3.1 Introduction

Introduction

Motion is the change in the position of an object with time. How does the position change with time? To describe motion, we developed the concepts of velocity and acceleration. The study of the motion of objects along a straight line, is 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.

Motion in a straight line is nothing but linear motion. As the name suggests, it’s in a particular straight line, thus it can be said that it uses only one dimension. The linear motion, also called the Rectilinear Motion can be of two types:

1. Uniform linear motion with constant velocity or zero acceleration
2. Non-Uniform linear motion with variable velocity or non-zero acceleration

Uniform Motion in a Straight Line

If a body travels in a straight line and covers an equal amount of distance in an equal interval of time, it is said to have uniform motion. In simple words, a body is said to have uniform acceleration if the rate of change of its velocity remains constant.

Example: If a car travels at a speed of 120 km/hour, it will cover 2 km/minute. In this sense, the motion of car acceleration is uniform.

Non-uniform Motion in a Straight Line

Unlike the uniform acceleration, the body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time, that is the rate of change of its velocity changes at different points of time during its movement.

Example: A boy is kicking a football. It might cover 3 meters in the first attempt, 8 meters in the second change, 10 meters in the third attempt, and so on as per the velocity exerted by the boy.