1. (used with a sing. verb) The science of matter and energy and of interactions between the two, grouped in traditional fields such as acoustics, optics, mechanics, thermodynamics, and electromagnetism, as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics, and plasma physics.

2. (used with a pl. verb) Physical properties, interactions, processes, or laws: the physics of supersonic flight.

3. (used with a sing. verb) Archaic The study of the natural or material world and phenomena; natural philosophy.