Speed, Velocity and Acceleration

In motion, it is important to understand some quantities involved with the movement of a body in a straight line. The essential quantities are distance, displacement, speed, velocity and acceleration.

 Speed

The speed of a body in motion is the rate at

which it covers a distance.

Speed = distance/time

The S.I unit of speed is meter per second (ms^-1) because the S.I unit of distance is meter and that of time is seconds. Other units of speed is kilometers per hour and centimeters per second.

For example:

If a car travels a distance of 400km in 5hours, its average speed is then; 400km/5hours = 80km/hr.

Uniform Speed

Uniform or constant speed occurs when a body covers equal distances in equal time intervals irrespective of the amount of time.

Velocity

Speed and velocity are two quantities sometimes used interchangeably. In speed, distance is quantified with no direction while velocity is expressed in terms of displacement with specified direction.

Velocity can be defined as the rate of change of displacement.

Velocity = displacement/time

Velocity has the S.I unit as speed (meter per second).

Uniform velocity

Uniform or constant velocity occurs when a body travels with equal displacements in equal time intervals irrespective of the amount of time.

But, a body moving in a circular motion travels with non-uniform velocity because its direction of motion is not fixed, it changes continuously.

Instantaneous velocity

Instantaneous velocity can be defined as the velocity of a body at any particular instant of time.

Acceleration

When a body moves in a specified direction, it changes its velocity with respect to time. This change in velocity with time is referred to as acceleration.

Acceleration = Change in velocity/ time taken for the change

Its S.I unit is meter-per-second-per-second (ms^-2).

Note:

Acceleration occurs when a body increases its velocity with time while retardation occurs when the body decreases its velocity with time (negative acceleration).

Acceleration = final velocity – initial velocity

                                                Time

                a = v - u                                hence, v = u + at

                         t

Uniform acceleration

Uniform or constant acceleration occurs when a body moves with equal velocity in equal amounts of time irrespective of the amount of time.