What is the driving force of ocean currents and atmospheric movement? A. The gravity of the Sun
B. Rotations of Earth
C. The Moon's gravity
D. Unequal heating of Earth by the Sun

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.