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Re: Friction



Hi John,
1) The two surfaces may indeed have different coefficients of
friction (different "polish" with more or less points of contact, the
effect of an "uneven" weight distribution, weight effect shift due to a
higher center of gravity, etc.)
2) The statement that the coefficient of friction is independent of
area is a "rule of thumb" empirical statement, not to be taken as a
"gospel law of nature". "All things being equal", under "ordinary"
circumstances, you should find it to be a workable approximation. Take
measurements - how different are the mu values?

-Bob

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor
-----Original Message-----
From: John DaCorte <jdacorte@mdihs.u98.k12.me.us>
To: PHYS-L List <phys-l@atlantis.uwf.edu>
Date: Thursday, October 29, 1998 10:40 AM
Subject: Friction


Hi,

I was wondering if someone could help me with a demonstration I have had
trouble with. I place a block of wood on a tilted desk and tilt it to
the angle that just makes the block move and secure the desk. Then I
put
the block on another edge (with a different surface area) to show that
the
frictional force and the coefficient of friction do not change with
surface area. The problem is that the block always stays put on the
side
with the large surface area and slides on the side with the small
surface
area. Any explanations? Thanks in adavance for any help.

John DaCorte