moves round the sun in an orbit) but for most practical purposes we can treat it as an inertial reference frame.

        2) This law does not differentiate between objects at rest and objects moving with constant velocity. Indeed, an object moving with constant velocity in one inertial reference frame can be at rest in another inertial reference frame.

        3) No net force here may mean the absence of all forces or the presence of forces whose resultant is zero.

        Newton’s Second Law

        We know from the first law, what happens when there is no unbalanced force on an object: its velocity remains constant. Now let us see What happens when there is an unbalance force on an object ? The Newton’s second Law gives answer to this question, that is, net force acting on a body will produce an acceleration.
        When there is a constant unbalanced force on an object, the object moves with constant acceleration. Furthermore, if the force varies, the acceleration varies in direct proportion with larger force producing larger acceleration. Twice the force produces twice the acceleration in the same mass.

        The magnitude of the acceleration produced depends on the quantity of matter being pushed. The quantity of matter is referred to as the inertial mass.
        Newton’s second law states the relation between the net force and the inertial mass.

        ∑F⃗ =ma⃗ 

        Note that the direction of acceleration is in the direction of the net force.
        In terms of components
        ∑Fx=max      ∑Fy=may      ∑Fz=maz

        Newton’s Third Law

        Experiments show that forces occur in pairs. If you push against a wall, the wall pushes back at you. If one body A applies a force F⃗ BA on another body B, body B applies an equal but oppositely directed force F⃗ AB on  A i.e.

        F⃗ BA=−F⃗ AB

        Normally, one of these force (it does not matter which) is called the action force and the other is called the reaction force.  Thus the third law is also sometimes stated as “To every action there is always an equal and opposite reaction”. Note that the action and reaction always act on different objects.

        FREE BODY DIAGRAM

        In the application of any of the Newton’s laws, it is absolutely necessary to account correctly for all forces acting on the particle. The only forces that we may neglect are those whose magnitudes are negligible compared with other forces acting, such as the force of mutual attraction between two particles compared with their attraction to a body having large mass such as the earth. The only reliable way to account accurately and consistently for every force is to isolate the particle under consideration from all contacting and influencing bodies and replace the bodies removed by the forces they  exert on the particle isolated. The resulting free-body diagram (F.B.D.) is the  means by which every force, known and unknown, that acts on the particle is represented and hence account for. Only after this vital step has been completed should the appropriate equation or equations of motion be written.

        As a part of the drawing of a free-body diagram, the coordinates axes and their positive directions should be clearly indicated. Also, the acceleration components are indicated by the side of the free-body diagram.

        EQUILIBRIUM OF BODIES

        A body or a system is said to be in equilibrium if it does not tend to undergo any further change of its own. Any further change must be produced by external means (e.g. force).
        A body is said to be in translational equilibrium if the sum of the forces acting on the body is zero.

        ∑F⃗ net=0

        If the particle is at rest, it is in static equilibrium. If it is moving at constant velocity, it is in dynamic equilibrium.  In either case ∑F⃗ =0. In terms of components ∑Fx=0, ∑Fy=0 and ∑Fz=0.
        The simplest kind of equilibrium situation is one where two forces act on a body. When you stand motionless, you experience the downward gravitational pull of the earth, your weight W⃗ . The weight is balanced by an upward force exerted on you by the floor. This force is perpendicular to the floor and it is called the Normal Force N⃗ . Note that although N⃗  and W⃗  are equal and opposite, they do not constitute an action-reaction pair.Some other examples of static equilibrium are shown in the following figures.

        Application 1
        A block of mass 10 kg is suspended with two strings, as shown in the figure. Find the tensions T1 and T2  in the two strings.

        Solution:

        The free body diagram of the joint O is drawn as shown in the following figure.

        Applying equations for equilibrium.
                     ∑Fx=0T2sin30∘−T1=0                     ..(1)
        ∑Fy=0T2cos30∘−T1=0                  ..(2)
        Thus,     T2=100cos300=2003√N
        Substituting the value of T2 in equation (1), we get
        T1=T2sin30∘=1003√N

        Application 2

        Find the magnitude of the horizontal force F required to keep the block of mass m stationary on the smooth inclined plane as shown in the figure.

        Solution:

        The forces acting on the block are shown in the free body diagram.   Applying equations for equilibrium,
        ∑Fx=0Fcosθ−mgsinθ=0
        or       F=mgsinθcosθ=mgtanθ

        Prev Inertia and Non-Inertial Frames(Pseudo Force), Action-Reactin Pair, Monkey Problem
        Next NCERT Solutions – Laws of Motion

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