Domains of Physics

Classical mechanics governs macroscopic, slow (v≪c), large (scale ≫ atomic) systems.

Thermodynamics deals with heat, work, and statistical behavior of large ensembles.

Electromagnetism unifies electric and magnetic phenomena (Maxwell's equations).

Optics is a special case of EM — wave + ray + quantum (photon) descriptions.

Special relativity kicks in for v comparable to c; General relativity for strong gravity.

Quantum mechanics governs atomic and subatomic scales.

Nuclear and particle physics probe the constituents of matter.