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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? |
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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 |
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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 |
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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. |
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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 |
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tide and moon question
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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. |
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