Re: [Phys-l] Work done by Static Friction

[Brian Whatcott <betwys1@sbcglobal.net>]

I was bemused by all the consternation,  the delicate tap-dancing
and the  curious mix of self-congratulation   for doing physics that
 I read in this thread,   when upon reading Rick's note below  I
 realized the issue.
 This seems to be a difficulty arising from the use of a particular
 model,   in a case  which "does not simply follow the rule".

Sure static friction can allow a part to speed up on a truck bed. And a
bolt and nut can allow another truck part to speed up with the rest
 of the bits.
And sure, these fixings and forces of adhesion  can apply a force.
Moreover, if there is a structural member involved, the one end of it can
 apply a force to the other end of that steel strip.

But I don't typically think of half a strip of steel doing work on its
other half. There is no relative movement to satisfy the conditions
 for the "work" model.

But hang on a darn minute:   wasn't I writing in the last day or two that
 an engine does work on a drive shaft? And so on, as far as the wheel/tire?
Would it be any more satisfying if I said instead that the engine passes
energy to the transmission, drive shaft, differential etc.?
That energy flows through these components?   Like I sometimes talk
 about heat flowing though a conductive strip?   That's Jim territory,
and I easily see it is contentious.

Brian Whatcott

At 06:52 AM 3/16/2007, you wrote:
> No time to look this up (64 papers to grade), but I seem to recall that one
> can preserve the Work/Energy theorem in this case if one looks at what is
> happening microscopically?  Maybe akin to the fact that any horizontal
> surface must deform slightly to hold up a mass placed on that surface?  Just
> wondering.
>
> Rick  [Who really doesn't have a problem with the fixed observer saying that
> static friction is the force that causes the displacement of the crate.]
>
> ----- Original Message -----
> From: <carmelo@pacific.net.sg>
>
> Some physicists proposed that 'static friction' to be
> named "shear adhesion" instead. You may consider transfer of "Coulomb
> energy" from the microscopic view?
>
> Alphonsus


Brian Whatcott    Altus OK    Eureka!