INTRODUCTION

A body is said to be at rest, if it occupies the same position with respect to its surroundings at all moments. But it is said to be in motion, if it changes its position, with respect to its surroundings.

IMPORTANT TERMS

The following terms, which will be frequently used in this chapter, should be clearly understood at this stage :

1. Speed. The speed of a body may be defined as its rate of change of displacement with respect to its surroundings. The speed of a body is irrespective of its direction and is, thus, a

scalar quantity.

2. Velocity. The velocity of a body may be defined as its rate of change of displacement, with respect to its surroundings, in a particular direction. As the velocity is always

expressed in particular direction, therefore it is a vector quantity.

3. Acceleration. The acceleration of a body may be defined as the rate of change of its velocity. It is said to be positive, when the velocity of a body increases with time, and

negative when the velocity decreases with time. The negative acceleration is also called

retardation. In general, the term acceleration is used to denote the rate at which the velocity

is changing. It may be uniform or variable.

4. Uniform acceleration. If a body moves in such a way that its velocity changes in equal magnitudes in equal intervals of time, it is said to be moving with a uniform acceleration.

5. Variable acceleration. If a body moves in such a way, that its velocity changes in unequal magnitudes in equal intervals of time, it is said to be moving with a variable acceleration.

6. Distance traversed. It is the total distance moved by a body. Mathematically, if body is moving with a uniform velocity (v), then in (t) seconds, the distance traversed s = vt

In this chapter, we shall discuss the motion under uniform acceleration only.

MOTION UNDER UNIFORM ACCELERATION

MOTION UNDER FORCE OF GRAVITY