If you're new in an engineering field, or if you're paying attention in school, you will have heard of models. I used to be confused when people described the equation of a falling body as a "physical model". Since, after all it's just a description of reality, right? What does it have to do with a model that for example architects build?

To summarize in one sentence: A model is a description of something, that allows you to predict what will happen under certain circumstances. If I hold an apple, and let go of it, how can you know that it will fall?

You can't, since the fall is going to happen in the future. And we don't know how to look into the future, it is impossible to know if the apple will fall.

The only reason you're very confident that it will fall is because you have seen it many times, and felt it, too. Your mind has built a model of gravity. A description that you can use to estimate/predict what will happen. It allows you to play with, or get a sense of, whatever system you're modeling, just like architects experimenting with their models.

However, this physical model is not reality. It is a simplification, since it wouldn't work in space, where things don't fall.