Newton's Laws of Motion

Edited By Vishal kumar | Updated on Sep 16, 2024 02:58 PM IST

This article discusses Sir Isaac Newton's Laws of Motion, which have long revolutionized our knowledge of the physical world, and, hundreds of years ago, explains Newton's three laws, which present a better understanding of their meaning. First, the paper shall look at Newton's First Law of Motion, called the Law of Inertia: how objects act when they are in rest or uniform motion. Now coming to Newton's Second Law of Motion, we will get to know how the motion of an object changes when force is applied to it. In Newton's Third Law of Motion, we will see how the forces exerted on each other by two objects are always equal in magnitude and opposite in direction. A brief about Newton's laws with summarized important terminologies and numerals based on the Laws of Motion provided with some live examples. In fact, our FAQs have some other questions too, such that after reading this whole set of information, the students would have a perfect understanding of Newton's Laws of Motion.

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This Story also Contains

Newton's Laws of Motion
Notes on Newton's Laws of Motion
Newton's Laws of Motion Topics
Newton's Laws of Motion Overview
Newton's Laws of Motion Formulas
How to prepare Newton's Laws of Motion
How to Solve Newton's Laws of Motion questions.
Newton's Laws of Motion Tips
Newton's Laws of Motion Books
Summary

Laws of motion are the three fundamental principles given by Sir Issac Newton (1642–1727) regarding the motion of objects which form the basis of Mechanics. He presented these principles to the world in his book Philosophiae Naturalis Principia Mathematica (The Mathematical Principles of Natural Philosophy), which was published in 5 July 1687. You are already familiar with Newton's laws of motion as you apply or observe these laws on a daily basis in various daily activities. This chapter helps you to understand these laws in mathematical forms with some suitable examples

Example 1: A passenger is standing freely in a moving bus. When the bus stops suddenly. The passenger falls forward due to the inertia of motion. This is an example of Newton’s first law of motion,

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Example 2: if you apply the same force on an elephant and on a football as shown in the below figure then the football will move more quickly than the elephant.

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This is nothing but Newton's 2nd law which mathematically says

F = ma where F = Force on the body, m = mass of the body and a = acceleration of the body.

The mass of a football is less than that of an elephant hence for the same force football will have more acceleration, and will move quickly.

Example 3: A box lying on a table exerts a force on the table which is equal to the weight of the box. This is the force of action. The table supports the box by exerting an equal force on the box. This is the force of reaction. As the system is at rest, the net force on it is zero. Therefore force of action and reaction must be equal and opposite. This is an application of Newton's third law.

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Newton's Laws of Motion is a very basic and important chapter from the mechanics part of physics. It is very important to master the concepts from this chapter at an early stage as this forms the basis of your preparation for all competitive exams. This chapter is very important because it will test your knowledge of the chapter Kinematics, and it will be also useful and crucial for you for solving questions from the next chapters namely Work Energy and Power, Rotational Motion and to some extent gravitation. This chapter will also tell you how important these laws are in our daily lives as well as studying physics.

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Notes on Newton's Laws of Motion

So we will discuss step by step the important topics from this chapter followed by an overview of this chapter.

Then we will look into the important formulas from this chapter. Memorizing these formulas will improve your speed while solving questions.

Newton's Laws of Motion Topics

Force and Inertia
Newton's Law of motion- Newton's First Law, Newton's Second Law, Newton's Third Law
Momentum, Impulse
Law of conservation of linear momentum and applications of linear momentum
Equilibrium of concurrent forces
Kinetic and Static friction, laws of friction, rolling friction
Dynamics of uniform circular motion, Centripetal force, and applications of Centripetal force.

Newton's Laws of Motion Overview

In this chapter, we will learn about various forces and laws of motion. As you know if you have to move a stationary body a force should be applied. Similarly, if you have to stop a moving body you also have to apply force. This is nothing but Newton's 1st law which you will learn in this chapter and which says that a body continues to be in the state of rest or of uniform motion along a straight line unless compelled by an external force to change its state. Acceleration of a rocket due to thrust is an example of Newton’s second law of motion which states that the rate of change of linear momentum of a body is directly proportional to the external force applied on the body, and this change always takes place in the direction of the applied force. The most important and interesting law which is the third law of motion states that for every action (force) in nature, there is an equal and opposite reaction. We see various examples and applications of Newton's laws of motion in our day-to-day activities. Walking, Bouncing of Ball, and Rocket Propulsion are all an application of Newton's third law. In this chapter, you will also learn about Inertia and its type, Momentum, Force and its types with examples and Impulse, friction and its types, etc. In this chapter, you will deal with forces like Weight, Reaction or Normal Force, Tension, Spring force and more. You will also be able to add these forces with the help of various force vector addition laws like the parallelogram law of force and polygon law of forces to get resultant forces. You will learn about friction which is nothing but an Opposing Force which is parallel to the surface and opposite to the direction of Relative Motion.

Newton's Laws of Motion Formulas

First law equation for equilibrium,

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when a particle is in equilibrium, the total of the forces acting on it is zero

$\sum \vec{F_{net}}= 0$

or,

$\sum \vec{F_{x}}= 0,\sum \vec F_{y}= 0, \sum \vec F_{z}= 0$

Lami’s theorem-

If a particle in equilibrium is subjected to only three coplanar, concurrent and non-collinear forces, the vectors representing the three forces have a specific geometry which is described by Lami’s theorem.

$\frac{F_{1}}{sin\alpha }=\frac{F_{2}}{sin\beta }=\frac{F_{3}}{sin\gamma }$

Laws of Motion- Formula

Spring force-

The restoring force exerted by the spring when it is stretched to come back to its original position.

Newton's 2nd Law

The force acting on an object is equal to the object’s mass multiplied by its acceleration.

Newton's 3rd Law

To every action, there is an equal(in magnitude) and opposite(in direction) reaction.

$\vec{F_{AB}}=-\vec{F_{BA}}$

Linear Momentum

A vector quantity which is the product of an object’s mass and velocity.

$\overrightarrow{P}=M\times\vec V$

Impulse

When a large force acts on a body for a very small time interval,it is called impulsive force.

$\vec{I}=\int_{t_{1}}^{t_{2}}\vec{F}\cdot dt$

Impulse-Momentum Theorem-

The impulse applied to an object is equal to its change in momentum

$\int_{t_{1}}^{t_{2}}\vec{F}dt=\int_{p_{1}}^{p_{2}}\vec{dp}$

Centripetal Force

The force that keeps an object moving in a curved path by pulling it towards the centre of the circle.

$F=m\omega ^2r$

Kinetic friction force

The friction opposing the increased applied force that further sets the body in motion.

$f_{K}=\mu_{K} R$

Limiting Friction force

The maximum value of static friction when the body is at the verge of moving over the other while increasing the applied force $f_{l}=\mu_{s}R$

NCERT Notes Subject Wise Link:

How to prepare Newton's Laws of Motion

First, you should have a good command over the concepts of Newton's Laws of motion and you should also know how to apply them well at the time of the entrance exam or while solving questions. Please try to understand each concept from this chapter, with the help of theory, solved questions and video lectures on each important concept. For each concept practice enough problems so that you have a thorough understanding of the concept. Solve all the questions with proper concentration and try to do all calculations by yourself without checking the solution first.

How to Solve Newton's Laws of Motion questions.

Choose a convenient system.
Draw a diagram which schematically shows the various parts of a system.
Draw the free-body diagram of each part of the system.
In a free-body diagram, you must include information about forces (their magnitudes and directions).
The rest should be treated as unknowns or to be determined using laws of motion.
Apply Newton's third law wherever necessary.

If a system is in equilibrium or all the forces working on a body are Concurrent Forces then the calculations of the question would be easy. Need a clear understanding of the concept of solving problems related to the Recoiling of Guns, Firing of Bullet, and Rocket Propulsion. The answer sheet should have neat and clean calculations to avoid negative markings. Question-related friction gets more and more complicated when we involve more blocks in contact, inclined planes, pulleys, etc, variable external force, etc. But you can solve these questions with ease with a proper study plan.

Newton's Laws of Motion Tips

This chapter is the basics of mechanics which is important for further studies, hence practice is the key here for getting a good hold on this chapter.
Questions to draw FBD are repetitive so draw clear FBD and then solve the questions. This will increase your accuracy.
Make a plan to prepare for this chapter and Stick to a Timetable.
Study the concept first and then start solving numerical questions. Don't go through questions directly without knowing the concept.
Solve previous year questions of various exams from this chapter.
Use smart methods to solve questions.

As said by Matshona Dhliwayo

“Work hard, and you will earn good rewards.

Work smart, and you will earn great rewards.

Work hard and work smart, and you will earn extraordinary rewards"

Newton's Laws of Motion Books

For Newton's Laws of Motion, chapter concepts in NCERT are enough but you have to practice different types of questions including previous year's questions and also attend online mock tests.

The standard books available for competitive exam preparation:

‘Concepts of Physics’ (Vol. 1 and Vol. 2) by H.C. Verma
‘Understanding Physics’ by D. C. Pandey (Arihant Publications).
‘Comprehensive Physics for Class 12’ by J.P Sharma

Summary

Together, Newton's laws of motion form the foundation of physics.

Under the first law of motion, typically referred to as the law of inertia, an object will sit still or move in some direction with constant velocity unless disturbed by an external force.
The second law then relates this force on the object to its resulting change in motion. It does so with the rule that force is mass times acceleration; that is, F = ma.
The third is the law of equal and opposite reaction for everything that happens. All three could be said to provide a frame of reference for how things move and interact with each other in the universe. From classical mechanics all the way up to astrophysics, they think of all motions on both the large and small scales.

NCERT Solutions Subject-wise link:

NCERT Exemplar Solutions Subject-wise link: