Physics is a tough subject in part because it is very big. …

You can think of physics as being divided along three lines.
Galilean vs Einsteinian
Non-statistical vs statistical mechanics
Classical vs Quantum
The first of these divisions refers to what is usually called "nonrelativistic" vs the "relativistic" physics of Einstein. However, the Principle of Relativity, which says that any body in uniform motion can consider itself "at rest" from its own perspective and will observe identical physics, was first stated by Galileo. Thus all physics since the Renaissense has been relatavistic.

However, there are really only 6 regions because some possibilities don't really work. In particular, if you are doing Einsteinian physics, then you can't really have quantum mechanics or statistical mechanics without the other. Classical einsteinian statistical mechanics leads directly to quantum mechanics via the ultraviolet catastrophe. Einsteinian quantum mechanics naturally

I keep messing up and posting these things when I don't intend to.