Plz help A student determines that the mass of a metal rod
is 12.0 g. He places 10.0 mL of water in a 25 ml
graduated cylinder. When the metal rod is placed
in the water, the graduated cylinder then reads
15,0 mL. What is the density of the metal rod?

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.