Answer :
The correct person is Carrie because acceleration includes velocity and velocity is the change of direction. I just answered this on a test today
Answer: Carrie
Acceleration is change of velocity with time. It is a vector quantity which means it has both magnitude and direction.
A change in velocity can occur when there is change speed or direction thus causing acceleration. As the carousel horses are going around and around and bobbed up and down, it means there was definite change in direction. This means there was certain change in velocity. we cannot say about the magnitude of the velocity (speed) but definitely Carrie and Sam were accelerating. Hence, Carrie's response is fully correct.