Final answer:
The average velocity that Lillian rides her bicycle at is defined as the displacement (change in position) over the travel time, which makes option C) the correct answer.
Step-by-step explanation:
Lillian rides her bicycle along a straight road at an average velocity, which is defined as the displacement (change in position) divided by the travel time. Therefore, the correct answer is C) Change in position over time. Unlike speed, which only considers the total distance traveled without the direction, velocity is a vector quantity and takes into account the direction of travel. In equation form, average velocity can be represented by the ratio of displacement to time (v = Δx/Δt, where Δx represents displacement, and Δt represents time).
When calculating average speed, you use the total distance traveled divided by the travel time. This is different from average velocity because it does not take into account the direction of the movement. For example, if you were to calculate average speed using the odometer reading divided by travel time during a car trip, you would not be considering the direction, which could lead to different values for average speed and magnitude of average velocity under certain circumstances.