Question

Acceleration is the rate at which velocity changes, which means you accelerate anytime you speed up, slow down, or change

Answer 1

Since velocity is a vector quantity, it has both direction and magnitude(speed) associated with it. Whenever we change the speed(up or down), the velocity changes, though the direction of velocity need not change. In a different scenario, we may be changing the direction of the velocity keeping the speed constant(e.g, uniform circular motion). Or we may have a case when both the speed and direction change simultaneously, In all the cases the acceleration is produced(since acceleration is itself a vector quantity).