Final answer:
Acceleration in roller coaster physics is the rate of change in velocity, encompassing both changes in speed and direction.
Step-by-step explanation:
The scientific definition of acceleration in the context of roller coaster physics is the rate of change of velocity, which can involve changes in the speed or direction of the object or both. Acceleration is not simply an increase in speed; any change in speed (faster or slower), as well as changes in the direction of movement, all constitute acceleration. This is particularly relevant for roller coasters as they involve significant changes in both speed and direction, such as when a roller coaster car speeds up going down a hill, slows down going up the next, or changes direction in a loop or turn, thereby continuously experiencing acceleration.