Rolling Balls and Falling Ideas: Galileo’s Ramp Data

Testing Old Ideas

1The Renaissance began in Italian city-states in the 1300s and 1400s, as scholars and artists studied ancient Greek and Roman works and also looked hard at the world around them. Artists such as Leonardo da Vinci and Michelangelo studied muscles and bones so that the bodies they painted and carved would look real. Michelangelo’s marble David, finished in 1504, even shows the veins in the hands. Leonardo (1452–1519) dissected human bodies and filled notebooks with careful drawings of the heart and skeleton. The notebooks were never printed in his lifetime, and most of his anatomy drawings stayed unknown for centuries.

2Andreas Vesalius, a doctor who taught at the University of Padua, also dissected human bodies himself instead of only reading Galen, an ancient Greek doctor whose books had been taught for more than a thousand years. Galen had studied mostly animals, and Vesalius found mistakes, such as Galen’s claim that the human lower jaw is made of two bones. In 1543 Vesalius published The Fabric of the Human Body, with more than 200 detailed woodcut pictures. Because the pictures were printed, readers in many cities saw exactly the same images.

3Galileo Galilei (1564–1642) tested ancient ideas about motion. The Greek thinker Aristotle had taught that heavier objects fall faster than lighter ones. A famous story says Galileo dropped balls from the Leaning Tower of Pisa, but many historians doubt it happened. His own writings describe a different test. A falling ball moved too fast to time, so he let a bronze ball roll down a long, smooth groove in a tilted board. To measure time, he let water run from a large container through a thin pipe into a cup and then weighed the water.

4The ball did not roll at a steady speed. Galileo also argued that if air did not slow them down, heavy and light objects would fall at the same rate.

5Galileo pointed telescopes at the sky as well. In late 1610 he saw that Venus changes shape like the Moon, from a nearly full disk to a thin crescent. In the older view, Venus circled Earth while staying between Earth and the Sun, so it could never look nearly full. A Venus that circles the Sun could show every phase.

6In 1633 a Church court found Galileo guilty of teaching that Earth moves around the Sun, and his books were banned from being printed. His last book, Two New Sciences, which describes his ramp tests, was printed in 1638 in Leiden, in the Dutch Republic, where the ban had little force.