As it turns out, this experiment was known centuries
before Galileo. For example, Philoponus wrote (in the
6th century!):
"If you let fall from the same height two weights,
of which one is many times as heavy as the other,
you will see that the ratio of the times required
for the motion does not depend on the ratio of the
weights, but that the difference in time is a very
small one" -- Philoponus
The question naturally arises: How did Aristotelian
physics manage to survive for several hundred more
years in the face of this empirical refutation?
Were the results suppressed by Church Dogma or thru
the political influence of the Aristotelian Fundies?
No, the reason was twofold: (1) The preponderance of
empirical evidence supported Aristotelian physics and
(2) to displace an established theory its detractors
must do more than throw out a few embarrassing facts.
They have to have a new theory that explains as much
as the old theory did and then some.
The nature of the empirical evidence for Aristotelian
physics is very interesting. Let's take the example
in the quote above. It turns out that the cited case
is just one exception to an otherwise remarkable
success of Aristotelian physics. If one drops objects
of different weights in a fluid one finds that the
time required to traverse some distance is proportional
to the weight, just as predicted. Thus, Galileo could
not just point to the exception. He had to develop
a theory which explained why Aristotelian physics
worked with fluids and not with air.
There is another more humorous example of empirical
support for Aristotelian physics. In his book
<The Birth of a New Physics>, Bernard Cohen gives
a reproduction of a funny drawing which looks like
a political cartoon taken from a modern newspaper.
The drawing suggests an experiment for testing
Galileo's ideas about falling bodies and seems
obviously intended to poke fun at Galileo. The
drawing contains a cannon pointing straight into
the air with smoke coming out of the barrel to
indicate that it has just been fired. Two fellows
are standing next to the cannon staring up into
space. One is wearing Priestly robes while the
the other wears a large brimmed hat and a cape.
Perhaps this is supposed to be Galileo. Anyway,
the caption for the little "cartoon" reads:
"Will it fall back down again?"
Exactly how this is a test of Aristotelian physics
and a ridicule of Galileo is not immediately
obvious to those of us who take Newton for granted.
Here's the idea in a nutshell. Once the cannon ball
leaves the barrel of the cannon it is no longer in
physical contact with the earth and so its motion
cannot be influenced directly by the motion of the
earth (supposing the earth were moving). Thus, if
the earth were really moving it would leave the
cannon ball behind (so to speak). It would not
fall straight back to the ground but would instead
land many hundreds of miles away or perhaps, if the
cannon is powerful enough, become lost in space.
And so we see the humor of the cartoon. "Will it fall
back down again?" Yes, of course, and it might even
hit that silly scientist on the head. It is thus
obvious even to a child that the earth cannot possibly
be moving :). <<refuting this turns out to be not
quite so simple as it seems, there is a combination
of everyday common sense with the established physics
of the time>>
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"If cucumbers had anti-gravity,
sunsets would be more interesting"
-- Wesley Elsberry