Centripetal acceleration is not a constant vector because its magnitude is constant, but its direction is continuously changing. This can be explained by considering an object moving in a circular path at a constant speed. The centripetal acceleration is always directed towards the center of the circle, and its magnitude is given by the equation:

a = v²/r

where v is the speed of the object and r is the radius of the circular path. It is important to note that the centripetal acceleration is always perpendicular to the velocity vector of the object.

Explanation:

1. Centripetal acceleration is the acceleration experienced by an object moving in a circular path. It is always directed towards the center of the circle and its magnitude is given by the equation a = v²/r, where v is the speed of the object and r is the radius of the circular path.

2. The centripetal acceleration is a vector quantity because it has both magnitude and direction. However, its direction is continuously changing as the object moves along the circular path.

3. The magnitude of the centripetal acceleration is constant throughout the motion of the object. This means that the object is experiencing a constant change in direction, but its speed remains constant.

4. Since the centripetal acceleration is always directed towards the center of the circle, its direction changes continuously as the object moves along the circular path. This is because the direction of the velocity vector of the object is also changing continuously.

5. Therefore, the centripetal acceleration is not a constant vector because its direction is continuously changing, even though its magnitude remains constant.

In conclusion, the centripetal acceleration is not a constant vector because its direction is continuously changing as the object moves along the circular path. Its magnitude, however, remains constant throughout the motion.