Lagrangian mechanics is a reformulation of classical mechanics that focuses on the energy of a system rather than the forces acting on it. It uses the Lagrangian, which is defined as the difference between kinetic and potential energy. This approach simplifies the analysis of complex systems, especially when dealing with constraints or non-conservative forces. In Lagrangian mechanics, the equations of motion are derived from the principle of least action, which states that the path taken by a system is the one that minimizes the action. This method is particularly useful in fields like physics and engineering, where it can be applied to various mechanical systems.