Physics Chapter - Laws of Motion

                                               LAWS OF MOTION 

What is Laws of motion

Laws of motion are the laws given by Newton regarding the motion of objects. You are already familiar with the 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. For example, you know that if you apply the same force on an elephant and on football as shown in the below figure then the football will move more quickly than the elephant.

  Laws of Motion Physics - Newton's second Law

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.

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

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 exam. 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 life as well as studying physics.


Notes on Laws of motion-

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

Then we will understand important formulas from this chapter. Remembering these formulas will increase your speed while question-solving.

  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.

 Laws of motion Overview

In this chapter, we will learn about the various force and laws of motion. As you know that if you have to move stationary body you will have to apply force, similarly if you have to stop a moving body then also you have to apply force. This is nothing but Newton's 1st law which you will learn in this chapter and which says every object will remain at rest or in uniform motion until we don't apply any external force to change its state. And very important and interesting law which is third laws of motion which states that for every action (force) in nature there is an equal and opposite reaction. We see various examples and application of Newton's laws of motion in our ur day to day activities. Walking, Bouncing Of Ball, Rocket Propulsion all have 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 example and Impulse, friction and its types, etc. In this chapter, you will deal with forces like  Weight, Reaction or Normal Force, Tension, Spring force, etc. You will also be able to add these forces with the help of various force vector addition laws like 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.

 

  Laws of motion Formulas

  • For equilibrium,

 \sum \vec{F_{net}}= 0   

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

  • Lami’s theorem-

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

Laws of Motion- Formula

 

  • Spring force-

F= -Kx

  • Newton's 2nd Law

F=ma

  • Newton's 3rd Law

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

  • Linear Momentum

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

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

  • Impulse-Momentum Theorem-

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

  • Centripetal Force= F=m\omega ^2r

  • Kinetic friction force =f_{K}=\mu_{K} R

  • Limiting Friction force= f_{l}=\mu_{s}R


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