What Are Love Numbers and How Do They Impact Tidal Deformations?

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Discussion Overview

The discussion centers on the concept of tidal deformations, specifically exploring the role of Love numbers and their impact on the Earth's rotation and tidal interactions. Participants examine the mechanics behind tidal forces, the effects of the Moon's gravity, and the implications for various Earth components, including the atmosphere and solid body interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the tidal bulge is influenced by the Earth's rotation and the Moon's gravity, leading to a slowing of the Earth's rotation, but seeks clarification on the mechanics behind this.
  • Another participant claims that the Earth's rotation is speeding up due to the redistribution of mass from dams, which is challenged by others who assert that this is incorrect.
  • It is noted that the Moon's gravity causes tidal friction, which slows the Earth's rotation and leads to the Moon's gradual recession from the Earth.
  • A participant questions whether tidal interactions occur with the atmosphere and mantle, suggesting that while the atmosphere is affected, the impact is smaller compared to ocean tides.
  • Discussion includes the idea that tidal interactions may not occur between hypothetical 100% solid bodies, with one participant asserting that rigid bodies would not exhibit tidal braking due to the absence of a tidal bulge.
  • Another participant mentions that there are indeed tides in the solid part of the Earth, citing the need for adjustments in the LHC at CERN due to tidal effects on the ring geometry.
  • Reference to Love numbers is made, indicating that they are relevant to understanding tidal deformations and that varying degrees of tidal interactions depend on the composition of different Earth layers.

Areas of Agreement / Disagreement

Participants express differing views on the current state of the Earth's rotation, with some asserting it is slowing while others claim it is speeding up. The discussion remains unresolved regarding the specific mechanics of tidal interactions and the implications for solid bodies.

Contextual Notes

There are limitations in the discussion regarding assumptions about the rigidity of bodies and the extent of tidal interactions, as well as the dependence on definitions of tidal effects across different Earth components.

Hoophy
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So I THINK I understand that the tidal bulge is resting slightly in front of the moon because of the Earths rotation and the moons gravity, it pulls the moon 'forward' a little adding energy to the moons orbit and expanding it, what I do not understand is why the Earths rotation is slowing. I think I understand that it the energy of the tides (And also tidal electricity generation) has to come from somewhere. Could somebody please explain to me why mechanically the Earth's orbit slows down? Also do these tidal interactions occur with the atmosphere and mantle? Can these tidal interactions occur between hypothetical 100% solid bodies, if so to what extent? Also if my original assumptions are wrong please let me know, as I know you will. Thank you for your time. :)
 
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Last I heard, the Earth's rotation was speeding up. This was due to dams holding large bodies of water at high latitudes, thus bringing more of the Earth's mass towards the center.
 
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The moon has a braking effect on Earth's rotation due to tidal friction. This also causes the moon to slowly recede from the earth. It will eventually become tidally locked with earth, but, probably not before the sun incinerates it.
 
Algr said:
Last I heard, the Earth's rotation was speeding up. This was due to dams holding large bodies of water at high latitudes, thus bringing more of the Earth's mass towards the center.

dunno where you heard that, but it is incorrect

if what you said was true, we would be taking away leap seconds, not adding them periodicallyDave
 
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Hoophy said:
Could somebody please explain to me why mechanically the Earth's orbit slows down?

The Moon's gravity pulls on the bulges, and the bulges pull on the rest of the Earth. So as the Moon is pulled forward by the leading bulge, the Earth is pulled in the opposite direction, which slows its rotation down.

Hoophy said:
Also do these tidal interactions occur with the atmosphere and mantle?

I'm sure the atmosphere is pulled just like the tides are, it's just that any effect would be much smaller than the tides. As for the mantle, I don't know.

Hoophy said:
Can these tidal interactions occur between hypothetical 100% solid bodies, if so to what extent?

If you mean 100% rigid bodies, then I don't believe so.
 
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There are also tides in the solid part of Earth. The LHC at CERN has to adjust their magnets frequently because the ring geometry changes due to those tides. On a global scale, the Earth is not that solid.
LHC and tides
 
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Here's a pic from a random website showing the interaction Drakkith described:
tidalbraking.jpe


Regarding effects of rigidity on tidal deformations, you might want to look at 'Love numbers'. Googling for the phrase is slightly problematic, for obvious reasons - just make sure you add the keyword 'tides' to your search query.
In short, you don't get tidal braking from a 100% rigid solid, as the tidal potential can't produce a tidal bulge. Since such a thing doesn't exists in reality, you end up with varying degrees of tidal interactions depending on composition - the atmosphere responds differently than the oceans, which differ from the crust, which differ from deeper, denser regions of the planet.
 
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