Course Content
Class 11 Physics Chapter 1 Physical World
Section Name Topic Name 1 Physical World 1.1 What is physics? 1.2 Scope and excitement of physics 1.3 Physics, technology and society 1.4 Fundamental forces in nature 1.5 Nature of physical laws
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Class 11 Physics Chapter 4 Motion In A Plane
4 Motion in a plane 4.1 Introduction 4.2 Scalars and vectors 4.3 Multiplication of vectors by real numbers 4.4 Addition and subtraction of vectors – graphical method 4.5 Resolution of vectors 4.6 Vector addition – analytical method 4.7 Motion in a plane 4.8 Motion in a plane with constant acceleration 4.9 Relative velocity in two dimensions 4.10 Projectile motion 4.11 Uniform circular motion
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Class 11 Physics Chapter 5 Laws of motion
Section Name Topic Name 5 Laws of motion 5.1 Introduction 5.2 Aristotle’s fallacy 5.3 The law of inertia 5.4 Newton’s first law of motion 5.5 Newton’s second law of motion 5.6 Newton’s third law of motion 5.7 Conservation of momentum 5.8 Equilibrium of a particle 5.9 Common forces in mechanics 5.10 Circular motion 5.11 Solving problems in mechanics
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Class 11 Physics Chapter 6 Work Energy and Power
Section Name Topic Name 6 Work Energy and power 6.1 Introduction 6.2 Notions of work and kinetic energy : The work-energy theorem 6.3 Work 6.4 Kinetic energy 6.5 Work done by a variable force 6.6 The work-energy theorem for a variable force 6.7 The concept of potential energy 6.8 The conservation of mechanical energy 6.9 The potential energy of a spring 6.10 Various forms of energy : the law of conservation of energy 6.11 Power 6.12 Collisions
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Class 11 Physics Chapter 7 Rotation motion
Topics Introduction Centre of mass Motion of COM Linear Momentum of System of Particles Vector Product Angular velocity Torque & Angular Momentum Conservation of Angular Momentum Equilibrium of Rigid Body Centre of Gravity Moment of Inertia Theorem of perpendicular axis Theorem of parallel axis Moment of Inertia of Objects Kinematics of Rotational Motion about a Fixed Axis Dynamics of Rotational Motion about a Fixed Axis Angular Momentum In Case of Rotation about a Fixed Axis Rolling motion
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Class 11 Physics Chapter 9 mechanics properties of solid
Section Name Topic Name 9 Mechanical Properties Of Solids 9.1 Introduction 9.2 Elastic behaviour of solids 9.3 Stress and strain 9.4 Hooke’s law 9.5 Stress-strain curve 9.6 Elastic moduli 9.7 Applications of elastic behaviour of materials
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Class 11 Physics Chapter 11 Thermal Properties of matter
Section Name Topic Name 11 Thermal Properties of matter 11.1 Introduction 11.2 Temperature and heat 11.3 Measurement of temperature 11.4 Ideal-gas equation and absolute temperature 11.5 Thermal expansion 11.6 Specific heat capacity 11.7 Calorimetry 11.8 Change of state 11.9 Heat transfer 11.10 Newton’s law of cooling
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Class 11 Physics Chapter 14 Oscillations
Section Name Topic Name 14 Oscillations 14.1 Introduction 14.2 Periodic and oscilatory motions 14.3 Simple harmonic motion 14.4 Simple harmonic motion and uniform circular motion 14.5 Velocity and acceleration in simple harmonic motion 14.6 Force law for simple harmonic motion 14.7 Energy in simple harmonic motion 14.8 Some systems executing Simple Harmonic Motion 14.9 Damped simple harmonic motion 14.10 Forced oscillations and resonance
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Class 11th Physics Online Class For 100% Result
About Lesson

Stress:-

  • Stress is the restoring force per unit area.
  • Whenever we apply an external force on the body to change its shape there is a restoring force that develops in the body in the opposite direction.
  • For example:-
    • When we apply an external force to a rubber ball at the same instant of time some force develops in the ball which acts in the opposite direction.
    • This opposite force which develops in the ball when an external force is applied is known as restoring force.
    • Both the forces are equal in magnitude.
  • Mathematically:-
  • Stress = F/A  
  • Where F= restoring force develops in the body because of force we apply.
  • A=area 
  • S.I. Unit :- N/m2 or Pascal(Pa)  
  • Dimensional formula is [ML–1T–2].

Types of StressLongitudinal stress

  • Longitudinal stress is defined as restoring force per unit area when the force is applied to the cross-sectional area of the cylindrical body. 
  • Consider a cylinder which we have to deform. If we apply the force perpendicular to the cross-sectional area, there will be a restoring force that develops in the cylinder in the opposite direction. 
  • This restoring force per unit area is known as longitudinal stress. 
  • Experimentally we can observe the increase in length. 
  • If we tie a heavy object to the cylinder with the help of threads. 
  • Let Initial length of the cylinder is L. 
  • After it gets stretched its length increases by ΔL due to the stress. 
  • As there is change in the length therefore this type of stress is known as longitudinal stress. 
  • In the below figure if we attach a box to the cylinder, a force is applied on the cross-sectional area of cylinder due to which it gets stretched and as a result there is change in the length of the cylinder.
mechanical properties of solids
mechanical properties of solids

Problem:- A 14.5 kg mass, fastened to the end of a steel wire of unstretched length 1.0 m, is whirled in a vertical circle with an angular velocity of 2 rev/s at the bottom of the circle. The cross-sectional area of the wire is 0.065 cm2. Calculate the elongation of the wire when the mass is at the lowest point of its path.

Answer:- Mass, m = 14.5 kg

Length of the steel wire, l = 1.0 m

Angular velocity, ω = 2 rev/s

Cross-sectional area of the wire, a = 0.065 cm2

Let Δl be the elongation of the wire when the mass is at the lowest point of its path.

When the mass is placed at the position of the vertical circle, the total force on the mass is:

F = mg + mlω2

= 14.5 × 9.8 + 14.5 × 1 × (2)2 = 200.1 N

Young’s modulus =Stress/Strain

Y = (F/A)/ Δl/l

= (F l)/A Δl

Therefore Δl = F l/A Y

Young’s modulus for steel = 2 × 1011 Pa

Therefore Δl = 200.1/0.065×10-4x2x1011 = 1539.23×107

=1.539×10-4m

Hence, the elongation of the wire is 1.539 × 10–4 m.

Types of Longitudinal Stress:-

  1. Tensile Stress
  2. Compressive Stress

Tensile Stress

  • Tensile stress is a longitudinal stress when the length of the cylinder increases.

For example:-

  • When the force is applied to both sides of the cylinder, the cylinder gets stretched. As a result there will be increase in its length.
mechanical properties of solids
mechanical properties of solids

Tangential or Shearing Stress

  • Restoring force per unit area when the force applied is parallel to the cross sectional area of the body.
  • Relative displacement occurs between the opposite faces of the body.
  • For example:-
  • Consider a cube. If we apply force parallel to the cross sectional area there will be movement which takes place between the opposite faces of the cube as they have relative motion with each other.
  • This type of stress is known as tangential or shearing stress.
mechanical properties of solids

Hydraulic Stress

  • Hydraulic stress is the restoring force per unit area when force is applied by a fluid on the body.
  • For example:-
  1. Consider a rubber ball and if it is dipped in the pond .Due to the pressure of water from all directions force acts on the ball as a result, the ball seems to be slightly contracted.
  2. Because of the force exerted by the water there is restoring force which develops in the ball which is equal in magnitude to the force applied by the water but in opposite direction.
  3. This type of stress is known as hydraulic stress.
mechanical properties of solids
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