The focus of physics studies is on forces. Those are the result of combinations of matter and energy.
Of the many physics equations, the three sets that may define it most succinctly as a field are Newton’s Equations of Motion, Maxwell’s Equations of Electromagnetism, and Einstein’s Equations of Relativity, including that most famous (simplified) form of
Everything else, from particle physics to astronomy examines how matter and energy interact in our universe based for the most part on those equations.
That is what distinguishes it from chemistry (which also overlaps many areas of atomic and sub-atomic particles), which is more focused on combinations of matter; biology, which is focused on particular systems that are living organisms; and the Earth Sciences, which are primarily concerned with geological systems.
All of the sciences overlap in their areas of investigation, and they all are linked by the common use of mathematics. But Physics retains its peculiar characteristics defined as noted above.