The core principle defines mechanical action $S$ as the temporal integral of the Lagrangian function, which is formulated as the difference between kinetic and potential energy in conservative systems within classical mechanics. This concept establishes that physical trajectories are determined by stationary values of this functional, governed strictly by Euler-Lagrange differential equations derived from variational calculus formalisms. It operates specifically within theoretical physics to provide a coordinate-independent framework for analyzing dynamics prior to deriving specific laws like Newton's second law through variation principles.
Prerequisite chain context: requires Integration over Space-Time Regions in Calculus.