2.1 Introduction

- We see objects moving all around us.

- Motion is a change in the position of an object with time.

- We have come across the motion of a toy car when pushed along some particular direction, the motion of a cricket ball hit by a batsman for a sixer and the motion of an aeroplane from one place to another.

- The motion of objects can be divided in three categories:

(1) motion along a straight line, i.e., rectilinear motion,

(2) motion in two dimensions, i.e., motion in a plane and,

(3) motion in three dimensions, i.e., motion in space.

- The above cited examples correspond to three types of motions, respectively.

- You have studied rectilinear motion in earlier standards.

- In rectilinear motion the force acting on the object and the velocity of the object both are along one and the same line.

- The distances are measured along the line only and we can indicate distances along the +ve and –ve axes as being positive and negative, respectively.

- The study of the motion of an object in a plane or in space becomes much easier and the corresponding equations become more elegant if we use vector quantities.

- In this Chapter we will first recall basic facts about rectilinear motion.

- We will use vector notation for this study as it will be useful later when we will study the motion in two dimensions.

- We will then study the motion in two dimensions which will be restricted to projectile motion only.

- Circular motion, i.e., the motion of an object around a circular path will be introduced here and will be studied in detail in the next standard.