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 AA08153; Tue, 29 Aug 1995 11:09:22 -0700 Return-Path: <westes@usc.com-DeleteThis> Received: from netcomsv.netcom.com (uucp6.netcom.com) by hplms26.hpl.hp.com with ESMTP ($Revision: 1.36.108.11 $/15.5+ECS 3.3+HPL1.1S) id AA039259832; Tue, 29 Aug 1995 11:10:32 -0700 Received: by netcomsv.netcom.com with UUCP (8.6.12/SMI-4.1) id KAA04000; Tue, 29 Aug 1995 10:55:34 -0700 Received: by usc.com (NX5.67d/NX3.0M) id AA08752; Tue, 29 Aug 95 10:10:11 -0700 From: Will Estes <westes@usc.com-DeleteThis> Message-Id: <9508291710.AA08752@usc.com-DeleteThis> Subject: Re: WIND_TALK digest 64 To: wind_talk@opus.hpl.hp.com-DeleteThis Date: Tue, 29 Aug 1995 10:10:11 -0700 (PDT) In-Reply-To: <9508291642.AA08071@cds735> from "Rob Garneau" at Aug 29, 95 09:46:05 am X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 2127
'Rob Garneau says:'
> > Think of the tides as very long period waves. This tidal wave emanates
> > from a node somewhere between Mexico and Hawaii and travels northward toward
> > us.
>
> Since the sun rises in the East, the earth rotates counterclockwise if looking
> at it from the north pole, and the tides are caused by gravitational pull
> of the sun and moon, it seems like the tidal waves should be moving towards
> the west. How do you explain the reversal of direction here?
You know, what I really like about this windsurfer list is that it gives me a
chance to polish up on my college physics courses. :)
Regarding waves resulting from rotation of the earth: the kind of
force you are thinking about would happen only if the earth was
not rotating at all, then suddenly started to rotate. The forces due
to the acceleration would exert horizontal force on the water.
But the earth is not standing still. It is presumably rotating at
more or less a constant velocity. Therefore there is no acceleration
force that moves in a horizontal vector to the surface of the ocean.
There is probably a centrifugal force of rotation, which moves
vertically to the ocean's surface, from the center of the earth moving
out. But these forces are constant, so I don't see how they could
account for tidal action.
Tides are caused primarily by gravity of other large objects that are
near the earth. The best way to think about this is that the ocean
is like a giant tarp with strings attached to it. As the moon gets
closer to the ocean's surface, it is like someone pulling up on the
strings. That's why people are using the spring analogy: the force
is coming from directly above the water, like a hand holding a spring,
moving the hand up or down.
Anyway, I'll let the scientists here correct my imprecise
descriptions. I'm sure I have some of the particulars a little fuzzy.
--
Will Estes U.S. Computer
Internet: westes@usc.com-DeleteThis POB 3150
Saratoga, CA 95070
FAX: 408-446-1013
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