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From: yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille)
Newsgroups: rec.skydiving
Subject: Re: Graph of osc'n due to high windforce
Message-ID: <1000@lhdsy1.chevron.com>
Date: 25 Jun 91 20:39:33 GMT
References: <1991Jun18.150541.5220@rodan.acs.syr.edu> <983@lhdsy1.chevron.com> <1991Jun24.153922.12763@rodan.acs.syr.edu>
Organization: Chevron Oil Field Research, La Habra, CA.
Lines: 49

In article <1991Jun24.153922.12763@rodan.acs.syr.edu> greeny@top.cis.syr.edu (Jonathan Greenfield) writes:
>In article <983@lhdsy1.chevron.com> yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) writes:
>>No, you are wrong about the potential energy *not* being transformed
>>into kinetic energy. A simple answer to that is "The Law of
>>Conservation of Energy". A more physical answer is: the reason why the
>>velocity is terminal is due to friction with the atmosphere. The
>>potential energy is being transformed in kinetic energy which, in turns,
>>is transfered as heat due to the skydiver "frictionning" with the
>>atmosphere! What happens is that the skydiver gives up the *kinetic*
>>energy, not the potential energy, because it is first transfered to
>>kinetic, then heat.
>
>I disagree.  Of course energy is conserved--but in the system (diver +
>atmosphere), not just in the diver.  As I stated in a previous post, the 
>potential energy is lost via drag to heat, sound, etc.  However, it cannot
>be that the energy is first transformed into the skydiver's own kinetic energy.
>As long as the diver's velocity is fixed, he cannot be gaining any kinetic
>energy (KE = 0.5*mass*velocity^2).  Molecules in the atmosphere, of course, 
>can gain kinetic energy.
>
I strongly disagree and let see if I can make you change your mind.
In the absence of atmosphere, the potential energy (of a falling object)
would be changed into kinetic energy. Do you agree?
If so, then, since the atmosphere does not "know" that a body is there,
how could the mere presence of an atmosphere change the laws of physics?
How could the potential energy of the falling object suddenly stop being
transferred into kinetic energy and instead change to be transferred
into heat? (well, according to your model, the potential energy would
gradually transfer itself from kinetic to heat, as "terminal" velocity
would be reached.) I just don't see a law of physics that would allow
that.
Also, if the potential energy was not transformed into kinetic energy
(or stopped being transformed into kinetic energy and instead transfered
itself into heat) then the skydiver would slow down due to the friction
with the atmosphere. He/she does not because of the potential energy
(he/she is still above ground) that is still there.
The diver's velocity is fixed (say) so he/she is not gaining any kinetic
energy, but he/she is transfering it.

...deleted text...
>assumption.  Maybe I'm too used to feeling that 1 g upward acceleration under
>my feet every day. :)

Really? Are you feeling 1 g all the times? (or are you just kidding?) ;-)
-- 
  Philip Yzarn de Louraille                 Internet: yzarn@chevron.com
  Research Support Division                 Unix & Open Systems
  Chevron Information & Technology Co.      Tel: (213) 694-9232
  P.O. Box 446, La Habra, CA 90633-0446     Fax: (213) 694-7709