A model of intelligibility in science: Using Galileo's balance as a model for understanding the motion of bodies

Abstract

In 1590, or thereabouts, Galileo wrote the manuscript De Motu (Galileo 1590). In this text he attempted to demonstrate the errors of Aristotelian natural philosophy and began his lifelong attempt to construct a science of motion. The chief device in De Motu was his wide ranging use of the balance. The balance was a simple machine, familiar to all, that Galileo could describe using principles of equilibrium. In this paper we suggest an empirical thesis: Galileo understood something important when he used the balance as the basic equilibrium model in order to understand all the phenomena of motion. Galileo used the balance model to make intelligible problems of dynamics as well as kinematics (as we anachronistically call them). We believe that using the Galilean balance equilibrium model today in physics classes at the secondary and college levels (and probably even at the elementary school level) would provide students with a model of intelligibility that would unify their thinking about motion and, at the same time, provide them with a general procedural schema for solving motion problems.