OED Definition (1b): The branch of science concerned with the nature and properties of non-living matter and energy, in so far as they are not dealt with by chemistry or biology; the science whose subject matter includes mechanics, heat, light and other radiation, sound, electricity, magnetism, gravity, the structure of atoms, the nature of subatomic particles, and the fundamental laws of the material universe. Also: the physical properties and phenomena of a thing. (1)
By far the longest OED definition for the sciences. Physics is, in a way, the science of everything as it studies the tiniest constituents of the universe and how they act together on the grandest scale. Here you get the latest technology, electronics, particle accelerators, we find out what light is made of and, in general, why everything is the way it is.
- Particle Physics (studying the smallest parts of the universe and how they interact to create the universe we know).
- Mechanics (probably one of the oldest branches of science, studying how larger thing’s interact with each other in a physical sense).
- Quantum Physics (damned if I know).