NCERT Book Class 11 Physics Chapter 2 Motion in a Straight Line

CHAPTER TWO

MOTION IN A STRAIGHT LINE

2.1 INTRODUCTION
Motion is common to everything in the universe. We walk,
run and ride a bicycle. Even when we are sleeping, air moves
2.1 Introduction into and out of our lungs and blood flows in arteries and
2.2 Instantaneous velocity and veins. We see leaves falling from trees and water flowing
speed down a dam. Automobiles and planes carry people from one
2.3 Acceleration place to the other. The earth rotates once every twenty-four
2.4 Kinematic equations for hours and revolves round the sun once in a year. The Sun
uniformly accelerated motion itself is in motion in the Milky Way, which is again moving
2.5 Relative velocity within its local group of galaxies.
Summary
Motion is change in position of an object with time. How
Points to ponder does the position change with time ? In this chapter, we shall
Exercises learn how to describe motion. For this, we develop the
concepts of velocity and acceleration. We shall confine
ourselves to the study of motion of objects along a straight
line, also known as rectilinear motion. For the case of
rectilinear motion with uniform acceleration, a set of simple
equations can be obtained. Finally, to understand the relative
nature of motion, we introduce the concept of relative velocity.
In our discussions, we shall treat the objects in motion as
point objects. This approximation is valid so far as the size
of the object is much smaller than the distance it moves in a
reasonable duration of time. In a good number of situations
in real-life, the size of objects can be neglected and they can
be considered as point-like objects without much error.
In Kinematics, we study ways to describe motion without
going into the causes of motion. What causes motion
described in this chapter and the next chapter forms the
subject matter of Chapter 4.