Final answer:
When acceleration is perpendicular to velocity, the object exhibits uniform circular motion with constant speed, and the acceleration, called centripetal, changes only the velocity's direction.
Step-by-step explanation:
When the acceleration of an object is always directed perpendicular to its velocity, the object is undergoing uniform circular motion. In this case, the speed of the object remains constant because the perpendicular acceleration is changing only the direction of the velocity, not its magnitude. This perpendicular acceleration is known as centripetal acceleration, which always points toward the center of the circle along which the object is moving. It's important to note that centripetal acceleration is necessary for an object to maintain this circular trajectory.
Situations involving constant acceleration typically involve a linear change in velocity. However, when we observe motion along circular paths, such as a car turning a corner at constant speed, the acceleration we experience is not due to a change in speed but a change in direction. This can be understood by examining uniform circular motion, where, despite the speed being constant, the acceleration continually acts perpendicular to the instantaneous velocity, thereby altering only the direction of velocity at a constant rate.