The Poet and the Pendulum

Abstract.

We begin with the pendulum and the curious authority of the expression for the period of its swing, $T = 2\pi \sqrt {l/g}$. That this is not an empirical result −π is an irrational number -leads to an examination of the nature of physics. In the course of things, we come to Plato’s critique of poetry in The Republic and the fundamental differences he points to between the authority of the particular and that of reason. Extending this distinction to physics, we show how the study of the pendulum illustrates Plato’s project. The study of the pendulum not only prompts the question, “What is the nature of physics?” it also proves to be an excellent way for students to come to appreciate the kind of reasoning that is at the heart of physics.