THE LAW OF FALLING BODIES (Program 2)

Abstract

(Natural) philosophy is written in this enormous book, which is continuously open before our eyes (I mean the universe) but it cannot be understood without first learning to understand the language, and to recognize the characters in which it is written. It is written in a mathematical language. … Galileo Galilei, II Saggiatore (1623) HISTORICAL BACKGROUND Before we learned to read Galileo's mathematical book of the universe, our descriptions of nature were qualitative and verbal. For centuries, only words were used to describe the motion of objects, and those words were largely based upon the writings of Aristotle from the fourth century B.C. Aristotle's description of motion centered on the idea of a “natural place.” In his view earth had the lowest natural place, so naturally if you dropped a heavy object made of earth, it fell. Heavy bodies, containing more earth, fell faster than light ones. And any object, when released, initially gained speed toward its natural place. Aristotle's ideas present a qualitative (and apparently correct) description of motion. He believed that mathematics and precise quantitative measurement were of little value in describing the world around him. Nevertheless, Aristotle's doctrine did leave open the question, how does a falling body initially speed up? What rule does it follow? And so over a period of several centuries in the Middle Ages, various sages offered suggestions on this tricky question.