The Law of Falling
Objects
Year of Discovery: 1598
What Is It? Objects fall at the same speed regardless of their weight.
Who Discovered It? Galileo Galilei
Why Is This One of the 100 Greatest?
It seems a simple and obvious discovery. Heavier objects don’t fall faster. Why does it
qualify as one of the great discoveries? Because it ended the practice of science based on the
ancient Greek theories of Aristotle and Ptolemy and launched modern science. Galileo’s
discovery brought physics into the Renaissance and the modern age. It laid the foundation
for Newton’s discoveries of universal gravitation and his laws of motion. Galileo’s work
was an essential building block of modern physics and engineering.
How Was It Discovered?
Galileo Galilei, a 24-year-old mathematics professor at the University of Pisa, Italy,
often sat in a local cathedral when some nagging problem weighed on his mind. Lamps
gently swung on long chains to illuminate the cathedral. One day in the summer of 1598,
Galileo realized that those lamps always swung at the same speed.
He decided to time them. He used the pulse in his neck to measure the period of each
swing of one of the lamps. Then he timed a larger lamp and found that it swung at the same
rate. He borrowed one of the long tapers alter boys used to light the lamps and swung both
large and small lamps more vigorously. Over many days he timed the lamps and found that
they always took exactly the same amount of time to travel through one complete arc. It
didn’t matter how big (heavy) the lamp was or how big the arc was.
Heavy lamps fell through their arc at the same rate as lighter lamps. Galileo was fascinated. This observation contradicted a 2,000-year-old cornerstone of beliefs about the
world.
He stood before his class at the University of Pisa, Italy, holding bricks as if weighing
and comparing them—a single brick in one hand and two bricks that he had cemented together in the other. “Gentlemen, I have been watching pendulums swing back and forth.
And I have come to a conclusion. Aristotle is wrong.”
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