Mainly when the velocity is constant.
When there is no acceleration or when there is constant acceleration. When either of these cases is present, the graph of velocity versus time will be linear. When there is linear velocity, the average velocity will equal the instantaneous velocity at any point on the graph.
When an object is in constant motion (when there is no acceleration). At any point in that motion the average and instantaneous velocities will be the same.
The average acceleration of an object is equal to the instantaneous acceleration of that object if the acceleration is constant (i.e. linear when graphed). However, when there is not constant acceleration, there is no guarantee that the average acceleration is equal to the instantaneous acceleration (i.e. non-linear when graphed).
If the object begins from rest and a constant force is applied to it, then at the end of one second, the magnitude of its velocity is numerically equal to the magnitude of its average acceleration, although the units are different.
For the instantaneous value of average velocity, average speed and average velocity are equal.
At a small time interval, the average velocity is approximately equal to the instantaneous velocity. However, the values of the average velocity and the instantaneous velocity approach each other , as the length of the time interval is decreased more and more.
In uniform motion.
If the velocity is constant (i.e., there is no acceleration). Terminal velocity is an example, although any constant velocity would fit this description.
Average acceleration will be equal to instantaneous acceleration when an object has an uniform acceleration throughout its motion. Example : A car accelerating at 1m/s2 uniformly in a straight line.
Mainly, when the velocity doesn't change. Also, in the case of varying velocity, the instantaneous velocity might, for a brief instant, be equal to the average velocity.
It equals an undefined entity. The average acceleration of an object equals the CHANGE in velocity divided by the time interval. The term "change in velocity" is not the same as the term "velocity", "average velocity", or "instantaneous velocity".