Re: Galileo's Freefall Experiment

["David J. Hamilton" <djhamil@teleport.com>]

At the risk of oversimplification:

The Greek mindset was that gravity was a driving force which was located 
inside the body- e.g., a rock's "gravitas" is what propels it downward.  
It is also part of the Greek (at least Aristotle's) mindset that there 
can be no vacuum, therefore, it would be unthinkable to "remove" the air 
resistance.  If all the world is composed of earth, air, fire, and water, 
then a moving body must move through something.  Gravity is simply the 
property of "heavy" matter (composed mostly of earth) that causes it to 
seeks its natural place near the center of the world (and below matter 
which is less heavy).  Objects with a greater proportion of earthly 
matter (such as a rock) will fall faster than objects which contian less 
earthly matter (such as a feather).  There's no need for imagining 
retarding forces when differing rates of fall can be explained in this 
way. 

My recollection is that Galileo's mind experiment was intended to show 
that objects of equal density will reach the ground at the same time.  At 
the time he wrote the passage in question, he believed that falling 
bodies would accelerate until they reached a terminal velocity which was 
dependent on the density of the body.  I don't recall of he considered 
air to be a force acting on the falling body or a resistance through 
which the body's gravity-force must push.  (I'm shakier on this than on 
the Greek thinking.)

Dave

*******
Tom McCarthy writes:

> > From Jerry and Donald's responses, it seems that the aerodynamics of the
> objects determines whether the results are more like Aristotle's contention
> or Galileo's.  This leads to another question.  It seems Aristotle did not
> have any idea what air resistance was in the sense of being a disrupting
> force that could be removed from the situation to show gravity's true
> behavior.  Does anyone know if the Greek mindset was one where the
> air/gravity were considered an integrated reality or that there were really
> two forces at work, gravity and air resistance?
>
>
> Tom McCarthy
> Saint Edward's School
> 1895 St. Edward's Drive
> Vero Beach, FL  32963
> 561-231-4136
> Physics and Astronomy


David J. Hamilton, Ed.D.          *  And gladly woulde he learn,
Portland Public Schools           *  and gladly teche.
djhamil@teleport.com              *        - Chaucer