To discuss the motion in detail, one very important parameter of motion i.e. velocity should be explore in easier manner. To understand the concept of velocity consider the following example,
Imagine a boy running on ground, started his motion from point P, reaches to points Q, then R and finally stopped at point S, as shown in figure. The distances traced in each intervals is say x1, x2 and x3 and the time required for the same is t1, t2 and t3 respectively. Here P is initial position and S is final position. Then the shortest distance between the points P and S is PS.
Hence here d(PS) will be the displacement of the boy during its motion.
Let d(PS)= ∆x
And the time require to complete this motion is say,
Then the ‘velocity of body is defined as the rate of change of displacement’ or ‘displacement of body per unit time is known as velocity.’
Then,
Velocity = displacement/time
V = ∆x/∆t
Since the displacement is vector quantity, velocity is also vector.
SI unit of velocity is meter/second (m/s)