Acceleration describes how velocity is changing over time, and velocity describes how position is changing over time. When acceleration is positive, velocity is increasing; when acceleration is negative, velocity is decreasing. When acceleration is zero, velocity remains unchanged.
For example, if a car is traveling at a constant speed of 60 mph, its acceleration is zero, but its velocity is not at a maximum. The car's velocity could be increased to 70 mph, 80 mph, or any other speed, all while maintaining an acceleration of zero.
Similarly, if a car is stopped at a red light, its acceleration is zero, but its velocity is not at a maximum. The car's velocity could be increased to 1 mph, 10 mph, or any other speed by applying positive acceleration.
Therefore, acceleration and velocity are two independent quantities that can vary independently of each other.
