Re: [Phys-l] Centrifugal redux

[Joseph Bellina <jbellina@saintmarys.edu>]

Let me speak as the spouse of a historian of the philosophy of  
science.  The words we use and the words that are translations of  
Aristotle don't always map easily.  I'm not sure that Aristotle's  
notion of efficient cause, or formal, or material, or final, maps on  
to our notion of force in the way that the quoted reading and  
following commentary might suggest.

joe

Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556

On Apr 2, 2009, at 10:28 AM, Polvani, Donald G. wrote:

> John Clement wrote:
>
> > There was an article, I think in TPT which looked at the Aristotelian
> ideas.
> > Of course one needs a force to keep things going on the Earth,  
> > because
> of friction.  However, he also wrote as I recall a statement to >the
> effect that things would keep going unless stopped by a force.  He  
> came
> close to getting it right.  I remember being surprised at this>  
> piece of
> history, so I am fairly sure I actually read it.
> > Now does anyone remember the actual article?
>
> The following is taken from an explanation of Aristotle's book on
> physics at http://muse.tau.ac.il/museum/galileo/ 
> aristotle's_physics.html
>
>
> "In this book, Aristotle explains the main principles of his natural
> philosophy. The book deals with the subject of motion and its causes,
> the motion of objects from one place to another, and motion as a  
> general
> concept of change of state. According to Aristotle, the motion of
> physical bodies is of two types: natural motion and violent motion."
>
> "Natural motion is the motion arising from the nature of an object.  
> This
> motion does not require an external cause in order to occur. For
> example: Heavy bodies naturally move toward the center of the earth,
> therefore falling is a natural motion. The natural motion of  
> objects is
> one of the characteristics of an object. For example: The natural
> movement of the celestial bodies made of ether is circular (see the
> Ptolemaic planetary system) rather than a movement toward the  
> center of
> the earth."
>
> "Violent motion, by contrast, is motion contrary to the nature of the
> object and requires an external force in order to occur. Most motions
> are of this type. A stone thrown into the air moves in a violent  
> motion,
> against its nature and therefore requires force in order to cause  
> it to
> move. In any discussion of violent motion, one must find the reason  
> (the
> force) which causes this motion, as long as it exists."
>
> So, Aristotle believed that natural motion required no force, but
> violent motion did require a force.
>
> Don Polvani
> Northrop Grumman Corp.
> Undersea Systems
> Annapolis, MD 21404
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