Is it wierd if i think my step sis is thick

yes it is and sometimes it's not

Explanation:

technically she isn't

related to you, however she is family, so it makes it sort of weird.

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.