Final answer:
All three motions: speeding up, slowing down, and turning are considered acceleration. Acceleration encompasses any change in velocity, whether it's a change in magnitude (speeding up or slowing down) or direction (turning).
Step-by-step explanation:
The question asks which of the following types of motion are considered acceleration: an object speeds up, an object slows down, and an object turns. In physics, acceleration is defined as the rate of change of velocity. This includes both an increase and a decrease in speed, as well as a change in direction. Therefore, the correct answer is d. a, b, and c, meaning that all three motions listed—speeding up, slowing down, and turning—are forms of acceleration.
Speeding up results in positive acceleration, while slowing down results in negative acceleration. However, both are considered acceleration because they represent a change in the magnitude of velocity. Lastly, an object turning experiences centripetal acceleration, which is always directed towards the center of the circular path, representing a change in the direction of the velocity vector.
Furthermore, acceleration is not just a change in speed but also includes directional changes. Thus an object moving in circular motion is also accelerating, as it's constantly changing its direction of motion, even if its speed remains constant.