Adiabatic invariant

An adiabatic invariant is a quantity that remains constant when changes are made to a system very slowly, or adiabatically, compared to the timescales of the system's dynamics. The concept is often discussed in the context of classical mechanics, quantum mechanics, and thermodynamics. ### In Classical Mechanics In classical mechanics, one of the most well-known adiabatic invariants is the action variable, which is defined in the context of a periodic motion.