Volocity
Velocity is defined as measure of displacement covered with the passage of time.
Mathematically velocity is calculated by dividing the displacement covered by the time taken.
Unit of velocity is, therefore, m/s and dimensions are [LT-1].
Velocity is a vector quantity
We know that a vector can be multiplied by a scalar. Doing so, the product is a vector quantity. Its magnitude is the ‘scalar times the magnitude of the original vector and the direction depends on the sign of the scalar’. Now consider the equation of velocity,
Here, the displacement vector is multiplied by the scalar time, and the product velocity must be a vector quantity. Since time is always positive, therefore, its direction will be along the displacement.
Average Velocity
Average velocity is defined as “it is the total displacement S divided by total time t. Hence average velocity is the net displacement per unit time.
Thus average velocity gives us information over the total time t. It does not give us enough details about the velocity during the given instant of time.
Instantaneous Velocity
Average velocity does not convey complete details of the motion during the time duration in which it is calculated.
Instantaneous velocity is defined as, “in the limit when Δt tends to zero, the ratio 
approaches a definite value called instantaneous velocity.” Mathematically,
Let you drive a car. Many times you speed up or slow down according to the situation. When you reach your destination you can calculate your average velocity by dividing total displacement over time. However, it doesn’t tell more about your journey, i-e, when you speeded up, when you slowed down and when you changed direction. These details are described by your instantaneous velocity.
Uniform Velocity
If a body covers equal displacements in equal intervals of time then the body is said to be moving with uniform velocity.
In case of uniform velocity, the average and instantaneous velocities of the body are equal.
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