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[Phys-L] Re: Quick question on static frictionHi All

The questions at the end of this message need
clarification concerning the purpose of the questions.
Please explain why subdivision is, or is not, necessary
for any practical or theoretical purposes.

Thanks, Herb

On Thu, 10 Mar 2005 11:58:11 -0600 Brian Whatcott <betwys1@SBCGLOBAL.NET>
At 08:55 AM 3/10/2005, you wrote:
Hi All,

I have a quick question related to static friction that came up
in class today - and I just don't have time today to search the
archives - so forgive me if I'm traveling an old path here.

If I place a coffee cup on a sheet of paper and pull on the paper
gently enough to accelerate the coffee cup without it slipping on
the paper, has the force of static friction done work on the
coffee cup? One of the homework problems in Serway (Physics for
Scientists and Engineers) implies that no work is done by the
static frictional force because there is no actual displacement
of the cup relative to the paper. I don't find that very
satisfying because the cup still gains kinetic energy and the
only force acting horizontally on it is the static friction.


Bob at PC

If I connect a chain to a 1 kg mass resting on a table,
and pull the end link so as to move the mass, my hand does work by
applying a force through a distance. But wait, the first link
force through a similar distance: but then wait, the nth link
the same force through a similar distance.

Are ALL the links applying work? That would be cumulative:
but wait: what goes in as plus work at one end of each link,
returns as minus work at the other end of each link.
Or does it? If a connection may sensibly be treated as one
element, is it helpful to subdivide the action?

Brian Whatcott Altus OK Eureka!

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