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The moon is moving further from the Earth. To the extent that after 600 million years we will no longer enjoy full solar eclipses as it will be too far away to completely block the sun.

The reason the moon is moving away is because the Earth's rotation of 1 day is faster than the moon's orbit of about 28 days. The Earth's rotation is slowing as it transfers energy to elevate the moon. A by product of the Earth's tides where the moon drags the water.

Note that while conceptually the Earth is accelerating the moon, this acceleration boosts the moon to a higher orbit and its effectively moving slower as a result of this "acceleration"

I'm pretty sure that if the Earth were solid with no flowing liquids this "tidal leash" would have no effect. Maybe a tiny effect as mountains would be gravitational features.

So that's my question: Am I right that the moon's altitude increase would cease if the Earth didn't have liquid oceans?

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    $\begingroup$ Whats a tidal leash? The same thing as a tide? $\endgroup$ Commented Jun 20 at 13:35
  • $\begingroup$ The tides are caused by the moon's gravity pulling on the sea causing it to bulge slightly at the part of the Earth facing the moon* As the Earth rotates this bulge moves over the surface of the Earth. Equal and opposite, if the mopon pulls this bulge, then this bulge pulls the moon. That's waht I mean by a tidal leash * Gross simplification. To be technical there is a bulge facing the moon as a result of stronger lunar gravity, and away from the moon as a result of string centrifugal force, but this is not relevant to the question $\endgroup$ Commented Jun 20 at 14:34
  • $\begingroup$ Then your argument is flawed since gravitational pull is independent of what it pulls on. So even if the tidal effect (in amplitude) on mountains and other solid matter is smaller, the force acting on the moon is the same. (Barring some effects from the fact matter moves a tiny bit nearer). So no, it shouldnt change of any significance $\endgroup$ Commented Jun 20 at 14:45
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    $\begingroup$ Work cannot be done without force, force can act without work. Also, the force acting on stuff really only depends on distance and mass, so since frozen water is as "heavy" as liquid and neglecting the slight increase in height, the force is the same. Even including friction and whatnot. $\endgroup$ Commented Jun 20 at 14:53
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    $\begingroup$ Two additions: The first is to clarify my first statement: If you hold something up (i.e. you is not necessarily you as a person) you exert force on an object without doing any work. The second concerns the "no work: statement: You do increase some energy, imagine the ice as being springs on molecules. Then the slight stretching of ice is work, given by (a toy model) $1/2 kx^2$. Where $k$ is some spring constant, x the displacement. $\endgroup$ Commented Jun 20 at 14:57

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Am I right that the moon's altitude increase would cease if the Earth didn't have liquid oceans?

It should certainly be less, though it is difficult to test. It would not stop entirely.

The recession of the moon comes from the transfer of orbital kinetic energy to other forms. The ocean tides allow for transfer into the ocean and eventually to heat.

Without the flowing oceans, the landmasses still are stretched and relaxed which generates heat and tidal drag, though to a much smaller extent. We can see this type of energy transfer happen at a much larger rate on Io. Huge amounts of energy move into that moon without the benefit of an oceanic surface.

Hypothetically to stop the recession, you need to not only get rid of the ocean, but make the earth a completely rigid body. Then forces tending to deform the earth would do no work.

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  • $\begingroup$ You're agreeing with me, and disagreeing with the comment above by Confuse-ray30. You're basically saying the moon would be boosted less, and the amount of boost depends on the ability of Earth matter to flex, with ocean being an almost perfect flexer. $\endgroup$ Commented Jun 21 at 5:20

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