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Re: Internal or external?



I always used the two free body approach for solving this problem, but
pointed out that the final result is interpretable as a "system" equation
involving only external forces. However, I hasten to caution that
extrapolating this "system" approach to more involved situations involves
intuitive interpretation, is hazardous and therefore not recommended
except perhaps as a check or further insight into a result already
obtained by sure-footed methods.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, October 08, 1999 2:57 PM
Subject: Re: Internal or external?


The combined mass in the Atwood's machine moves in the
direction of the net force; it can be treated, mathematically,
as if it were moving along an axis. Yes, an axis bending
over a pulley is an abstraction. So what? How do we decide
which abstractions are good and which a bad?
Ludwik Kowalski