Part I: The Early Years

Galileo Galilei was born near Pisa in 1564 -- the same year in which Shakespeare was born and the year in which Michelangelo and Calvin died.

After studying at the University of Pisa, he was appointed to the chair of mathematics -- but as this picture of Pisa reminds us,

it was a Pisa, of course, that the famous leaning tower might well have suggested Galileo's most famous experiment.

The computer animation linked to this picture, illustrates what Galileo's demonstration would have shown.

First of all the theory which virtually everyone accepted at the time was the traditional theory of Aristotle, who believed that heavier objects fall more quickly than lighter ones.

Consider, for example, two objects -- one twice as heavy as the other. Imagine Aristotle at the top of the leaning tower of Pisa, dropping off two cannonballs, one twice as heavy as the other. According to Aristotle, it should fall twice as fast. If it were four times heavier, it should fall four times faster.

But in fact, what the leaning tower of Pisa type of experiment demonstrates, when actually performed,

is that Aristotle was wrong, that no matter what the difference in weight, two heavy objects will fall simultaneously at virtually the same speed.

Recently it has been fashionable to question whether or not Galileo ever dropped anything off the campanile -- or leaning tower -- of the Duomo in Pisa. If he did so, it certainly could not have been an "experiment" in the modern sense of the word -- can you imagine running up and down the leaning tower of Pisa -- trying to drop objects of different weights simultaneously, from the edge of the tower, at the very same time, which is not easy to do, and then observe how quickly they fall, especially when the time elapsed would only have been a matter of seconds -- and nothing like the stop watch or any other convenient device -- had been invented yet?

Actually, whether or not Galileo ever performed his famous experiment on the leaning tower hardly seems to matter -- a similar experiment-demonstration had already been published by Benedetti Giambattista in 1553, and the test had also been made and published by the Flemish engineer Simon Stevin in 1586.

As for Galileo's interest in disproving Aristotle's Theory about falling objects, years later he said that he had first thought about this during a hailstorm, when he notice that both large and small hailstones hit the ground at the same time.

If Aristotle were right, this could only happen if the larger stones dropped from a higher point in the clouds -- but at virtually the same time -- or that the lighter ones started falling earlier than the heavier ones -- neither of which seemed very probable to Galileo. Instead, the simplest explanation was simply that heavy or light, all hailstones fell simultaneously with the same speed.

Go to the next section: Galileo II: Heavenly Bodies

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