👉 In physics, a Lagrangian is a function that describes the dynamics of a system. It quantifies how much force is needed to change the state of the system from one configuration to another. The Lagrangian can be expressed in terms of the action and the potential energy functional, which are functions of the position and momentum of the system. The Lagrangian is used to find the equations of motion for a system, which are the equations of motion that describe how the state of the system