The Straight Dope

Go Back   Straight Dope Message Board > Main > General Questions

Reply
 
Thread Tools Display Modes
  #1  
Old 10-26-2008, 05:16 PM
pseudotriton ruber ruber pseudotriton ruber ruber is offline
BANNED
 
Join Date: Sep 2002
Location: Outer Control
Posts: 10,394
How fast does the tide move?

Not in and out, but up (or down) the coastline? There are various times given for high and low tides all along Long Island, and I presume there's some rhyme or reason to it, though this tides chart doesn't seem to suggest any real pattern offhand. Is there some pattern I'm not seeing based on geography generally, or is it all a matter of factors others than geography (depth of bay, the mood that Poseidon is in that morning, stuff like that).

If you want a specific inquiry, when I go running on the beach I often choose the direction I run in so I won't be staring straight into the sun as I run, but I've been wondering if the low tide could be moving along the shoreline with me, or against me, and if so, how quickly--much faster than I run, much slower, etc. or whether this is impossible to predict on a regular basis.

Last edited by pseudotriton ruber ruber; 10-26-2008 at 05:16 PM.. Reason: fix'd link
Reply With Quote
Advertisements  
  #2  
Old 10-26-2008, 05:41 PM
sailor sailor is offline
Guest
 
Join Date: Mar 2000
Every location is different. The attraction of Moon and Sun are only the primary forces which cause the tides but then the water is like water sloshing around in a pan and no general rule can be made. Only specific rules for specific places.

Take the Chesapeake bay. It runs from N to S and the primary tidal forces would pretty much cross at right angles. If it were a lake there would be no appreciable tides. But at the mouth there are tides which create tidal waves which progress up the Chesapeake. So the tides on the Chesapeake are not directly caused by any attraction of the moon but by a wave at the mouth which then moves up the bay (and reflects etc.).

Depending on the shape of the bay or inlet the tidal wave can reinforce and the tide level difference can be great. This is what happens in the bay of Fundy.
Reply With Quote
  #3  
Old 10-26-2008, 09:36 PM
Napier Napier is offline
Charter Member
 
Join Date: Jan 2001
Location: Mid Atlantic, USA
Posts: 7,764
Ditto sailor. There is a major tidal effect that is, I think, a couple feet in size that runs around the earth every 24 hours (more precisely there is a bigger effect from the Moon that takes something like 25 hours and a smaller effect that is 24 hours from the Sun). However, in many places on the coast there are sloshes or echos or resonances that are much bigger, and how their timing relates to the open ocean tides depends strongly on the local geography. Broadly speaking, there is a whole category of these that are in sounds that communicate with the open ocean only through a few small inlets, and the big effect this geometry has is to make the tides in the sounds be smaller and lag behind the open ocean tides. There is also a tide of about half a foot in the continents, if I remember right, because the crust shifts up and down. Of course, there's nothing to compare it to, like you can compare the bigger tides on water to the relatively more stationary land.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 01:48 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@chicagoreader.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Publishers - interested in subscribing to the Straight Dope?
Write to: sdsubscriptions@chicagoreader.com.

Copyright 2013 Sun-Times Media, LLC.