Re: [Paddlewise] One bright thing pre Y2K (tides)

From: Alex Ferguson <a.ferguson_at_chem.canterbury.ac.nz>
Date: Tue, 21 Dec 1999 09:30:00 +1300
At 05:41 pm Bob Myers 16/12/99 -0800, you wrote:

>Matt,
>
>You don't understand tides in the least if you believe this.
>
>Consider the question: why are there 2 lunar tidal bulges,
>one on each side of the Earth?  If it's just simple matter of the 
>Moon "pulling" on one side, why the bulge on the opposite side?
>Tides are usually every 12 hours, not every 24. 

Except the places where there is one tide every 24 hours. Personally I
think the "slosh" effect is the best term and/or way of visualising these
abberations. A shallow tray with the opposite ends being alternatively
lifted to get the water to slosh back and forth. Dependant on the natural
cyle, the "tuning" of the length of the tray versus the timing of the
gravitational tides as to whether and what happens. The diagrams in books
so often conveniently forget that there are continents, bays and islands
complicating the whole thing. Around our bit of coast, about 300 miles of
it there is only one spring tide a month and the tidal heights each day
make a very ragged graph. 

Nothing is quite that simple if you want to get down to definitive causes.
There are 3 major causes and a mass of minor ones if you want to calculate
actual times and heights.

NIWA have a good WEB site with movies of tides, I'll track it down if
anyone is interested.

>And please take your spurious earthquake prediction speculations
>to some place where it is on topic.  This is not the right
>forum to discuss this, even if there was the slightest merit
>to your uninformed suggestions.

Very good series on TV at the moment, "The Planets", you should see what
gravitational effects do to some of the moons around planets in the solar
system!!!

Alex
.
.
Alex (Sandy) Ferguson
Chemistry Department
University of Canterbury
New Zealand
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Received on Mon Dec 20 1999 - 12:28:19 PST

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