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In lugnet.off-topic.fun, Richie Dulin wrote:
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It’s like a pendulum, I guess, but in space (which is where the earth is),
there’s no friction, so it just keeps going - backward and forward ad
infinitum.
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Pendulums don’t work in the absence of gravity, and they really only work with
the largest gravitic pull from their location, whether it be from a single
source or closely clustered combined sources. The moon exerts the largest
gravitic pull on Earth, but the sun influences tides just as surely as the moon
does (which is how we get “spring” and “neap” tides).
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The sea monkey explanation was a good one too, just not the right one. IMO.
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Neither is yours, but the Sea Monkey explanation was at least funny. Every body
of matter (even a single atom) has a gravitic pull that it exerts on every other
body of matter. The moon’s gravity pulls at the water on earth the most, but
the sun still has about half as much effect as the moon (gravity is reduced over
distance), which is why the absolute highest possible tides are achieved
directly under a full solar or lunar eclipse (gravity from both sun and moon
combining), and the lowest possible tides occur at 90 degrees to an eclipse
(because the super high tides are pulling more water away from the low-tide
areas).
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The energy from the moon’s initial stopping started the tides! (You don’t
think pendula just start, do you? That would be crazy!)
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Actually, the inertial drag from the tides is much more likely to have caused
the moon to settle into a 1 day-per-year rotation. If you don’t believe me,
check this page. It is
entirely possible that the moon arrived with just the right amount of rotation
to produce a 1:1 day/year cycle, but highly unlikely. The mere presence of the
moon (and the sun) is what causes the tides in the first place. Here’s one that
will blow your mind: given enough time, Earth’s day will slow down enough to
exactly match that of the moon, the same surfaces will always point towards each
other, and significant tidal fluctuation will only be caused by the sun (since
the lunar “tide” will be locked into place based on what part of Earth is
directly under the moon). Of course, none of us will still be around to witness
this spectacle, and indeed the sun might evolve into a red giant before the
earth can stop spinning (in which case, noone will get to witness it, because
the sun will engulf Earth’s orbit). If you want to read up on “tidal coupling”,
go here.
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No wasted energy, because there’s no friction in space!
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But there is on Earth. Where the tides occur. And there is between water
molecules. Which is what the most noticable tides involve (though even Earth’s
crust fluctuates a tiny bit due to tidal influences). And gravitational drag
can have very similar effects to friction on a rotating body, and you better
believe there’s some of that going on between Earth and Luna.
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Exactly. The earth spins, but does not explode. The moon does not spin, but
does not explode because of the tides.
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The moon does indeed spin (one lunar day per lunar year), and tides have nothing
to do with it not exploding. Venus takes
243 Earth-days to complete
one single axial rotation, and it doesn’t explode. I think you’ve either been
the victim of a heavy dose of leg-pulling, or you’ve been taking science lessons
from someone with more imagination than education.
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All revolving bodies explode if you stop them from moving, so the moon
really, really wants to explode.... it’s just that the energy from the
rotation went into the earth’s tides rather than the explosion.
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They only have problems if you bring them to an abrupt stop, and that’s probably
mostly when dealing with planets/moons that have liquid cores that will resist
any rotational change to the planetary/lunar crust. Our moon is one solid hunk
of rock (and quite small), and should weather an abrupt change much more easily
than our planet would.
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That’s easy to explain - the oceans did not entirely freeze in the ice ages
we’ve already had (I said “if we get another ice age here on earch, and the
oceans freeze note the added emphasis).
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An ice age that results in frozen oceans would be more likely to cause physical
harm to Earth than the moon, as the oceans would be unable to flex with the
tide. Fortunately, the tides themselves should do a good enough job of
preventing the oceans from ever freezing solid, barring any catastrophic events
like Earth being bumped out of its orbit (and if that happens, I doubt any of us
would still be around long enough to enjoy ice-skating in the middle of the
Pacific Ocean).
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Message has 1 Reply:
Message is in Reply To:
 | | Re: The Derotatinator
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| (...) It's like a pendulum, I guess, but in space (which is where the earth is), there's no friction, so it just keeps going - backward and forward ad infinitum. The sea monkey explanation was a good one too, just not the right one. IMO. (...) The (...) (21 years ago, 22-Jun-03, to lugnet.off-topic.fun, lugnet.off-topic.geek, lugnet.space, FTX)
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