Lithium is a metal that is frequently used in rechargeable batteries for mobile devices. The sample of lithium has a mass of 13.1 grams and a volume of 24.5 millimeters . If you dropped this pece of Lithium in water(witha density of 1.0 g/ml) it would

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.