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

[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.
>
> Help!
>
> 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 applies
  force through a similar distance: but then wait, the nth link applies
  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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