Received: from hplms26.hpl.hp.com by opus.hpl.hp.com with SMTP (1.37.109.8/15.5+ECS 3.3+HPL1.1) id AA26135; Fri, 25 Aug 1995 14:11:02 -0700 Return-Path: <shred@netcom.com-DeleteThis> Received: from netcom13.netcom.com by hplms26.hpl.hp.com with ESMTP ($Revision: 1.36.108.11 $/15.5+ECS 3.3+HPL1.1S) id AA000545128; Fri, 25 Aug 1995 14:12:08 -0700 Received: by netcom13.netcom.com (8.6.12/Netcom) id NAA23746; Fri, 25 Aug 1995 13:53:30 -0700 Date: Fri, 25 Aug 1995 13:53:22 -0700 (PDT) From: "Edward W. Scott" <shred@netcom.com-DeleteThis> Subject: Re: Re[2]: WIND_TALK digest 63 To: wind_talk@opus.hpl.hp.com-DeleteThis In-Reply-To: <03e1abd0@ccsmtp.wj.com-DeleteThis> Message-Id: <Pine.3.89.9508251335.A21237-0100000@netcom13> Content-Type: TEXT/PLAIN; charset=US-ASCII
Thanks Geoff, being a software guy by training, that's what I think of
too. My over-simplified model of the Bay would include three jugs
connnected by pipes. Jug 1 is the Pacific, Jug 2 is the Bay, and Jug 3 is
the Sacramento River. The pipe between jugs 1 and 2 is the Golden Gate,
and the pipe between jugs 2 and 3 is the Carquinez Straits. The only one
that changes independently (a tap is filling, or a hole in the jug is
draining) would be jug 1 (cause it's so huge) which drives jugs 2 and 3
(forget Sierra run-off). Because the pipes cause flow resistance between
each of the jugs, there'll be times when the level remains the same in a
jug (high or low tide) but the current of water is still flowing between
jugs (e.g. ebbing or flooding).
The model is really much more complex because both the Sacramento and the
Bay are long and when current is flowing in at one end, it actually may be
slack or ebbing at the other end (a transmission delay, something the EE
Enginerds have been talking about). I think we need Mr. Wizard or Dr.
Science here (I have a Master's Degree, in Science!).
Feel free to flame if this is wrong.
-shrEd
Ed Scott
shred@netcom.com-DeleteThis
On Fri, 25 Aug 1995 Geoffrey.Boehm@wj.com-DeleteThis wrote:
> When I studied electricity in school, the favorite analogy was to
> think of it as water flowing through a pipe - voltage was water
> pressure, current was water flow etc. This was a reasonable approach
> because most students had a lot more experience with water than
> electricity, and water is both less abstract and more visible.
>
> How ironic that there are actually windsurfers who find electrical
> objects more intuitive than water. Only in silicon valley.
>
>
> ______________________________ Reply Separator _________________________________
> Subject: Re: WIND_TALK digest 63
> Author: James.Paugh@Eng.Sun.COM-DeleteThis (Jim Paugh) at INTERNET
> Date: 8/25/95 11:17 AM
>
>
> Jim Paugh asks:
>
> > "What I would like to hear is an explanation of why slack current occurs
> > after say, a low tide. For instance, today, low tide at Crissy is at
> > 5:03pm, but low slack is at 7:29pm! How is it that slack current occurs
> > 2.5 hours after low tide? "
>
> Will Estes writes:
>
> > The best explanation I have heard on this was Ken Poulton's a few
> > months ago on the wind_talk list. He compared tidal dynamics to
> > electron flow within a wire. At the outside, resistance to the flow
> > is greater than in the middle. So at the point where the flow stops
> > on the outside, the flow is still moving at the center.
> >
> > Consider the analogy to the Bay: at the edges we have relatively
> > shallow mud flats that offer a lot of resistance to the current. In
> > the center you have a deep shipping channel where the water flows more
> > freely. So at the low tide, the resistance of the mud flats on the
> > edges just matches the current flow, and you have a zero current at the
> > edge. But in the middle of the channel the ebb is still continuing,
> > and it doesn't stop until a later time, because there is less
> > resistance to stop the outward flow.
>
> Kirk Lindstrum writes:
>
> > It has to do with the shape of the bay. If you are an EE, then you can
> > model the bay as a bunch of capacitors in each big, deep section and
> > each "straight" as an inductor with the largest inductor at the Golden
> > Gate. The "system" is driven by tide height (Voltage input) at the
> > Golden Gate. Voltage is the same as tide height and current is the same for
> > both with one being water and the other electrons.
>
> Oh, NO! The dreaded EE analogy! Picture a blank stare on my face, eyes
> glazed over, mouth agape :^o
>
> Thanks guys, for trying, but I think I'll stick to the tidal wave rolling
> through the Golden Gate analogy!
>
> ~Jim
>
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