Question

differentiate between average acceleration and instantaneous acceleration.

Answer 1

Average acceleration is the average velocity per unit time
whereas instantaneous acceleration is the acceleration at the certain instant of time.
The value of average acceleration is generally determined by
       a(average)=Δv/Δt
 Here Δ refers to a big change in velocity

the value of instantaneous acceleration  is generally determined by
        a(inst)=dv/dt
here "d" refers to a very small instant.

Answer 2

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Average acceleration is the change of velocity over a period of time. Instantaneous acceleration is the change of velocity over an instance of time. Constant or uniform acceleration is when the velocity changes the same amount in every equal time period.