Motion In A Straight Line: Class 11 Physics NCERT Chapter 3

Key Features Of NCERT Material for Class 11 Science Chapter 3 –  Motion In A Straight Line

In the last chapter 2, you learned about Units and Measurements in Physics. In this chapter, you will learn about Motion in a Straight Line.

Quick revision notes

  • Introduction

Motion is one of the critical themes in material science. Everything known to mankind moves. It may just be a modest quantity of development and incredibly moderate, however development occurs. Regardless of whether you have all the earmarks of being stopping, the Earth is moving around the sun, and the sun is moving around our cosmic system. “An article is supposed to be moving if its position changes with time”. The idea of movement is a re’ live one and a body that might be moving comparative with one reference framework, might be very still comparative with another. 

There are two branches in material science that look at the movement of an article. 

(I) Kinematics: It depicts the movement of articles, without taking a gander at the reason for the movement. 

(ii) Dynamics: It relates the movement of items to the powers which cause them. 

  • Point Object 

In the event that the length secured by the articles are extremely huge in contrast with the size of the items, the items are viewed as point objects. 

  • Reference Systems 

The movement of a molecule is constantly portrayed as for a reference framework. A reference framework is made by accepting a subjective point as source and envisioning a co-ordinate framework to be connected to it. This co-ordinate framework picked for a given issue establishes the reference framework for it. We by and large pick a co-ordinate framework joined to the earth as the reference framework for the greater part of the issues. 

  • Total Path Length (Distance) 

For a molecule moving the absolute length of the real way crossed among starting and last places of the molecule is known as the ‘complete way length’ or separation secured by it. 

  • Types of Motion 

So as to totally portray the movement of an item, we have to indicate its position. For this, we have to know the position co-ordinates. Sometimes, three position co-ordinates are required, while now and again two or one position co-ordinate is required. 

In light of these, movement can be delegated: 

(I) One dimensional movement. A molecule moving along a straight-line or a way is said to go through one dimensional movement. For instance, movement of a train along a straight line, uninhibitedly falling body under gravity and so forth. 

(ii) Two dimensional movement. A molecule moving in a plane is said to go through two dimensional movement. For instance, movement of a shell shot by a firearm, carrom board coins and so forth. 

(iii) Three dimensional movement. A molecule moving in space is said to go through three dimensional movement. For instance, movement of a kite in sky, movement of plane and so on. 

  • Displacement 

Uprooting of a molecule in a given time is characterized as the adjustment in the situation of molecule a specific way during that time. It is given by a vector drawn from its underlying situation to its last position. 

  • Factors Distinguishing Displacement from Distance 

— > Displacement has course. Separation doesn’t have heading. 

— > The extent of removal can be both positive and negative. 

— > Distance is consistently certain. It never diminishes with time. 

— > Distance ≥ | Displacement | 

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  • Uniform Speed and Uniform Velocity

Uniform Speed. An item is said to move with uniform speed in the event that it covers equivalent separations in equivalent time periods, howsoever little these timespans might be. 

Uniform Velocity. An item is said to move with uniform speed on the off chance that it covers equivalent relocations in equivalent time frames, howsoever little these timespans might be.

  • Variable Speed and Variable Velocity

Variable Speed. An item is said to move with variable speed in the event that it covers inconsistent separations in equivalent timespans, howsoever little these time periods might be. 

Variable Velocity. An item is said to move with variable speed in the event that it covers inconsistent relocations in equivalent timespans, howsoever little these time periods might be. 

  • Average Speed and Average Velocity

Average Speed. It is the proportion of complete way length navigated and the relating time stretch

Or

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The average speed of an item is more noteworthy than or equivalent to the greatness of the normal speed over a given time stretch. 

  • Instantaneous Speed and Instantaneous Velocity

Immediate Speed. The speed of an item at a moment of time is called quick speed. 

Or

“Instantaneous speed is the limit of the average speed as the time interval becomes infinitesimally small”.

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Instantaneous velocity

The instantaneous velocity of a particle is the velocity at any instant of time or at any point of its path.

or

“Instantaneous velocity or simply velocity is defined as the limit of the average velocity as the time interval Δt becomes infinitesimally small.”

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  • Acceleration

Acceleration is the rate of change of velocity.

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  • Uniform Acceleration

On the off chance that an item goes through equivalent changes in speed in equivalent time spans it is called uniform acceleration.

  • Average and Instantaneous Acceleration

Average Accelerating. It is the change in the velocity divided by the time-interval during which the change occurs.

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Instantaneous Acceleration. It is defined as the limit of the average acceleration as the time-interval Δt goes to zero.

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  • Kinematical Graphs

The ‘dislodging time’ and the ‘speed time’ diagrams of a molecule are regularly used to give us a visual portrayal of the movement of a molecule. The ‘state’ of the diagrams relies upon the underlying ‘co-ordinates’ and the ‘nature’ of the increasing speed of the molecule (Fig.) 

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The accompanying general outcomes are consistently substantial 

(I) The slant of the dislodging time diagram at any moment gives the speed of the molecule right then and there. 

(ii) The slant of the speed time diagram at any moment gives the size of the increasing speed of the molecule right then and there. 

(iii) The zone encased by the speed time diagram, the time-hub and the two co-ordinates at ,time moments t1 to t2 gives the separation moved by the molecule in the time-stretch from t1 to t2. 

  • Equations of Motion for Uniformly Accelerated Motion 

For consistently quickened movement, some basic conditions can be inferred that relate uprooting (x), time taken (f), beginning speed (u), last speed (v) and increasing speed (a). Following condition gives a connection among last and beginning speeds v and u of an article moving with uniform quickening a: v = u + at 

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  • Suppose a body is projected vertically upward from a point A with velocity u.

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In certain issues it is helpful to accept the descending bearing as sure, in such case all the estimations descending way are considered as sure i.e., speeding up will be +g. Be that as it may, some of the time we may need to accept upward as sure and if such case quickening will be – g. 

  • Relative Velocity

Relative speed of an item A concerning another article B is the time rate at which the article A progressions its situation regarding the item B. 

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— > The overall speed of two items moving a similar way is the distinction of the rates of the articles. 

— > The general speed of two articles moving inverse way is the aggregate of the rates of the items. 

  • IMPORTANT TABLES

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