Re: Thermo of Springs/Sidebar

[brian whatcott <inet@INTELLISYS.NET>]

At 14:31 11/25/99 -0700, Jim Green wrote:

> > > ///my question is whether there is _any_ example of a macroscopic
> > > reversible process other than the ideal piston in a cylinder.
> >
> > This is another way of asking if there is an 100% efficient machine.
> >  A question that came up a few weeks ago. Steel on ice or ptfe
> > and ball bearing races come to mind, then fluid and air bearings.
>
> Brian, I could use more help here. In what way are these examples of near
> frictionless processes thermodynamically reversible???

..er...Jim, you asked for macroscopic reversible processes.
There's your question, look up to the second and third lines.

So that a vehicle could descend a valley and nearly recover its
altitude on the other slope, if carried on ball races?

> And BTW what is meant by "ptfe"?

Polytetrafluoroethylene is better known in the US by trade names
 such as teflon. A low friction plastic.

> > But the celestial spheres seemed almost dissipationless - at least
> > on human timescales.
>
> Ditto.

Tidal effects were the only easily visualized effect -
crustal or liquid.

> > A gas tight piston in a smooth cylinder would
> > come last, I suppose, on any rational list!
>
> We, the irrational, need more help.
>
> Jim Green

Try pushing a well fitting piston with rings down an oily cylinder.
 This is what I think of as a dissipating process.
     Of course a thermodynamicist might think differently.   :-)




brian whatcott <inet@intellisys.net>
Altus OK