Final answer:
Velocity is the vector version of speed that includes both speed and direction, representing the rate of change in an object's position over time. Acceleration is the rate of change of velocity. The correct answer is (c) Rate of change of velocity, which accurately describes acceleration.
Step-by-step explanation:
Velocity is the vector version of speed and is concerned with how fast an object moves, which includes both the speed and the direction of motion. Specifically, velocity represents the rate of change in an object's position over time. Therefore, the physical quantity that changes over time when discussing velocity is the object's position. It's important to note that the velocity of an object can be described as either average velocity, which is displacement divided by the time over which the displacement occurs, or instantaneous velocity at a specific moment.
Acceleration, on the other hand, is the rate of change of velocity, which means it indicates how quickly the velocity of an object is changing in terms of both speed (magnitude) and direction. If an object is changing its speed or direction, it is undergoing acceleration. For example, even if a car turns a corner at a constant speed, it is accelerating because its direction is changing. When velocity changes, either in magnitude or direction, acceleration occurs.
So, regarding the question on the physical quantity that velocity defines as changing over time, we are referring to the object's position. This aligns with the options provided:
- Change in velocity
- Change in momentum
- Rate of change of velocity
- Rate of change of momentum
The correct answer is (c) Rate of change of velocity, since it most accurately describes what velocity indicates with respect to time. However, keep in mind that this is a description of acceleration, not velocity itself. Velocity describes the change in position over time, whereas acceleration is the rate at which velocity itself changes.