If an object moves in a straight line with position function s = f(t), then the average velocity between t = a and t = b is f(b) − f(a)/b − a
and the velocity at t = c is f '(c). Thus the Mean Value Theorem tells us that at some time t = c between a and b the instantaneous velocity f '(c) is equal to the average velocity. For instance, if a car traveled 150 km in 2 hours, then the speedometer must have read km/h at least once.
In general, the Mean Value Theorem can be interpreted as saying that there is a number at which the instantaneous rate of change is equal to the average rate of change over an interval.