Today, we ask how fast things fall, and we rewrite
science. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
When Galileo was young, one
of his contemporaries used these words to describe
Aristotle's idea of how objects fall:
There is a natural place for everything to seek,
Heavy things go downward, Fire upward,
And rivers to the sea.
It was in the nature of falling, said Aristotle,
that heavy objects seek their natural place faster
than light ones -- that heavy objects fall faster.
Galileo took an interest in rates of fall when he
was about 26 years old and a math teacher at the
University of Pisa. It seemed to him that -- with
no air resistance -- a body should fall at a speed
proportional to its density. He decided to test
this modified Aristotelian view by making an
There was no tradition of describing experimental
research in Galileo's day. Controlled experiments
were almost unknown. So Galileo's report was pretty
skimpy. He seems to have dropped different balls
from a tower. But what weights? What tower? We can
be pretty sure it was the Leaning Tower of Pisa.
But we end up doubting whether or not he really did
the experiment. Maybe he just reported what he
thought should have happened.
One result of the experiment surprised Galileo, and
one surprises us. Galileo found that the heavy ball
hit the ground first, but only by a little bit.
Except for a small difference caused by air
resistance, both balls reached nearly the same
speed. And that surprised him. It forced him to
abandon Aristotelian ideas about motion. If he
really did the experiment, it was surely a turning
point in the history of science.
But what surprises us is what Galileo says happened
just after he released the two balls. He says the
lighter ball always started out a little bit faster
than the heavy ball. Then the heavy ball caught up.
That sounds crazy.
So Thomas Settle and Donald Miklich reran
Galileo's tower experiment in front of a camera. An
assistant held four-inch iron and wooden balls at
arm's length -- as Galileo would have to have held
them to clear the wide balustrate atop the Pisa
tower. It turns out that when you try to drop them
both at once, your strained muscles fool you. You
consistently let go of the lighter one, the one
you've been gripping less intensely, first. That
means Galileo accurately reported what he
seen happening. And we're left with no doubt
that he actually did do the experiment.
Galileo went on to become the first real challenger
of Aristotle. His tower experiment was no fable --
no apple falling on Newton's head. This was one of
the first controlled scientific experiments. Like
most of today's experiments, it was imperfect. But
this experiment changed Galileo, and it changed
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds