The arrows below represent the velocities of two vehicles. Bus
Which claim explains why the velocity of each vehicle is a vector quantity?
It can change over time.
It has direction and size.
It is a measurable quantity.
It uses a measure of speed.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.