Newton’s Laws of Motion
Complete notes by home academy
Introduction
The laws of motion formulated by Isaac Newton are among the most important principles of physics. These laws explain how objects move and how forces affect motion. Newton published these laws in his famous book Philosophiæ Naturalis Principia Mathematica in 1687.
Newton’s Laws of Motion form the foundation of classical mechanics and are widely used in engineering, transportation, sports, space science, and everyday life.
What is Motion?
Motion is the change in position of an object with time.
Examples
A moving car
Flying airplaneRolling football
Rotating fan
Motion occurs due to the action of force.
What is Force?
Force is a push or pull that changes or tries to change the state of rest or motion of an object.
Formula of Force
F = ma
Where:
F = Force
m = Massa = Acceleration
Newton’s First Law of Motion
Statement
“An object remains at rest or continues to move with uniform velocity in a straight line unless acted upon by an external unbalanced force.”
This law is also called the Law of Inertia.
Explanation
Objects naturally resist changes in their state of motion.
A stationary object remains stationary.
A moving object continues moving at constant speed unless an external force acts.Examples of First Law
1. Passenger Falls Backward
When a bus suddenly starts, passengers fall backward because their body tends to remain at rest.
2. Dust from Carpet
Dust particles come out when a carpet is beaten due to inertia of rest.
3. Seat Belts in Cars
Seat belts prevent passengers from moving forward suddenly during braking.
Inertia
Inertia is the property of matter by which it resists change in its state of motion.
Types of Inertia
| Type | Example |
|---|---|
| Inertia of Rest | Passenger falls backward |
| Inertia of Motion | Passenger falls forward |
| Inertia of Direction | Stone moving in circular path |
Newton’s Second Law of Motion
Statement
“The rate of change of momentum of an object is directly proportional to the applied force and takes place in the direction of force.”
Mathematical Form
F = ma
Where:
Force increases acceleration.
Greater mass requires greater force.Momentum
Momentum is the quantity of motion possessed by an object.
Formula
genui{"math_block_widget_always_prefetch_v2":{"content":"p = mv"}}
Where:
p = Momentum
m = Massv = Velocity
Examples of Second Law
1. Kicking a Football
A stronger kick produces greater acceleration.
2. Empty vs Loaded Truck
A loaded truck requires more force to move than an empty truck.
3. Rocket Launch
Huge force is needed to launch rockets into space.
Newton’s Third Law of Motion
Statement
“For every action, there is an equal and opposite reaction.”
Explanation
Forces always occur in pairs:
Action force
Reaction forceBoth forces are equal in magnitude but opposite in direction.
Examples of Third Law
1. Recoil of Gun
Bullet moves forward while gun moves backward.
2. Walking
We push the ground backward, and the ground pushes us forward.
3. Rocket Propulsion
Hot gases move downward and rocket moves upward.
Applications of Newton’s Laws
| Field | Application |
|---|---|
| Transportation | Seat belts, brakes |
| Sports | Cricket, football, hockey |
| Space Science | Rocket launching |
| Engineering | Machine design |
| Daily Life | Walking, lifting objects |
Important Differences
Balanced vs Unbalanced Force
| Balanced Force | Unbalanced Force |
|---|---|
| Net force = 0 | Net force ≠ 0 |
| No acceleration | Produces acceleration |
| Motion unchanged | Motion changes |
Importance of Newton’s Laws
Explain motion of bodies
Basis of mechanicsUsed in engineering and technology
Essential for competitive examinations
Helpful in understanding real-life phenomena
Important Points for Exams
First law = Law of inertia
Second law gives relation between force and accelerationThird law explains action-reaction principle
Force is a vector quantity
SI unit of force = Newton
Momentum depends on mass and velocity
Larger mass requires larger force
Frequently Asked Questions (FAQs)
Q1. Who discovered the laws of motion?
The laws of motion were discovered by Isaac Newton.
Q2. Why is Newton’s first law called the law of inertia?
Because it explains the tendency of objects to resist changes in their state of motion.
Q3. What is inertia?
Inertia is the property of matter to resist change in motion or rest.
Q4. What is the SI unit of force?
The SI unit of force is Newton (N).
Q5. Which law explains rocket propulsion?
Newton’s third law of motion explains rocket propulsion.
Q6. What is momentum?
Momentum is the product of mass and velocity.
Q7. Why does a passenger fall forward when a bus stops suddenly?
Due to inertia of motion.
Q8. Which Newton’s law is used in seat belts?
Newton’s first law of motion.
Q9. Why is it easier to push an empty cart than a loaded cart?
Because the loaded cart has greater mass and requires more force.
Q10. What is meant by action and reaction?
When one body exerts force on another body, the second body exerts an equal and opposite force back.
Frequently Asked MCQs
1. Newton’s first law is also known as:
A. Law of gravitation
B. Law of momentum
C. Law of inertia
D. Law of acceleration
✅ Answer: C
2. Which law explains F = ma?
A. First law
B. Second law
C. Third law
D. Law of gravitation
✅ Answer: B
3. Rocket propulsion works on:
A. First law
B. Second law
C. Third law
D. Universal gravitation
✅ Answer: C
4. Momentum depends on:
A. Mass only
B. Velocity only
C. Mass and velocity
D. Weight only
✅ Answer: C
5. SI unit of force is:
A. Joule
B. Watt
C. Newton
D. Pascal
✅ Answer: C
Statement-Based Questions
Question 1
Consider the following statements:
Newton’s first law is called the law of inertia.
Newton’s second law relates force with acceleration.
Newton’s third law explains conservation of momentum.
Choose the correct option:
A. Only 1 and 2
B. Only 2 and 3
C. Only 1 and 3
D. 1, 2 and 3
✅ Answer: D
Question 2
Which of the following statements are correct?
Force is a vector quantity.
Momentum depends upon mass and velocity.
Balanced force produces acceleration.
A. Only 1 and 2
B. Only 2 and 3
C. Only 1 and 3
D. 1, 2 and 3
✅ Answer: A
Conclusion
Newton’s Laws of Motion are fundamental principles that explain the behavior of moving objects under the influence of force. These laws are essential for understanding mechanics, engineering, transportation, sports, and space science. Questions from Newton’s laws are frequently asked in SSC, JKSSB, Railway, NEET, UPSC, and other competitive examinations.
Prepared By Home Academy