By Because we calculate the speed in terms of distance, we do not consider the direction when we calculate the speed. Therefore, it must be clear to you by now, that the speed is a scalar quantity. The velocity however, is defined as the rate of change of the displacement. Therefore, it is a vector quantity that has both a magnitude and a direction.
The velocity of an object can be obtained by dividing its displacement by time.
We learnt earlier that sometimes, bodies could move with uniform speeds while at other times they could move with non-uniform speeds. In a similar manner, the velocity of a body too can be uniform during certain time intervals while it can be non-uniform at other intervals.
The table below shows the displacement of a body along a specific direction, at the end of each 1 s time interval, as measured from the starting point.
Since the increase in the displacement of the body during each second is 3 m, the motion has taken place at a constant or uniform velocity.
When a body is moving at a constant velocity, neither the magnitude nor the direction of its velocity changes with time.
If a body moves along a straight line at a constant velocity of 6 m s-1, then the change in the displacement during each 1 s interval is 6 m. The direction of the
motion too remains constant. If the body moves at this constant velocity for 5 s, then its displacement after 5 s = 6 m s-1× 5 s = 30 m.
That is, for a body moving at a constant velocity, the displacement after a certain time interval can be obtained by multiplying the velocity by the relevant time
interval.
The following table shows the displacement of another object moving on a straight line, as measured during each 1 s time interval.
The displacement of this object is 4 m in the first second, 3 m in the second second, and 2m in the third second etc. As the displacement is not the same in every second, the velocity of the object is not uniform. In such occasions we can calculate the mean velocity.
