Answer:
Sometimes the phenomena are too complex to be actually explained in totality. In these cases, in order to explain the phenomena, the scientist needs to "simplify" the phenomena.
They can do it by idealizing some things, supposing that some things do not change, and things like that. This is called a "model" of the phenomena. This model helps to explain and work (to a certain extent) with this phenomena, because makes it a lot simpler to work with (experimental wise and mathematical wise)
