How to Find Lagrangians

Lagrange’s equations are a system of second-order differential equations. In order to use them to compute the evolution of a mechanical system, we must find a suitable Lagrangian for the system. There is no general way to construct a Lagrangian for every system, but there is an important class of systems for which we can identify Lagrangians in a straightforward way in terms of kinetic and potential energy. The key idea is to construct a Lagrangian L such that Lagrange’s equations are Newton’s equations \displaystyle{\vec F = m \vec a}.

— 1.6 How to Find Lagrangians

— Structure and Interpretation of Classical Mechanics



2020.12.06 Sunday ACHK