A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

tide and moon question



 
 
Thread Tools Display Modes
  #1  
Old February 13th 07, 07:31 PM posted to sci.astro
[email protected]
external usenet poster
 
Posts: 1
Default tide and moon question

Can someone please explain why the gravity of the moon (which passes
over our beach once a day) causes two high tides per day? Is it due to
the natural frequency of the combined large bodies of water being approx
double the frequency of the moon's appearance? Or is it something else?

  #2  
Old February 13th 07, 08:11 PM posted to sci.astro
dlzc
external usenet poster
 
Posts: 1,426
Default tide and moon question

On Feb 13, 11:31 am, wrote:
Can someone please explain why the gravity of the moon
(which passes over our beach once a day) causes two
high tides per day? Is it due to the natural frequency of
the combined large bodies of water being approx double
the frequency of the moon's appearance? Or is it
something else?


More than one way to look at this. Consider "chunks" of water on the
Earth, looking down on the North pole, with Moon at 12:00. The chunks
at 12:00 and 6:00 have the Moon acting in concert with Earth, the
"lines of action" are parallel. The chunks at 3:00 and 9:00 are free
to move towards/away from the Moon, because they are not getting (very
much) farther from the Earth by doing so. So for a lowest harmonic
solution with two minima (3:00 and 9:00), yields two maxima. Of
course this is only sloppy, so...

http://en.wikipedia.org/wiki/Tide
.... down to Tidal Physics

David A. Smith

  #3  
Old February 14th 07, 12:30 AM posted to sci.astro
Prai Jei
external usenet poster
 
Posts: 42
Default tide and moon question

dlzc (or somebody else of the same name) wrote thusly in message
.com:

On Feb 13, 11:31 am, wrote:
Can someone please explain why the gravity of the moon
(which passes over our beach once a day) causes two
high tides per day? Is it due to the natural frequency of
the combined large bodies of water being approx double
the frequency of the moon's appearance? Or is it
something else?


More than one way to look at this. Consider "chunks" of water on the
Earth, looking down on the North pole, with Moon at 12:00. The chunks
at 12:00 and 6:00 have the Moon acting in concert with Earth, the
"lines of action" are parallel. The chunks at 3:00 and 9:00 are free
to move towards/away from the Moon, because they are not getting (very
much) farther from the Earth by doing so. So for a lowest harmonic
solution with two minima (3:00 and 9:00), yields two maxima. Of
course this is only sloppy, so...

http://en.wikipedia.org/wiki/Tide
... down to Tidal Physics

David A. Smith


OK, now could somebody explain why the time of high tide varies so much with
longitude e.g. six hours between Cardiff and London despite the longitude
difference being only about 4 degrees so moonrise is only about 15 minutes
later in Cardiff than in London.
--
Terms and conditions apply. Batteries not included. Subject to status.
Contains moderate language. Always read the label. Keep out of children.

Interchange the alphabetic letter groups to reply
  #4  
Old February 14th 07, 01:42 AM posted to sci.astro
Llanzlan Klazmon the 15th
external usenet poster
 
Posts: 275
Default tide and moon question

Prai Jei wrote in
:

dlzc (or somebody else of the same name) wrote thusly in message
.com:

On Feb 13, 11:31 am, wrote:
Can someone please explain why the gravity of the moon
(which passes over our beach once a day) causes two
high tides per day? Is it due to the natural frequency of
the combined large bodies of water being approx double
the frequency of the moon's appearance? Or is it
something else?


More than one way to look at this. Consider "chunks" of water on the
Earth, looking down on the North pole, with Moon at 12:00. The chunks
at 12:00 and 6:00 have the Moon acting in concert with Earth, the
"lines of action" are parallel. The chunks at 3:00 and 9:00 are free
to move towards/away from the Moon, because they are not getting (very
much) farther from the Earth by doing so. So for a lowest harmonic
solution with two minima (3:00 and 9:00), yields two maxima. Of
course this is only sloppy, so...

http://en.wikipedia.org/wiki/Tide
... down to Tidal Physics

David A. Smith


OK, now could somebody explain why the time of high tide varies so much
with longitude e.g. six hours between Cardiff and London despite the
longitude difference being only about 4 degrees so moonrise is only
about 15 minutes later in Cardiff than in London.


This is explained in the wiki article cited by David in the port you
replied to.

Klazmon.

  #5  
Old February 14th 07, 07:09 AM posted to sci.astro
Androcles
external usenet poster
 
Posts: 260
Default tide and moon question


"Prai Jei" wrote in message ...
dlzc (or somebody else of the same name) wrote thusly in message
.com:

On Feb 13, 11:31 am, wrote:
Can someone please explain why the gravity of the moon
(which passes over our beach once a day) causes two
high tides per day? Is it due to the natural frequency of
the combined large bodies of water being approx double
the frequency of the moon's appearance? Or is it
something else?


More than one way to look at this. Consider "chunks" of water on the
Earth, looking down on the North pole, with Moon at 12:00. The chunks
at 12:00 and 6:00 have the Moon acting in concert with Earth, the
"lines of action" are parallel. The chunks at 3:00 and 9:00 are free
to move towards/away from the Moon, because they are not getting (very
much) farther from the Earth by doing so. So for a lowest harmonic
solution with two minima (3:00 and 9:00), yields two maxima. Of
course this is only sloppy, so...

http://en.wikipedia.org/wiki/Tide
... down to Tidal Physics

David A. Smith


OK, now could somebody explain why the time of high tide varies so much with
longitude e.g. six hours between Cardiff and London despite the longitude
difference being only about 4 degrees so moonrise is only about 15 minutes
later in Cardiff than in London.


The same reason the tidal range is high in the Bay of Fundy and the Bristol
Channel and low in the Gulf of Mexico and Mediterranean: water sloshes
around in the tub.
The English Channel gets a rise from the Atlantic and then another
from the North Sea, it takes time to move the water in and out.
Here's the proof:
http://www.youtube.com/watch?v=8fu1H1h5SRk





  #7  
Old February 14th 07, 02:57 PM posted to sci.astro
Dr J R Stockton[_10_]
external usenet poster
 
Posts: 3
Default tide and moon question

In sci.astro message .
com, Tue, 13 Feb 2007 11:11:37, dlzc posted:
On Feb 13, 11:31 am, wrote:
Can someone please explain why the gravity of the moon
(which passes over our beach once a day) causes two
high tides per day? Is it due to the natural frequency of
the combined large bodies of water being approx double
the frequency of the moon's appearance? Or is it
something else?


More than one way to look at this. Consider "chunks" of water on the
Earth, looking down on the North pole, with Moon at 12:00. The chunks
at 12:00 and 6:00 have the Moon acting in concert with Earth, the
"lines of action" are parallel. The chunks at 3:00 and 9:00 are free
to move towards/away from the Moon, because they are not getting (very
much) farther from the Earth by doing so. So for a lowest harmonic
solution with two minima (3:00 and 9:00), yields two maxima. Of
course this is only sloppy, so...


I would not call it sloppy; I'd call it just plain half-wrong.

http://en.wikipedia.org/wiki/Tide
... down to Tidal Physics


That's OK but longwinded.


Sea-tides are mainly caused by the lunar gravity gradient (with a
significant component from the solar).

The sea facing the Moon (being nearer) is attracted by the Moon more
strongly than is the Earth as a whole, and the sea on the farther side
is attracted less strongly than is the Earth as a whole. The sea
therefore rises in two areas, under the Moon and opposite it; and falls
in between.

--
(c) John Stockton, Surrey, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
 




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

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tide out on Titan? A soft solid surface for Huygens (Forwarded) Andrew Yee News 0 December 1st 05 06:30 AM
Tide out on Titan? A soft solid surface for Huygens (Forwarded) Andrew Yee Astronomy Misc 0 November 30th 05 10:34 PM
moon on meridian high tide WGTN NZ (casio fish n tide watch.) Don McDonald Misc 1 January 21st 05 05:13 AM
Looking for tide calculation algorithm Chuck S. Astronomy Misc 5 October 11th 03 01:53 PM


All times are GMT +1. The time now is 12:33 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.