Sometimes when I post I feel like the "Samuel F. B. Morse" of MAD
magazine fame:

"What hath got wrought?"

On Tue, 02 Apr 2013 10:19:41 -0400, Ed Huntress wrote:
On Tue, 02 Apr 2013 06:56:24 -0500, Frnak McKenney
wrote:

[...]

So... the implication is that "performance" here implies "time", much
like charging a capacitor. Hooking a capacitor across a battery with
voltage "V" will eventually charge the capacitor to "V"; putting a
resistor in series with the capacitor won't affect the final potential
across the capacitor: it will still eventually reach V. However, it
may take longer... perhaps a _lot_ longer. grin!

Right.

Makes sense: If I have a "vacuum-formed plastic object" production
line, I probably care whether it takes minutes, hours, or days for the
vacuum at the mold to reach the right level. Or am I missing
something?

The vacuum-forming rigs I've seen have to pull full vauum within
seconds, or the plastic would be too far from the heating element for
the thing to work. ...

Eureka! ( Which is apparently Greek for "A minor crack in my otherwise
impermeable wall of ignorance is dimly illuminating the back of the
cave." grin! ) "Flow". "Rate".

... So I have some trouble relating to your example.

Sorry. After reading the folowups I think I can clarify ( famous last
word! ) the source of my confusion. I had been reading all the
references to "vacuum" and interpreting them as "end-state air
pressure", a static value vaguely analogous to the end-state potential
across a capacitor in a DC circuit. Depending on the circuit
resistance, the capacitance, and the potential feeding the circuit
this can take femtoseconds or gigayears ( though the latter doesn't
seem all that useful grin! ).

However, it looks like we're all saying much the same thing in
different ways. The effect of hose length on any vacuum system
depends on how much air you're pulling through it. If the flow rate
is very low -- for example, if you're just dealing with the slow
leak in a good vacuum-cure composite bag -- then hose length matters
little. If you're trying to vacuum the dirt off of your kitchen
floor, which requires a very high flow rate, the longer hose
presents more friction to the air flow and reduces the vacuum
reading you would get, if you measured it, at the terminal end of
the hose.

Agreed; an analogous electronic circuit would have a lot of leakage
over, under, around, or through something. grin!

My apologies to all for the distraction from the subject at hand.


Frank
--
It's not what we don't know that gives us trouble, it's what
we know that ain't so. -- Will Rogers
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney aatt mindspring ddoott com