PHYS112 Lecture : Lagrangian Method.pdf
Document Summary
Copyright 2007 by david morin, morin@physics. harvard. edu (draft version) In this chapter, we"re going to learn about a whole new way of looking at things. Consider the system of a mass on the end of a spring. We can analyze this, of course, by using f = ma to write down m x = kx. The solutions to this equation are sinusoidal functions, as we well know. We can, however, gure things out by using another method which doesn"t explicitly use f = ma. In many (in fact, probably most) physical situations, this new method is far superior to using f = ma. You will soon discover this for yourself when you tackle the problems and exercises for this chapter. We will present our new method by rst stating its rules (without any justi cation) and showing that they somehow end up magically giving the correct answer. We will then give the method proper justi cation.
