LAWS OF MOTION ONE SHOT CLASS 11 PHYSICS COMPLETE CHAPTER 🔥 FOR EXAM 2024-2025 || NEWTON'S LAW

Key Concepts

• Force: Push or pull.
• Inertia: A body's resistance to changes in its state of motion.
• Newton's Laws of Motion: Three fundamental laws governing motion.
• Momentum: Quantity of motion, defined as mass times velocity.
• Conservation of Momentum: In a closed system, total momentum remains constant.
• Impulse: Change in momentum, equal to force applied over a short time.
• FBD (Free Body Diagram): A diagram showing all forces acting on an object.
• Contact Force: Force requiring physical contact (e.g., normal reaction, friction).
• Non-Contact Force: Force acting at a distance (e.g., gravity).
• Normal Reaction: Force exerted by a surface perpendicular to the object in contact.
• Friction: Force opposing motion between surfaces in contact.
• Static Friction: Friction preventing initial motion.
• Kinetic Friction: Friction opposing motion of sliding objects.
• Coefficient of Friction (μ): A dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together.
• Angle of Friction: Angle between the normal force and the resultant force.
• Angle of Repose: Angle at which an object begins to slide down an inclined plane.
• Banking of Roads: Tilting roads on curves to assist turning.
• Centripetal Force: Force required to keep an object moving in a circular path.
• Tension: Force transmitted through a string or cable.
• Recoil Velocity: The velocity of a gun after firing a bullet.

Detailed Summary

1. Introduction to Newton's Laws

• The chapter will cover Newton's Laws of Motion in depth, aiming for understanding sufficient to solve JEE/NEET problems.
• Three levels of learning:
  • Level 1: Thoroughly cover each line of NCERT textbook.
  • Level 2: Solve high-quality problems.
  • Level 3: JEE/NEET level problems (dependent on completion of Levels 1 & 2).
• Directly jumping to advanced problems without foundational understanding leads to negative outcomes.

2. Force

• Definition: Any push or pull.
• What a Force Can Do:
  • Create motion in an object.
  • Bring a moving object to rest.
  • Change shape, size, or dimensions.
  • Change the direction of motion.

3. Inertia

• Definition: The inability or property of a body to resist changes in its state of motion.
• Real-world example: A car moving straight has inertia to continue moving straight.
• Types of Inertia:
  • Inertia of Rest: A body at rest tends to stay at rest.
  • Inertia of Motion: A body in motion tends to stay in motion.
  • Inertia of Direction: A body moving in a direction tends to stay in that direction.
• Examples:
  • A person in a bus falls forward when the brakes are applied due to inertia of motion.
  • Dust is removed from a blanket when beaten because the dust tends to stay at rest.
  • A coin placed on a card over a glass falls into the glass when the card is flicked away quickly.
• Historical Context: Galileo Galilei first proposed the concept of inertia.

4. Newton's First Law

• Statement: A body at rest stays at rest, and a body in motion stays in motion with the same speed and in the same direction unless acted upon by an external force.
• Also known as the Law of Inertia.
• Essentially restates the concept of inertia.

5. Momentum

• Definition: Amount or quantity of motion.
• Formula: Momentum (p) = mass (m) × velocity (v).
• Vector Quantity: Has both magnitude and direction.
• Significance: Indicates how "dangerous" an object is based on its mass and velocity.
• Examples:
  • A bullet has high momentum due to its high velocity.
  • A stationary truck has zero momentum despite its large mass.
• Calculations:
  • Calculating momentum given mass and velocity.
  • Calculating momentum using vector components (i, j, k).

6. Newton's Second Law

• Statement: The rate of change of momentum is directly proportional to the applied force.
• Formula: F = dp/dt (Force equals the rate of change of momentum).
• Mathematical Derivation:
  • F = k (Δp/Δt), where k is a constant (k=1).
  • F = Δp/Δt = (mv - mu)/t = m(v - u)/t = ma (since a = (v-u)/t).
• Conclusion: F = ma (Force equals mass times acceleration).
• Application: If a box with initial velocity zero is pushed, its velocity changes, indicating a change in momentum due to the applied force.

7. Impulse

• Definition: A large force applied over a short interval of time.
• Formula: Impulse (I) = Average Force × Time Taken.
• Impulse-Momentum Theorem: Impulse is equal to the change in momentum (I = Δp).
• Graphical Representation: The area under a force-time graph represents impulse.
• Examples:
  • Hitting a nail with a hammer.
  • A person catching a ball moves their hands backward to increase the time of impact, reducing the force.
• Calculations:
  • Calculating impulse given force and time.
  • Calculating impulse using change in momentum.
• Vector Form: Impulse is a vector quantity.

8. Newton's Third Law

• Statement: For every action, there is an equal and opposite reaction.
• Mathematical Representation: FAB = -FBA (Force on A due to B is equal and opposite to the force on B due to A).
• Examples:
  • A box on a bench exerts a force on the bench, and the bench exerts an equal and opposite force on the box.
  • A person walking pushes the ground backward, and the ground pushes the person forward.
• Action-Reaction Pairs: Forces always occur in pairs, acting on different objects.

9. Conservation of Momentum

• Definition: In the absence of external forces, the total momentum of a system remains constant.
• Condition: No external force should be applied.
• Formula: Initial momentum = Final momentum.
• Examples:
  • When a gun is fired, the bullet moves forward, and the gun recoils backward to conserve momentum.
  • When a person jumps out of a boat, the boat moves in the opposite direction to conserve momentum.
• Mathematical Representation: m1u1 + m2u2 = m1v1 + m2v2

10. Real Physics: Applying Newton's Second Law

• Net Force: The total force acting on an object.
• FBD (Free Body Diagram): A diagram showing all forces acting on an object.
• Types of Forces:
  • Contact Forces: Require physical contact (e.g., normal reaction, friction).
  • Non-Contact Forces: Act at a distance (e.g., gravity).
• Normal Reaction: Force exerted by a surface perpendicular to the object in contact.
• Force of Gravity: Force exerted by the Earth on an object (mg).
• Equilibrium: A state where the net force on an object is zero.
• FBD Examples:
  • A box on a table: Normal reaction upwards, gravity downwards.
  • A box on an inclined plane: Normal reaction perpendicular to the plane, gravity downwards.
• Component Breaking: Breaking forces into horizontal and vertical components.
• Motion with Newton's Second Law:
  • Fnet = ma (Net force equals mass times acceleration).
  • Applying this to various scenarios (e.g., a box being pushed, a box on an inclined plane).

11. Motion of Connected Bodies

• Tension: Force transmitted through a string or cable.
• Tension Direction: Always away from the body.
• Solving Problems:
  • Draw separate FBDs for each connected body.
  • Apply Newton's Second Law to each body.
  • Solve the resulting system of equations.
• Trick for Acceleration: a = Total External Force / Total Mass.

12. Circular Motion on Level Roads

• Centripetal Force: Force required to keep an object moving in a circular path.
• Friction's Role: On a level road, friction provides the necessary centripetal force.
• Maximum Safe Speed: v = √(μrg), where μ is the coefficient of friction, r is the radius of the curve, and g is the acceleration due to gravity.
• Safety Factors: Speed limits are often set lower than the calculated maximum safe speed.

13. Banking of Roads

• Purpose: To reduce reliance on friction and improve safety on curves.
• Method: Tilting the road surface inwards on curves.
• Force Analysis:
  • Normal reaction has horizontal and vertical components.
  • Horizontal component of normal reaction contributes to centripetal force.
• Maximum Safe Speed: v = √(rg (tan θ + μ) / (1 - μ tan θ)), where θ is the banking angle.
• Optimum Speed (No Friction): v = √(rg tan θ).

14. Angle of Friction

• Definition: The angle between the normal force and the resultant force.
• Formula: tan θ = μ (coefficient of friction).

15. Angle of Repose

• Definition: The angle at which an object begins to slide down an inclined plane.
• Relationship to Friction: tan θ = μ (coefficient of friction).

16. Recoil Velocity of a Gun

• Concept: When a gun is fired, the bullet moves forward, and the gun recoils backward to conserve momentum.
• Recoil Velocity: The velocity of the gun after firing a bullet.
• Conservation of Momentum: m1u1 + m2u2 = m1v1 + m2v2
• Calculation: By applying the conservation of momentum, the recoil velocity of the gun can be calculated.

17. Conclusion

• The chapter covers a wide range of topics related to Newton's Laws of Motion, from basic definitions to advanced applications.
• Understanding these concepts is crucial for solving problems in mechanics and related fields.
• Practice and revision are essential for mastering the material.