Class 11 Physics NCERT Topics and Subtopics Index (2026 Updated)

NCERT Class 11 Physics Complete Contents, Chapters and Topics 

Complete chapter-wise index of NCERT Class 11 Physics with all topics and subtopics

Class 11 Physics NCERT – Contents

Front Matter

• Foreword
• Rationalisation of Content in the Textbooks
• Preface
• A Note for the Teacher

---

Chapter 1: Units and Measurements

1.1 Introduction
1.2 The International System of Units
1.3 Significant Figures
1.4 Dimensions of Physical Quantities
1.5 Dimensional Formulae and Dimensional Equations
1.6 Dimensional Analysis and Its Applications

---

Chapter 2: Motion in a Straight Line

2.1 Introduction
2.2 Instantaneous Velocity and Speed - 1, 2
2.3 Acceleration - 1 , 2
2.4 Kinematic Equations for Uniformly Accelerated Motion

---

Chapter 3: Motion in a Plane

3.1 Introduction
3.2 Scalars and Vectors
3.3 Multiplication of Vectors by Real Numbers
3.4 Addition and Subtraction of Vectors (Graphical Method)
3.5 Resolution of Vectors
3.6 Vector Addition (Analytical Method)
3.7 Motion in a Plane
3.8 Motion in a Plane with Constant Acceleration
3.9 Projectile Motion
3.10 Uniform Circular Motion

---

Chapter 4: Laws of Motion

4.1 Introduction
4.2 Aristotle's Fallacy
4.3 The Law of Inertia
4.4 Newton's First Law of Motion
4.5 Newton's Second Law of Motion
4.6 Newton's Third Law of Motion
4.7 Conservation of Momentum
4.8 Equilibrium of a Particle
4.9 Common Forces in Mechanics
4.10 Circular Motion
4.11 Solving Problems in Mechanics

---

Chapter 5: Work, Energy and Power

5.1 Introduction
5.2 Notions of Work and Kinetic Energy
5.3 Work
5.4 Kinetic Energy
5.5 Work-Energy Theorem
5.6 Potential Energy
5.7 Conservative and Non-Conservative Forces
5.8 Conservation of Mechanical Energy
5.9 Power
5.10 Collisions

---

Chapter 6: System of Particles and Rotational Motion

6.1 Introduction
6.2 Centre of Mass
6.3 Motion of Centre of Mass
6.4 Linear Momentum of a System of Particles
6.5 Vector Product of Two Vectors
6.6 Angular Velocity and Its Relation with Linear Velocity
6.7 Torque and Angular Momentum
6.8 Equilibrium of a Rigid Body
6.9 Centre of Gravity
6.10 Moment of Inertia
6.11 Theorems of Perpendicular and Parallel Axes
6.12 Kinematics of Rotational Motion about a Fixed Axis
6.13 Dynamics of Rotational Motion about a Fixed Axis
6.14 Angular Momentum in Case of Rotations about a Fixed Axis

---

Chapter 7: Gravitation

7.1 Introduction
7.2 Kepler's Laws
7.3 Universal Law of Gravitation
7.4 The Gravitational Constant
7.5 Acceleration due to Gravity of the Earth
7.6 Acceleration due to Gravity Below and Above the Surface of Earth
7.7 Gravitational Potential Energy
7.8 Escape Speed
7.9 Earth Satellites
7.10 Energy of an Orbiting Satellite
7.11 Geostationary and Polar Satellites

---

Chapter 8: Mechanical Properties of Solids

8.1 Introduction
8.2 Elastic Behaviour of Solids
8.3 Stress and Strain
8.4 Hooke's Law
8.5 Young's Modulus
8.6 Bulk Modulus
8.7 Shear Modulus
8.8 Applications of Elastic Behaviour of Materials

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Chapter 9: Mechanical Properties of Fluids

9.1 Introduction
9.2 Pressure
9.3 Streamline Flow
9.4 Bernoulli's Principle
9.5 Viscosity
9.6 Reynolds Number
9.7 Surface Tension
9.8 Applications of Surface Tension

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Chapter 10: Thermal Properties of Matter

10.1 Introduction
10.2 Temperature and Heat
10.3 Measurement of Temperature
10.4 Ideal-Gas Equation and Absolute Temperature
10.5 Thermal Expansion
10.6 Specific Heat Capacity
10.7 Calorimetry
10.8 Change of State
10.9 Heat Transfer

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Chapter 11: Thermodynamics

11.1 Introduction
11.2 Thermal Equilibrium
11.3 Zeroth Law of Thermodynamics
11.4 Heat, Internal Energy and Work
11.5 First Law of Thermodynamics
11.6 Specific Heat Capacity
11.7 Thermodynamic State Variables and Equation of State
11.8 Thermodynamic Processes
11.9 Heat Engines
11.10 Refrigerators and Heat Pumps
11.11 Second Law of Thermodynamics

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Chapter 12: Kinetic Theory

12.1 Introduction
12.2 Molecular Nature of Matter
12.3 Behaviour of Gases
12.4 Kinetic Theory of an Ideal Gas
12.5 Law of Equipartition of Energy
12.6 Specific Heat Capacity
12.7 Mean Free Path

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Chapter 13: Oscillations

13.1 Introduction
13.2 Periodic and Oscillatory Motions
13.3 Simple Harmonic Motion
13.4 Simple Harmonic Motion and Uniform Circular Motion
13.5 Velocity and Acceleration in SHM
13.6 Force Law for SHM
13.7 Energy in SHM
13.8 Oscillations of a Spring
13.9 Simple Pendulum

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Chapter 14: Waves

14.1 Introduction
14.2 Transverse and Longitudinal Waves
14.3 Displacement Relation in a Progressive Wave
14.4 Speed of a Travelling Wave
14.5 Principle of Superposition of Waves
14.6 Reflection of Waves
14.7 Standing Waves and Normal Modes
14.8 Beats
14.9 Doppler Effect

Total Chapters: 14 

Internal Links

1. NCERT Class 11 Physics Notes Chapter Wise

2. Class 11 Physics Important Formulas PDF

3. NCERT Class 11 Physics Solutions

4. Class 11 Physics Chapter-wise MCQs

5. NCERT Class 11 Physics Previous Year Questions

6. Complete Class 11 Science Syllabus

7. Class 11 Chemistry NCERT Contents

8. Class 11 Mathematics NCERT Contents

9. CBSE Class 11 Study Plan

10. Physics Revision Notes for Class 11

Example 4.7 Maximum Acceleration of a Train Solved Step by Step

 Maximum Acceleration of a Train Using Static Friction Explained

-  Dr.Sanjaykumar Pawar 

A box remains stationary inside an accelerating train due to static friction acting between the box and the train floor.

 

Example 4.7 Determine the maximum acceleration of the train in which a box lying on its floor will remain stationary,given that the co-efficient of static friction between the box and the train’s floor is 0.15.

Example 4.7

Question:
Determine the maximum acceleration of a train in which a box lying on its floor will remain stationary, given that the coefficient of static friction between the box and the train's floor is 0.15.

Step 1: Understand the Concept

When the train accelerates, the box must also accelerate along with the train.

The force responsible for accelerating the box is the static friction between the box and the floor.

• If friction is enough, the box remains stationary relative to the train.
• If friction is not enough, the box starts sliding backward.

Therefore, the maximum acceleration depends on the maximum static friction available.

Step 2: Apply Newton's Second Law

According to Newton's Second Law:

F = ma

The only horizontal force acting on the box is static friction (f_s).

ma = f_s

Step 3: Write Maximum Static Friction

Maximum static friction is given by:

f_s ≤ μ_sN

where:

• μ_s = coefficient of static friction
• N = normal reaction

Step 4: Find the Normal Reaction

Since the box is resting on a horizontal floor:

N = mg

Substitute N = mg into the friction formula:

f_s ≤ μ_smg

Step 5: Substitute into Newton's Law

From Newton's Law:

ma = f_s

Using the maximum friction condition:

ma ≤ μ_smg

Cancel mass (m) from both sides:

a ≤ μ_sg

Therefore:

a_max = μ_sg

Step 6: Substitute the Given Values

Given:

μ_s = 0.15

g = 10 m/s²

Substitute into the formula:

a_max = 0.15 × 10

a_max = 1.5 m/s²

Final Answer:

a_max = 1.5 m/s²

Quick Notes for Beginners

• Static friction helps the box move with the train.
• Maximum static friction = μ_sN.
• For a horizontal surface, N = mg.
• Using F = ma, we get:

ma = μ_smg

a = μ_sg

a = 0.15 × 10 = 1.5 m/s²

Hence, the train can accelerate up to 1.5 m/s² without the box sliding.

Newton's Third Law of Motion Explained with Examples for Class 11

 Newton's Third Law: CBSE Class 11 Physics Complete Guide

Newton’s Third Law of Motion – Easy NEET Notes (Line-by-Line Explanation)

Newton's Third Law of Motion: Every action force has an equal and opposite reaction force acting simultaneously on another body.

- Dr.Sanjaykumar pawar

Introduction

• Newton’s Second Law tells us how an external force causes acceleration.
• But a question arises: Where does this external force come from?
• In Newtonian mechanics, an external force always comes from another body or object.

---

Understanding Force Between Two Bodies

• Consider two bodies: A and B.
• If body B exerts a force on A, we may ask:
  • Does A also exert a force on B?
• Newton's answer is Yes.

Example 1: Spring and Hand

• When you press a spring, your hand exerts force on the spring.
• The spring gets compressed.
• At the same time, the spring pushes back on your hand.
• You can feel this force.

Example 2: Earth and Stone

• Earth pulls a stone downward due to gravity.
• We may not notice it, but the stone also pulls the Earth upward.
• The force exerted by the stone on Earth is equal in magnitude.
• Since Earth is extremely massive, its acceleration is very small and difficult to observe.

---

Newton's Third Law of Motion

Statement

"To every action, there is always an equal and opposite reaction."

OR

"For every force, there is an equal and opposite force acting on another body."

---

Mathematical Form

Where:

• = Force on A by B
• = Force on B by A
• Negative sign (−) shows opposite direction.

---

Main Idea of Third Law

• Force never exists alone.
• Forces always occur in pairs.
• Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on the first body.
• These two forces are called an action-reaction pair.

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Important Points for NEET

Point 1: Action and Reaction Are Both Forces

• The words action and reaction simply mean forces.
• There is no special difference between them.
• A better statement is:

"Force on A by B is equal and opposite to force on B by A."

---

Point 2: Action Does Not Come Before Reaction

Common Misconception

• Many students think action happens first and reaction happens later.

Correct Concept

• Action and reaction occur simultaneously.
• They act at the same instant.
• Neither force is the cause nor the effect of the other.

Example

• When you hit a wall:
  • Your hand exerts force on the wall.
  • The wall exerts force on your hand at exactly the same moment.

---

Point 3: Action and Reaction Act on Different Bodies

Very Important NEET Point

• Action and reaction never act on the same body.
• They always act on two different bodies.

Example

Person pushes wall:

Force	Acts On
Person pushes wall	Wall
Wall pushes person	Person

• Since they act on different bodies, they cannot cancel each other.

---

Why Action and Reaction Do Not Cancel?

Example

Suppose:

• You push a wall with 100 N force.
• Wall pushes you back with 100 N force.

Students often say:

Net force = 100 N − 100 N = 0

This is wrong.

Reason

• 100 N force acts on the wall.
• 100 N reaction force acts on you.
• Since they act on different bodies, they cannot be added together.

---

Internal Forces in a System

Consider System (A + B)

• Here, force on A by B and force on B by A are internal forces.
• Internal forces always occur in equal and opposite pairs.
• Therefore, they cancel each other when considering the whole system.

Result

• Internal forces do not affect the motion of the entire system.
• Only external forces can change the motion of a system.

---

Real-Life Examples of Newton’s Third Law

1. Walking

• Foot pushes the ground backward.
• Ground pushes the foot forward.
• This forward reaction helps us walk.

2. Swimming

• Swimmer pushes water backward.
• Water pushes swimmer forward.

3. Rocket Launch

• Rocket throws gases downward.
• Gases push rocket upward.

4. Gun Recoil

• Bullet moves forward.
• Gun experiences backward recoil.

5. Jumping

• Person pushes ground downward.
• Ground pushes person upward.

---

NEET Quick Revision Points

✅ Force always occurs in pairs.

✅ Action and reaction are equal in magnitude.

✅ Action and reaction are opposite in direction.

✅ They act simultaneously.

✅ They act on different bodies.

✅ They never cancel each other on a single body.

✅ Internal forces cancel within a system.

✅ Only external forces can change the motion of a system.

---

One-Line NEET Definition

Newton’s Third Law states that whenever one body exerts a force on another body, the second body simultaneously exerts an equal and opposite force on the first body.

NEWTON'S THIRD LAW OF MOTION – CBSE CLASS 11 QUESTION BANK

A. Multiple Choice Questions (MCQs)

1. Newton's Third Law states that:

(a) Force is proportional to acceleration (b) Every object remains at rest (c) To every action there is an equal and opposite reaction (d) Momentum is conserved

Answer: (c)

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2. Action and reaction forces:

(a) Act on the same body (b) Act on different bodies (c) Are unequal (d) Act at different times

Answer: (b)

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3. Which of the following is an example of Newton's Third Law?

(a) Falling of an apple (b) Walking on the ground (c) Inertia of rest (d) Motion of planets

Answer: (b)

---

4. The force exerted by Earth on a stone and by the stone on Earth are:

(a) Unequal (b) Equal and opposite (c) Same direction (d) Zero

Answer: (b)

---

5. Action and reaction forces:

(a) Cancel each other (b) Act simultaneously (c) Are internal forces only (d) Produce no motion

Answer: (b)

---

B. Very Short Answer Questions (1 Mark)

1. State Newton's Third Law of Motion.

Answer: To every action, there is always an equal and opposite reaction.

2. Do action and reaction act on the same body?

Answer: No, they act on different bodies.

3. What is the direction of reaction force?

Answer: Opposite to the action force.

4. Can action and reaction occur separately?

Answer: No, they always occur together.

5. Give one example of Newton's Third Law.

Answer: Walking on the ground.

---

C. Short Answer Questions (2–3 Marks)

1. Why can a person walk on the ground?

Answer: The foot pushes the ground backward. The ground exerts an equal and opposite force on the foot in the forward direction. This reaction force enables the person to walk.

---

2. Why does a gun recoil when fired?

Answer: When the bullet moves forward, it exerts an equal and opposite force on the gun. As a result, the gun moves backward, called recoil.

---

3. Explain why action and reaction forces do not cancel each other.

Answer: Action and reaction forces act on different bodies. Since they act on different objects, they cannot be added together and therefore do not cancel each other.

---

4. What are internal forces?

Answer: Internal forces are forces acting between particles of the same system. They occur in equal and opposite pairs and cancel each other.

---

D. Long Answer Questions (5 Marks)

1. State and explain Newton's Third Law of Motion with examples.

Answer: Newton's Third Law states that to every action there is always an equal and opposite reaction.

Characteristics:

1. Forces always occur in pairs.
2. Action and reaction are equal in magnitude.
3. They are opposite in direction.
4. They act simultaneously.
5. They act on different bodies.

Examples: • Walking • Swimming • Rocket propulsion • Gun recoil • Jumping from a boat

Thus, every force in nature has an equal and opposite counterpart.

---

2. Explain rocket propulsion using Newton's Third Law.

Answer: A rocket expels hot gases downward at high speed. The gases exert a downward force. According to Newton's Third Law, the gases exert an equal and opposite force on the rocket. This upward reaction force propels the rocket upward.

---

E. Assertion and Reason Questions

1.

Assertion (A): Action and reaction forces are equal and opposite.

Reason (R): They act on the same body.

Answer: Assertion is true but Reason is false.

---

2.

Assertion (A): A swimmer moves forward in water.

Reason (R): Water pushes the swimmer forward when the swimmer pushes water backward.

Answer: Both A and R are true and R is the correct explanation.

---

3.

Assertion (A): Action and reaction occur simultaneously.

Reason (R): There is no cause-effect relationship between them.

Answer: Both A and R are true and R is the correct explanation.

---

F. Fill in the Blanks

1. Newton's Third Law states that every action has an equal and ______ reaction.

Answer: opposite

2. Action and reaction forces act on ______ bodies.

Answer: different

3. Walking is possible because of the ______ force of the ground.

Answer: reaction

4. Forces always occur in ______.

Answer: pairs

5. Internal forces of a system ______ each other.

Answer: cancel

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G. Statement-Based Questions

1. Identify True or False:

(a) Action and reaction act on different bodies. Answer: True

(b) Action occurs before reaction. Answer: False

(c) Forces always occur in pairs. Answer: True

(d) Action and reaction can cancel each other. Answer: False

(e) Rocket propulsion is based on Newton's Third Law. Answer: True

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H. Match the Columns

Column A

A. Walking

B. Gun

C. Rocket

D. Swimming

Column B

1. Water pushes swimmer

2. Ground pushes person

3. Gases push rocket upward

4. Recoil

Answers

A → 2

B → 4

C → 3

D → 1

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I. Case Study Questions

Case Study

A student pushes a wall with a force of 50 N. The wall exerts a force of 50 N on the student. The student notices that the wall does not move.

Questions

1. Which law explains this situation?

Answer: Newton's Third Law of Motion.

2. What is the reaction force?

Answer: Force exerted by the wall on the student.

3. Are action and reaction equal?

Answer: Yes.

4. Why does the wall not move?

Answer: Because the wall is firmly supported and its acceleration is negligible.

5. Do action and reaction act on the same body?

Answer: No.

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J. Important One-Mark CBSE Questions

1. Define action-reaction pair.
2. Give one example of Newton's Third Law.
3. Why does a boat move backward when a person jumps forward?
4. Why does a rocket move upward?
5. Can action exist without reaction?

Answers

1. Pair of equal and opposite forces acting on different bodies.
2. Walking.
3. Due to equal and opposite reaction force.
4. Due to reaction force of escaping gases.
5. No.

NEWTON'S THIRD LAW OF MOTION
│
├── Definition
│   │
│   └── To every action,
│       there is an equal
│       and opposite reaction.
│
├── Main Idea
│   │
│   ├── Force never exists alone
│   ├── Forces occur in pairs
│   └── Mutual interaction between bodies
│
├── Mathematical Form
│   │
│   └── FAB = -FBA
│
├── Action & Reaction
│   │
│   ├── Equal magnitude
│   ├── Opposite direction
│   ├── Act simultaneously
│   └── Act on different bodies
│
├── Important Points
│   │
│   ├── Action = Force
│   ├── Reaction = Force
│   ├── No cause-effect relation
│   ├── No time gap between them
│   └── Cannot cancel each other
│       on a single body
│
├── Internal Forces
│   │
│   ├── Present within a system
│   ├── Equal and opposite
│   └── Cancel each other
│
├── Examples
│   │
│   ├── Walking
│   │   ├── Foot pushes ground
│   │   └── Ground pushes foot
│   │
│   ├── Swimming
│   │   ├── Swimmer pushes water
│   │   └── Water pushes swimmer
│   │
│   ├── Rocket
│   │   ├── Gases move downward
│   │   └── Rocket moves upward
│   │
│   ├── Gun Recoil
│   │   ├── Bullet forward
│   │   └── Gun backward
│   │
│   └── Jumping
│       ├── Person pushes ground
│       └── Ground pushes person
│
└── NEET Revision
    │
    ├── Forces occur in pairs
    ├── Equal magnitude
    ├── Opposite direction
    ├── Simultaneous action
    ├── Different bodies
    ├── Do not cancel on one body
    └── Internal forces cancel 

INTERNAL LINKS
Newton's First Law of Motion Notes
Newton's Second Law of Motion Explained
Laws of Motion Complete Chapter Notes
Force and Inertia Class 11 Physics
Momentum and Impulse Notes
Conservation of Momentum
Friction Class 11 Physics
Work, Energy and Power Notes
Circular Motion Class 11 Physics
NEET Physics Important Questions
CBSE Class 11 Physics MCQ Bank
Physics Formula Sheet for Class 11
Motion in a Straight Line Notes
Motion in a Plane Notes
Gravitation Complete Notes

Newton's Second Law Notes for Class 11 Physics | CBSE & NEET Guide

 Newton's Second Law Explained: Projectile Motion and Force Components 

Easy Notes (NEET Level) – Important Points from Newton’s Second Law 

- Dr.Sanjaykumar pawar

1. Component of Velocity Normal (Perpendicular) to the Force Remains Unchanged

• A force can only change the velocity component in its own direction.
• The velocity component perpendicular (normal) to the force does not change.
• This is because there is no acceleration in the perpendicular direction.

Example: Projectile Motion

• In projectile motion, only gravitational force acts on the particle.
• Gravity acts vertically downward.
• Therefore, acceleration is only in the vertical direction.
• There is no horizontal force acting on the projectile (neglecting air resistance).
• Hence, the horizontal component of velocity remains constant throughout the motion.
• Only the vertical component of velocity changes due to gravity.

Key NEET Point:
Force changes velocity only along its direction; perpendicular velocity remains unchanged.

---

2. Newton's Second Law for a Single Particle

• Newton's second law is written as:

• Here, F is the net external force acting on the particle.
• a is the acceleration produced in the particle.
• This form is directly applicable to a single point particle.

Key NEET Point:
Always use the net external force, not individual forces separately.

---

3. Newton's Second Law for a System of Particles

• The same law can also be applied to:

  • A rigid body
  • A group of particles (system)

• In such cases:

  • F = total external force on the system.
  • a = acceleration of the centre of mass of the system.

• Internal forces between particles of the system are not included.

• Internal forces cancel each other and do not affect the motion of the whole system.

Example

• Two blocks connected by a string.
• Tension between the blocks is an internal force.
• Only external forces like gravity or an applied pull are considered.

Key NEET Point:
For a system, consider only external forces; ignore internal forces.

---

4. Acceleration Depends on Present Force Only

• Acceleration at any instant is determined by the force acting at that same instant.
• Past motion does not affect present acceleration.
• A particle has no "memory" of its previous motion.

Example: Stone Dropped from an Accelerated Train

• A train is moving with acceleration.

• A stone is dropped from the train.

• Immediately after release:

  • The stone is no longer connected to the train.
  • No horizontal force acts on the stone (ignoring air resistance).
  • Therefore, horizontal acceleration becomes zero.

• The stone keeps its horizontal velocity but does not keep the train's acceleration.

Key NEET Point:
Velocity may continue, but acceleration changes instantly according to the force acting at that moment.

---

5. Newton's Second Law is a Local Relation

• Newton's second law is called a local relation.
• It relates force and acceleration at the same place and same time.

Meaning

• Force acting here and now determines acceleration here and now.
• Previous positions, velocities, or accelerations do not directly determine present acceleration.
• Only the current force matters.

Key NEET Point:
Present acceleration depends only on present force, not on the history of motion.

---

Quick Revision for NEET

1. Force changes velocity only in its own direction.
2. Velocity perpendicular to force remains unchanged.
3. In projectile motion, horizontal velocity remains constant.
4. Newton's second law: .
5. For a system, use total external force only.
6. Internal forces are ignored.
7. Acceleration depends on the force acting at that instant.
8. A body has no memory of past acceleration.
9. Newton's second law is a local relation.
10. Present force determines present acceleration.  

Newton's Second Law explains how force produces acceleration and why horizontal velocity remains constant in projectile motion.

CBSE Class 11 Physics – Newton's Second Law (Important Questions with Answers)

A. MCQs (1 Mark Each)

1. In projectile motion, the horizontal component of velocity remains constant because:

a) Gravity acts horizontally
b) No horizontal force acts on the projectile
c) Air resistance is maximum
d) Vertical velocity is constant

Answer: (b) No horizontal force acts on the projectile

---

2. The force in Newton's second law represents:

a) Internal force
b) External force
c) Gravitational force only
d) Friction only

Answer: (b) External force

---

3. For a system of particles, acceleration refers to the acceleration of:

a) Any particle
b) Largest particle
c) Centre of mass
d) Geometric centre

Answer: (c) Centre of mass

---

4. Internal forces are:

a) Included in net external force
b) Ignored while applying Newton's second law to a system
c) Greater than external forces
d) Always zero

Answer: (b)

---

5. A body remembers:

a) Past acceleration
b) Past force
c) Present force only affects acceleration
d) Future force

Answer: (c)

---

B. Very Short Answer Questions (1 Mark)

1. What is meant by the net force on a particle?

Answer: The vector sum of all external forces acting on the particle.

---

2. Which velocity component remains unchanged in projectile motion?

Answer: Horizontal component of velocity.

---

3. What is the SI unit of force?

Answer: Newton (N).

---

4. Which force is not included while applying Newton's second law to a system?

Answer: Internal force.

---

5. What is meant by a local relation?

Answer: A relation that connects physical quantities at the same place and same instant.

---

C. Short Answer Questions (2–3 Marks)

1. Why does the horizontal velocity of a projectile remain constant?

Answer:

• Gravity acts vertically downward.
• No horizontal force acts on the projectile.
• Therefore, horizontal acceleration is zero.
• Hence, horizontal velocity remains constant.

---

2. What is the role of internal forces in a system?

Answer:

• Internal forces act between particles of the same system.
• They cancel each other in pairs.
• Therefore, they do not affect the motion of the system as a whole.

---

3. Explain why a stone dropped from an accelerating train has no horizontal acceleration.

Answer:

• After release, the stone is no longer connected to the train.
• No horizontal force acts on it.
• According to Newton's second law, acceleration depends on force.
• Hence horizontal acceleration becomes zero.

---

D. Long Answer Questions (3–5 Marks)

1. Explain Newton's second law for a system of particles.

Answer: Newton's second law states that the net external force acting on a body equals the product of its mass and acceleration.

For a system of particles:

• F represents the total external force on the system.
• a represents the acceleration of the centre of mass.
• Internal forces are not included because they cancel each other.
• The motion of the entire system depends only on external forces.

---

2. Explain why Newton's second law is called a local relation.

Answer:

• Force and acceleration are related at the same place and same instant.
• Present acceleration depends only on present force.
• Past motion does not influence present acceleration directly.
• A body has no memory of previous forces or accelerations.
• Therefore Newton's second law is called a local relation.

---

E. Assertion and Reason Questions

1.

Assertion (A): Horizontal velocity remains constant in projectile motion.

Reason (R): No horizontal force acts on the projectile.

Answer: Both A and R are true, and R is the correct explanation of A.

---

2.

Assertion (A): Internal forces are included in the net force acting on a system.

Reason (R): Internal forces cancel each other.

Answer: Assertion is false, Reason is true.

---

3.

Assertion (A): A body remembers its previous acceleration.

Reason (R): Present acceleration depends only on present force.

Answer: Assertion is false, Reason is true.

---

F. Fill in the Blanks

1. In projectile motion, the ________ component of velocity remains constant. Answer: horizontal

2. Newton's second law relates force and ________. Answer: acceleration

3. For a system, acceleration refers to the acceleration of the ________. Answer: centre of mass

4. Internal forces are ________ while applying Newton's second law to a system. Answer: ignored

5. Present acceleration depends on ________ force. Answer: present

---

G. True or False

1. Gravity changes the horizontal velocity of a projectile. Answer: False

2. Internal forces affect the motion of the centre of mass. Answer: False

3. External force determines acceleration. Answer: True

4. Newton's second law is a local relation. Answer: True

5. A body remembers its past acceleration. Answer: False

---

H. Match the Columns

Column A	Column B
1. Projectile motion	(a) Centre of mass
2. System acceleration	(b) Horizontal velocity constant
3. Internal forces	(c) Present force
4. Local relation	(d) Ignored
5. Acceleration depends on	(e) Same place and time

Answers

1 → (b)
2 → (a)
3 → (d)
4 → (e)
5 → (c)

---

I. Statement-Based Questions

Statement 1:

A projectile is moving in air with negligible air resistance.

Statement 2:

Its horizontal velocity remains constant.

a) Both statements are true and Statement 2 explains Statement 1.
b) Both statements are true but Statement 2 does not explain Statement 1.
c) Statement 1 is true, Statement 2 is false.
d) Statement 1 is false, Statement 2 is true.

Answer: (a)

---

J. Case Study Questions (4 Marks)

Case Study

A train is moving with acceleration. A stone is dropped from the train. Immediately after release, the stone continues moving forward but experiences only gravitational force.

Questions

1. Which force acts on the stone after release?

Answer: Gravitational force.

2. What is the horizontal acceleration of the stone?

Answer: Zero.

3. Why does the stone continue moving horizontally?

Answer: Due to its existing horizontal velocity.

4. What does this example prove about Newton's second law?

Answer: Present acceleration depends only on present force and not on past motion.

---

Exam-Oriented One-Line Revision

• Force changes velocity only in its own direction.
• Velocity perpendicular to force remains unchanged.
• Horizontal velocity remains constant in projectile motion.
• Only external forces are considered for a system.
• Internal forces cancel each other.
• Acceleration of a system is acceleration of its centre of mass.
• Present force determines present acceleration.
• Newton's second law is a local relation.

NEWTON'S SECOND LAW – IMPORTANT POINTS

│

├── 1. Velocity Component Perpendicular to Force

│   │

│   ├── Force changes velocity only along its direction

│   ├── No acceleration perpendicular to force

│   ├── Perpendicular (normal) velocity remains constant

│   │

│   └── Example: Projectile Motion

│       │

│       ├── Gravity acts vertically downward

│       ├── Vertical velocity changes

│       ├── No horizontal force (air resistance neglected)

│       └── Horizontal velocity remains constant

│

├── 2. Newton's Second Law for a Particle

│   │

│   ├── F = ma

│   ├── F = Net external force

│   ├── a = Acceleration produced

│   └── Applicable to a single particle

│

├── 3. Newton's Second Law for a System

│   │

│   ├── Applicable to

│   │   ├── Rigid body

│   │   └── System of particles

│   │

│   ├── F = Total external force

│   ├── a = Acceleration of centre of mass

│   │

│   └── Internal Forces

│       │

│       ├── Not included in F

│       ├── Cancel each other

│       └── Do not affect system motion

│

├── 4. Acceleration Depends on Present Force

│   │

│   ├── Present force → Present acceleration

│   ├── Past motion does not matter

│   └── Body has no memory of past acceleration

│

├── 5. Example: Stone Dropped from Accelerated Train

│   │

│   ├── Train is accelerating

│   ├── Stone is released

│   ├── Connection with train ends

│   ├── No horizontal force on stone

│   ├── Horizontal acceleration = 0

│   └── Horizontal velocity continues unchanged

│

├── 6. Local Nature of Newton's Second Law

│   │

│   ├── Local Relation

│   │

│   ├── Force at a point

│   │       ↓

│   ├── Determines acceleration

│   │       ↓

│   └── At the same place and same time

│

└── NEET QUICK FACTS

    │

    ├── Force changes velocity only in its direction

    ├── Perpendicular velocity remains unchanged

    ├── Horizontal velocity is constant in projectile motion

    ├── F = ma

    ├── Use only external forces for a system

    ├── Ignore internal forces

    ├── Present force determines present acceleration

    ├── No memory of previous acceleration

    └── Newton's second law is a local relation 

Aristotle's Fallacy Explained | Laws of Motion Class 11 Physics

 Aristotle's Fallacy Class 11 Physics Notes, MCQs & Questions Answers

- Dr.Sanjaykumar Pawar 

4.2 ARISTOTLE'S FALLACY – Easy Line-by-Line Notes (NEET Level)

Introduction

• One important question in physics is: "Is a force required to keep a body moving?"
• Today the answer seems simple.
• But scientists took many centuries to find the correct answer.
• The correct explanation was given by in the 17th century.
• Galileo's ideas became the foundation of Newtonian Mechanics.
• These ideas marked the beginning of modern science.

---

Aristotle's View About Motion

• was a Greek philosopher who lived from 384 BC to 322 BC.

• Aristotle believed that:

  "A moving object needs a continuous external force to keep moving."

• According to him, if the force is removed, the object should stop moving.

Example Given by Aristotle

• Consider an arrow shot from a bow.
• Aristotle thought the arrow continues moving because:
  • Air behind the arrow keeps pushing it forward.
• Therefore, he concluded that motion needs a continuous force.

---

Aristotle's Law of Motion

Aristotle's idea can be written as:

Aristotle's Law

"An external force is required to keep a body in motion."

---

Why Did Aristotle Think So?

• Aristotle's conclusion came from everyday observations.
• In daily life, moving objects eventually stop.

Examples

• A toy car stops after some time.

• A bicycle slows down if we stop pedaling.

• A rolling ball finally comes to rest.

• Therefore, it appeared that:

  • Continuous force is necessary for continuous motion.

• Even a small child notices this fact.

Example: Toy Car

• A child pulls a toy car using a string.

• The toy car moves only while the child keeps pulling.

• When the child stops pulling:

  • The toy car eventually stops.

• This observation seems to support Aristotle's idea.

---

What Was the Mistake in Aristotle's Argument?

• Aristotle ignored an important force:

  Friction

• Friction always acts opposite to the direction of motion.

• Friction tries to slow down moving objects.

Example

• When a toy car moves on the floor:
  • Friction acts between the wheels and the floor.
  • Friction opposes motion.
  • Because of friction, the car slows down and stops.

---

Role of the Child's Force

• To keep the toy car moving:
  • The child must continuously pull it.
• The pulling force balances the frictional force.

During Uniform Motion

When the toy car moves with constant speed:

Child's Pulling Force = Frictional Force

Therefore,

Net Force = 0

• The forces cancel each other.
• The car continues moving with constant speed.

---

What If Friction Were Absent?

Imagine a perfectly smooth floor.

Then:

• No friction would act on the toy car.
• The child would give one pull.
• After that, no force would be needed.
• The toy car would continue moving with constant speed.

Important Conclusion

Force is not required to maintain uniform motion.

Force is required only to change motion.

---

Friction and Viscous Force

In the real world, opposing forces are almost always present.

In Solids

• Opposing force = Friction

Examples:

• Ball rolling on the ground
• Toy car moving on a floor

In Fluids (Liquids and Gases)

• Opposing force = Viscous Force (Drag)

Examples:

• Boat moving in water
• Air resistance on a moving car

---

Why Aristotle Was Wrong

• Aristotle observed real-life motion correctly.
• But he misunderstood the reason objects stop.
• He thought objects stop because force is absent.
• Actually, objects stop because friction opposes motion.

His Mistake

He ignored frictional forces.

---

Galileo's Great Contribution

• Galileo imagined an ideal world without friction.

• He asked:

  "What would happen if no opposing force existed?"

• He concluded:

Galileo's Conclusion

A body in uniform motion will continue moving uniformly unless an external force changes its motion.

• This idea later became:
  • Law of Inertia
  • Newton's First Law of Motion

---

NEET Quick Facts

Aristotle Said

❌ Force is needed to keep a body moving.

Galileo Said

✅ Force is needed only to change the state of motion.

Real Reason Objects Stop

✅ Friction

If Friction Were Zero

✅ A moving body would continue moving with constant velocity.

Foundation of Newton's First Law

✅ Galileo's concept of inertia

---

One-Line Revision

• Aristotle believed continuous force is required for continuous motion.
• His idea was based on everyday observations.
• He ignored the effect of friction.
• Friction opposes motion and causes objects to stop.
• Galileo showed that without friction, a body would keep moving uniformly.
• This led to the Law of Inertia and Newton's First Law of Motion. ✅  

Aristotle's Fallacy Explained: How Galileo Corrected the Ancient Theory of Motion and Laid the Foundation of Modern Physics.

Class 11 Physics – Aristotle's Fallacy Question Bank (CBSE & NEET Level)

A. Multiple Choice Questions (MCQs)

1. Who proposed the idea that a force is required to keep a body in motion?

a) Newton
b) Galileo
c) Aristotle
d) Einstein

Answer: (c) Aristotle

---

2. Aristotle lived during:

a) 1642–1727 AD b) 384 BC–322 BC c) 1564–1642 AD d) 1879–1955 AD

Answer: (b) 384 BC–322 BC

---

3. According to Aristotle, a moving body:

a) Moves forever without force b) Needs a continuous external force to keep moving c) Stops immediately d) Accelerates continuously

Answer: (b) Needs a continuous external force to keep moving

---

4. What was the major flaw in Aristotle's argument?

a) Ignoring gravity b) Ignoring friction c) Ignoring velocity d) Ignoring mass

Answer: (b) Ignoring friction

---

5. The correct explanation of motion without friction was given by:

a) Aristotle b) Archimedes c) Galileo d) Kepler

Answer: (c) Galileo

---

6. A toy car comes to rest mainly because of:

a) Gravity b) Magnetism c) Friction d) Tension

Answer: (c) Friction

---

7. Friction acts:

a) Along the motion b) Opposite to motion c) Vertically upward d) Vertically downward

Answer: (b) Opposite to motion

---

8. Galileo imagined a world:

a) Without gravity b) Without mass c) Without friction d) Without motion

Answer: (c) Without friction

---

B. Very Short Answer Questions (1 Mark)

1. Who gave the correct answer to the problem of motion?

Answer: Galileo.

---

2. State Aristotle's law of motion.

Answer: An external force is required to keep a body in motion.

---

3. What force did Aristotle ignore?

Answer: Frictional force.

---

4. Which force opposes motion?

Answer: Frictional force.

---

5. What is viscous force?

Answer: The force that opposes motion in fluids.

---

6. Name the scientist who laid the foundation of Newtonian mechanics.

Answer: Galileo.

---

C. Short Answer Questions (2–3 Marks)

1. Why did Aristotle think force is needed to keep a body moving?

Answer: Aristotle observed that moving objects eventually come to rest. He concluded that continuous force is needed to maintain motion. He did not consider the effect of friction.

---

2. Explain the toy car example used to describe Aristotle's fallacy.

Answer: A toy car moves when pulled by a child. When the child stops pulling, the car stops because friction acts opposite to motion. Aristotle incorrectly thought the car stopped due to the absence of force.

---

3. What is the role of friction in Aristotle's fallacy?

Answer: Friction opposes the motion of objects and slows them down. Aristotle ignored friction and wrongly concluded that force is necessary to maintain motion.

---

4. What happens if friction is absent?

Answer: In the absence of friction, a moving body would continue moving with constant velocity without requiring any external force.

---

D. Long Answer Questions (5 Marks)

1. Explain Aristotle's fallacy and Galileo's correction.

Answer:

Aristotle believed that a body requires continuous external force to keep moving. He based this idea on everyday observations where moving objects eventually stop.

For example, a toy car stops when the child stops pulling it.

The flaw in Aristotle's argument was that he ignored friction. Friction acts opposite to motion and causes moving objects to stop.

Galileo imagined an ideal world without friction. He concluded that a moving body would continue moving with constant velocity even without any external force.

This idea became the foundation of the Law of Inertia and Newton's First Law of Motion.

---

2. Explain how friction led Aristotle to an incorrect conclusion.

Answer:

In daily life, all moving objects experience friction. Because of friction, they gradually slow down and stop.

Aristotle observed this behavior and concluded that motion requires continuous force.

However, the actual reason for stopping is friction, not the absence of force.

When friction is removed, a body continues moving uniformly. Thus Aristotle's conclusion was incorrect because he ignored friction.

---

E. Assertion and Reason Questions

1.

Assertion (A): Aristotle believed that a force is required to keep a body moving.

Reason (R): He ignored the effect of friction.

Answer: ✔ Both A and R are true and R is the correct explanation of A.

---

2.

Assertion (A): A toy car stops when the child releases the string.

Reason (R): Friction acts opposite to the direction of motion.

Answer: ✔ Both A and R are true and R correctly explains A.

---

3.

Assertion (A): Galileo imagined a frictionless world.

Reason (R): He wanted to understand the true law of motion.

Answer: ✔ Both A and R are true and R correctly explains A.

---

4.

Assertion (A): Force is necessary to maintain uniform motion.

Reason (R): Friction always acts on moving bodies.

Answer: ✘ Assertion is false but Reason is true.

---

F. Fill in the Blanks

1.

Aristotle was a ______ philosopher.

Answer: Greek

---

2.

According to Aristotle, a body requires ______ force to keep moving.

Answer: external

---

3.

The force that opposes motion is called ______.

Answer: friction

---

4.

Galileo imagined motion without ______.

Answer: friction

---

5.

Motion in fluids is opposed by ______ force.

Answer: viscous

---

6.

Galileo's work laid the foundation of ______ mechanics.

Answer: Newtonian

---

G. True or False

1.

Aristotle correctly explained the cause of motion.

Answer: False

---

2.

Friction acts opposite to motion.

Answer: True

---

3.

Galileo ignored friction.

Answer: False

---

4.

A moving body can continue moving without force if friction is absent.

Answer: True

---

5.

Viscous force acts in fluids.

Answer: True

---

H. Statement-Based Questions

Statement I:

Aristotle believed that force is needed to maintain motion.

Statement II:

He ignored the effect of friction.

a) Both statements are true and II explains I. b) Both statements are true but II does not explain I. c) I is true, II is false. d) I is false, II is true.

Answer: (a)

---

Statement I:

Galileo imagined a frictionless world.

Statement II:

Without friction, uniform motion can continue without force.

Answer: Both statements are true and II explains I.

---

I. Match the Columns

Column A	Column B
A. Aristotle	1. Frictionless world
B. Galileo	2. Opposes motion
C. Friction	3. Force needed to keep motion
D. Viscous Force	4. Acts in fluids

Answers

A → 3

B → 1

C → 2

D → 4

---

J. Case Study Questions

Case Study

A child pulls a toy car using a string. The car moves with constant speed while the child keeps pulling. When the child releases the string, the car gradually slows down and stops.

Questions

1. Why does the toy car stop?

Answer: Due to friction between the car and the floor.

---

2. Which philosopher would say that force is required to keep the toy car moving?

Answer: Aristotle.

---

3. Which scientist corrected this idea?

Answer: Galileo.

---

4. What force opposes the motion of the toy car?

Answer: Frictional force.

---

5. What would happen if friction were absent?

Answer: The toy car would continue moving with constant velocity.

---

K. Higher Order Thinking Skills (HOTS)

1.

A hockey puck slides on a perfectly smooth ice surface. No force acts on it after it is hit. What will happen?

Answer: The puck will continue moving with constant velocity because no friction acts on it.

---

2.

Why was Aristotle's theory accepted for many centuries?

Answer: Because it matched everyday observations where moving bodies stop due to friction. The role of friction was not understood at that time.

---

Important CBSE Exam Questions

1 Mark

• Who proposed Aristotle's law of motion?
• What force opposes motion?
• Define viscous force.

2 Marks

• State Aristotle's law of motion.
• Why does a toy car stop after being released?

3 Marks

• Explain the flaw in Aristotle's argument.
• Discuss the role of friction in motion.

5 Marks

• Explain Aristotle's fallacy with examples.
• Describe Galileo's contribution in correcting Aristotle's views on motion.

Competency-Based Question

A student says, "A moving bicycle stops because no force acts on it." Is the statement correct? Give a reason.

Answer: No. The bicycle stops because friction and air resistance oppose its motion, not because force is absent. Force is required only to change motion, not to maintain uniform motion.

ARISTOTLE'S FALLACY

│

├── Main Question

│   │

│   └── Is force required to keep a body moving?

│

├── Historical Importance

│   │

│   ├── Answer took centuries

│   ├── Correct answer given by Galileo

│   ├── Foundation of Newtonian Mechanics

│   └── Beginning of Modern Science

│

├── Aristotle's View

│   │

│   ├── Greek Philosopher (384 BC – 322 BC)

│   ├── Studied motion of bodies

│   └── Believed:

│       "Continuous force is needed to keep a body moving"

│

├── Aristotle's Example

│   │

│   └── Arrow shot from a bow

│       │

│       └── Air behind arrow keeps pushing it forward

│

├── Aristotle's Law of Motion

│   │

│   └── External force is required

│       to keep a body in motion

│

├── Why Aristotle's Idea Seemed Correct

│   │

│   ├── Based on everyday observations

│   ├── Moving objects eventually stop

│   ├── Bicycle stops when pedalling stops

│   ├── Ball stops rolling

│   └── Toy car comes to rest

│

├── Toy Car Example

│   │

│   ├── Child pulls toy car with string

│   ├── Car moves while pulling

│   ├── Child releases string

│   └── Car eventually stops

│

├── Aristotle's Mistake

│   │

│   └── Ignored friction

│

├── Friction

│   │

│   ├── Opposes motion

│   ├── Acts opposite to velocity

│   ├── Slows moving bodies

│   └── Causes objects to stop

│

├── During Uniform Motion

│   │

│   ├── Child's Pulling Force →

│   ├── Frictional Force ←

│   ├── Both are equal

│   └── Net Force = 0

│

├── If Friction Were Absent

│   │

│   ├── No opposing force

│   ├── No continuous pulling required

│   ├── Body keeps moving

│   └── Uniform motion continues

│

├── Opposing Forces in Nature

│   │

│   ├── Solids

│   │   └── Friction

│   │

│   └── Fluids

│       └── Viscous Force (Drag)

│

├── Galileo's Contribution

│   │

│   ├── Imagined a frictionless world

│   ├── Analyzed ideal motion

│   └── Reached correct conclusion

│

├── Galileo's Conclusion

│   │

│   └── Force is not needed

│       to maintain uniform motion

│

├── Foundation For

│   │

│   ├── Law of Inertia

│   ├── Newton's First Law

│   └── Newtonian Mechanics

│

└── Exam Corner

    │

    ├── Aristotle:

    │   Force needed to keep motion

    │

    ├── Galileo:

    │   Force needed only to change motion

    │

    ├── Real Reason Objects Stop:

    │   Friction

    │

    └── Without Friction:

        Uniform motion continues forever

INTERNAL LINKS

Laws of Motion Introduction Notes

Law of Inertia Explained

Newton's First Law of Motion

Newton's Second Law of Motion

Newton's Third Law of Motion

Friction Class 11 Physics Notes

Motion in a Straight Line Notes

Uniform and Non-Uniform Motion

Galileo's Contributions to Physics

Conservation of Momentum Notes

Circular Motion Notes

CBSE Class 11 Physics Important Questions

NEET Physics Chapter-wise MCQs

NCERT Solutions for Laws of Motion

Physics Assertion and Reason Questions Collection

Laws of Motion Introduction Class 11 Physics Notes CBSE & NEET

 

Chapter 4: Laws of Motion – Introduction (NEET Level Easy Notes) 

- Dr.Sanjaykumar pawar

1. What was studied in the previous chapter?

• In the previous chapter, we studied motion of particles.
• We learned how to describe motion using:
  • Velocity → tells how fast and in which direction an object moves.
  • Acceleration → tells how velocity changes with time.
• We could describe motion mathematically.
• But one important question remained:

Question:

What causes a body to move or change its motion?

This question is answered in the chapter Laws of Motion.

---

2. Need for Force in Daily Life

• From our everyday experience, we observe that an object at rest does not start moving on its own.
• Some external action is needed.

Examples:

• A football starts moving only when someone kicks it.
• A stone moves upward only when someone throws it.
• Tree branches swing because of wind.
• A boat moves because of the flowing river.

Conclusion:

➡️ To move an object from rest, an external force is required.

---

3. Force Can Also Stop Motion

• Force is not only used to start motion.
• It can also slow down or stop a moving object.

Example:

• A ball rolling down a slope can be stopped by applying force in the opposite direction.

Conclusion:

➡️ Force can:

1. Start motion.
2. Stop motion.
3. Change speed.
4. Change direction.

---

4. Contact Forces

• In many cases, force is applied through physical contact.

Examples:

• Hand kicking a football.
• Hand throwing a stone.
• Wind pushing tree branches.
• Water pushing a boat.

Definition:

Contact Force: A force that acts when two objects touch each other.

Examples:

• Muscular force
• Friction force
• Normal reaction force

---

5. Non-Contact Forces

• Force can also act without physical contact.

Example 1: Gravitational Force

• A stone dropped from a building falls toward Earth.
• Earth attracts the stone due to gravity.

Example 2: Magnetic Force

• A magnet attracts an iron nail from a distance.

Conclusion:

➡️ Physical contact is not always necessary for force to act.

Definition:

Non-Contact Force: A force that acts without direct contact.

Examples:

• Gravitational force
• Magnetic force
• Electrostatic force

---

6. Important Definition of Force

Force

A force is a push or pull that can:

• Start motion,
• Stop motion,
• Change speed,
• Change direction,
• Change shape of an object.

SI Unit:

Newton (N)

---

7. External Agency

• The source that applies force is called an external agency.

Examples:

External Agency	Force Produced
Hand	Muscular force
Wind	Air force
Flowing water	Water force
Earth	Gravitational force
Magnet	Magnetic force

Key Point:

• An external agency may be:
  • In contact with the object.
  • Away from the object.

---

8. Important Question Raised in the Chapter

Consider a skater moving on a smooth ice surface with constant speed.

Question:

Does he need a continuous force to keep moving?

At first glance, the answer seems "Yes."

But this idea is actually incorrect.

This misconception was given by Aristotle, and later corrected by Galileo and Newton.

This leads to:

• Aristotle's Fallacy
• Law of Inertia
• Newton's First Law of Motion

which are discussed in the next sections.

---

NEET Quick Facts

Force is needed to:

✅ Start motion

✅ Stop motion

✅ Change speed

✅ Change direction

✅ Change shape

---

Types of Forces

1. Contact Forces

• Muscular force
• Friction
• Normal force

2. Non-Contact Forces

• Gravitational force
• Magnetic force
• Electrostatic force

---

Most Important NEET Concept

A force is required to change the state of motion, but not necessarily to maintain uniform motion.

This idea forms the basis of Newton's First Law of Motion (Law of Inertia).

---

One-Line Revision

• Velocity describes motion.
• Acceleration describes change in motion.
• Force explains why motion changes.
• Force can start, stop, speed up, slow down, or change direction.
• Force may be contact or non-contact.
• Earth attracts objects through gravity.
• Magnets attract iron without contact.
• The major question of this chapter is: "Is force required to keep a body moving uniformly?"
• The answer leads to Newton's Laws of Motion. ✅  

Class 11 Physics Laws of Motion Introduction – Easy Notes, MCQs, and Exam Questions for CBSE and NEET Preparation.

Class 11 Physics – Laws of Motion (Introduction) Question Bank with Answers

(CBSE + NEET Foundation Level)

---

A. Multiple Choice Questions (MCQs)

1. Which quantity is sufficient to describe uniform motion?

a) Acceleration b) Velocity c) Force d) Momentum

Answer: (b) Velocity

---

2. Which quantity is additionally required to describe non-uniform motion?

a) Mass b) Velocity c) Acceleration d) Density

Answer: (c) Acceleration

---

3. A football at rest starts moving when:

a) Gravity acts b) It is kicked c) Air acts d) It moves itself

Answer: (b) It is kicked

---

4. Which of the following is a non-contact force?

a) Friction b) Muscular force c) Magnetic force d) Tension

Answer: (c) Magnetic force

---

5. A stone falls toward Earth due to:

a) Friction b) Magnetic force c) Gravitational force d) Tension

Answer: (c) Gravitational force

---

6. The SI unit of force is:

a) Joule b) Newton c) Watt d) Pascal

Answer: (b) Newton

---

7. Which of the following is a contact force?

a) Gravity b) Magnetism c) Friction d) Electrostatic force

Answer: (c) Friction

---

8. Force can change:

a) Speed b) Direction c) State of motion d) All of these

Answer: (d) All of these

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B. Very Short Answer Questions (1 Mark)

1. What is force?

Answer: Force is a push or pull that can change the state of motion of a body.

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2. Name one contact force.

Answer: Frictional force.

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3. Name one non-contact force.

Answer: Gravitational force.

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4. What is the SI unit of force?

Answer: Newton (N).

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5. Give one example of gravitational force.

Answer: A stone falling toward Earth.

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6. Give one example of magnetic force.

Answer: A magnet attracting an iron nail.

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C. Short Answer Questions (2–3 Marks)

1. Why is force required to move a stationary object?

Answer: A stationary object remains at rest unless an external force acts on it. Force changes the state of rest and starts motion.

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2. Differentiate between contact and non-contact forces.

Contact Force	Non-Contact Force
Requires physical contact	Does not require contact
Example: Friction	Example: Gravity

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3. Give three examples where force starts motion.

Answer:

1. Kicking a football.
2. Throwing a stone.
3. Wind moving tree branches.

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4. Give two examples where force acts from a distance.

Answer:

1. Earth attracting a stone.
2. Magnet attracting an iron nail.

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D. Long Answer Questions (5 Marks)

1. Explain the need for force with suitable examples.

Answer:

Force is a push or pull that changes the state of motion of a body.

Force is required to:

1. Start motion

   • Example: Kicking a football.

2. Stop motion

   • Example: Stopping a rolling ball.

3. Change speed

   • Example: Accelerating a bicycle.

4. Change direction

   • Example: Hitting a moving cricket ball.

Force may act through contact or from a distance. Examples include gravitational and magnetic forces.

Thus, force is responsible for changing the state of motion of objects.

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2. Explain contact and non-contact forces with examples.

Answer:

Contact Forces

These forces act only when objects are in physical contact.

Examples:

• Friction
• Muscular force
• Tension

Non-Contact Forces

These forces act without physical contact.

Examples:

• Gravitational force
• Magnetic force
• Electrostatic force

Thus, forces can act both through contact and at a distance.

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E. Assertion and Reason Questions

1.

Assertion (A): A magnet can attract an iron nail from a distance.

Reason (R): Magnetic force is a non-contact force.

Answer: ✔ Both A and R are true and R is the correct explanation of A.

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2.

Assertion (A): A football at rest starts moving when kicked.

Reason (R): Force changes the state of motion.

Answer: ✔ Both A and R are true and R correctly explains A.

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3.

Assertion (A): A falling stone accelerates toward Earth.

Reason (R): Earth exerts gravitational force on the stone.

Answer: ✔ Both A and R are true and R correctly explains A.

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F. Fill in the Blanks

1.

A ______ is needed to change the state of motion of a body.

Answer: force

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2.

A force acting without contact is called a ______ force.

Answer: non-contact

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3.

The SI unit of force is ______.

Answer: Newton

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4.

A magnet attracts an iron nail due to ______ force.

Answer: magnetic

---

5.

A stone falls toward Earth due to ______ force.

Answer: gravitational

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G. True/False Questions

1.

Force is required to change the state of motion.

Answer: True

---

2.

Gravitational force is a contact force.

Answer: False

---

3.

A magnet can attract iron without touching it.

Answer: True

---

4.

Velocity alone describes non-uniform motion.

Answer: False

---

5.

Wind can exert force on tree branches.

Answer: True

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H. Statement-Based Questions

Statement I:

A force can act without physical contact.

Statement II:

Gravity and magnetic force are examples of non-contact forces.

a) Both statements are true. b) Both statements are false. c) Statement I is true but II is false. d) Statement I is false but II is true.

Answer: (a) Both statements are true.

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Statement I:

Force is needed to stop a moving object.

Statement II:

Force cannot change speed.

Answer: Statement I is true but Statement II is false.

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I. Match the Columns

Column A	Column B
A. Gravity	1. Contact force
B. Friction	2. Iron nail attraction
C. Magnet	3. Earth pulls stone
D. Hand push	4. Muscular force

Answers

A → 3

B → 1

C → 2

D → 4

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J. Case Study Questions

Case Study

A student drops a stone from the roof of a building. The stone starts moving downward and gains speed. Nearby, a magnet attracts an iron nail placed on a table.

Questions

1. Why does the stone fall?

Answer: Due to gravitational force.

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2. Is gravity a contact force?

Answer: No, it is a non-contact force.

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3. Why does the nail move toward the magnet?

Answer: Due to magnetic force.

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4. What type of force is magnetic force?

Answer: Non-contact force.

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5. Name two non-contact forces involved in this case.

Answer:

1. Gravitational force
2. Magnetic force

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Important CBSE Exam Questions

1 Mark

• Define force.
• State SI unit of force.
• Give one example of non-contact force.

2 Marks

• Differentiate between contact and non-contact forces.
• Explain why force is required to stop a moving body.

3 Marks

• Explain three effects of force.
• Give examples of contact and non-contact forces.

5 Marks

• Explain the need for force in daily life with examples.
• Discuss contact and non-contact forces with suitable examples.

HOTS Question

A skater moves on a smooth ice surface with constant speed. Is force necessary to keep him moving? Explain.

Answer: No. A force is required only to change the state of motion. Uniform motion can continue without an external force if no opposing force acts.

LAWS OF MOTION (Introduction)

│

├── Previous Chapter

│   │

│   ├── Motion of Particle

│   ├── Velocity

│   │   └── Describes uniform motion

│   └── Acceleration

│       └── Describes non-uniform motion

│

├── Main Question

│   │

│   └── What governs the motion of bodies?

│

├── Force

│   │

│   ├── Push or Pull

│   ├── Causes motion

│   ├── Stops motion

│   ├── Changes speed

│   ├── Changes direction

│   └── Changes state of motion

│

├── Force Needed to Start Motion

│   │

│   ├── Kick a football

│   ├── Throw a stone upward

│   ├── Wind moves branches

│   └── River flow moves boat

│

├── Force Needed to Stop Motion

│   │

│   └── Stop a rolling ball by applying force opposite to motion

│

├── External Agency

│   │

│   ├── Hand

│   ├── Wind

│   ├── Flowing water

│   ├── Earth

│   └── Magnet

│

├── Types of Force

│   │

│   ├── Contact Force

│   │   │

│   │   ├── Hand pushing object

│   │   ├── Wind on branches

│   │   └── Water on boat

│   │

│   └── Non-Contact Force

│       │

│       ├── Gravitational Force

│       │   └── Stone falls toward Earth

│       │

│       └── Magnetic Force

│           └── Magnet attracts iron nail

│

├── Important Conclusion

│   │

│   ├── Force may act through contact

│   └── Force may act from a distance

│

└── Key Question of Chapter

    │

    ├── Is force required to keep a body moving uniformly?

    │

    ├── Example:

    │   └── Skater moving with constant speed on ice

    │

    └── Leads To

        │

        ├── Aristotle's Fallacy

        ├── Law of Inertia

        ├── Newton's First Law

        ├── Newton's Second Law

        ├── Newton's Third Law

        └── Conservation of Momentum

INTERNAL LINKS

Motion in a Straight Line Class 11 Notes

Units and Measurements Notes

Vectors and Scalars Explained

Laws of Motion Complete Chapter Notes

Newton's First Law of Motion

Newton's Second Law of Motion

Newton's Third Law of Motion

Conservation of Momentum Notes

Friction Complete Notes

Circular Motion Class 11 Physics

Class 11 Physics MCQ Collection

NEET Physics Important Questions

CBSE Class 11 Physics Previous Year Questions

Work Energy and Power Notes

Mechanical Properties of Solids Notes