Explain average velocity and average speed.

(N/A) When an object is in motion,its position changes with time. The rate at which it changes its position can be found in two ways.
If we only consider the time rate of change of distance,it is speed. If we consider the time rate of change of position with direction,it is velocity.
Speed: The distance covered by an object in unit time is called speed.
Average speed: The ratio of the total distance covered during a journey to the total time taken is called average speed.
Its $SI$ unit is $m s^{-1}$ and it is a scalar quantity. Hence,its value is always positive.
Velocity: The displacement covered in unit time is called velocity. It is a vector quantity.
Average velocity is defined as the change in position or displacement $(\Delta x)$ divided by the time interval $(\Delta t)$ in which the displacement occurs:
$\bar{v} = \frac{x_{2} - x_{1}}{t_{2} - t_{1}} = \frac{\Delta x}{\Delta t}$
where $x_{2}$ and $x_{1}$ are the positions of the object at times $t_{2}$ and $t_{1}$ respectively. The $SI$ unit for velocity is $m s^{-1}$,although $km h^{-1}$ is used in many everyday applications.
For motion in a straight line,the directional aspect of the vector can be represented by '$+$' and '$-$' signs,and we do not have to use vector notation for velocity.
The magnitude of average velocity can be positive,negative,or zero.
Average speed is always greater than or equal to the magnitude of average velocity. For uniform motion,velocity is equal to average velocity at every moment.
The figure shows the $x-t$ graph for the motion of a car,where the portion between $t = 5 \ s$ and $t = 7 \ s$ is highlighted to calculate average velocity.