Action

In physics, action is a scalar quantity that describes how the balance of kinetic versus potential energy of a physical system changes with trajectory. Action is significant because it is an input to the principle of stationary action, an approach to classical mechanics that is simpler for multiple objects.[1] Action and the variational principle are used in Feynman's formulation of quantum mechanics[2] and in general relativity.[3] For systems with small values of action similar to the Planck constant, quantum effects are significant.[4]