@userLTK -- If you are writing about the Earth's tidal bulge, this (a) would have zero impact on a spherically symmetric Moon and (b) doesn't exist. The Moon, however, does have a frozen tidal bulge.

@DavidHammen I don't believe that tides don't exist for a second. There are multiple issues I have with the answer you linked. Besides, if you just look around the web, you'll see extremely varying answers and opinions about tides so its a really hard thing to get a straight, correct answer on. Kind of like the question about what makes planes fly.

@zephyr - I never wrote tides don't exist. I wrote that the tidal bulge doesn't exist. Laplace wrote pretty much the same thing when he came up with his dynamic theory of the tides.

Okay, tidal bulge instead of tides then. My claim still stands. I don't believe that it doesn't exist.

@zephyr - Humanity has been measuring the tides for centuries, including recently with extremely accurate orbiting radar altimeters. They don't see those bulges. They instead see Laplace's amphidromic systems. Newton's tidal bulges are a bit of a lie-to-children. While the concept explains the tidal forcing function nicely, it does not explain what happens on a rotating planet partially covered with a thin veneer of water. Laplace's theory does, and it doesn't have a bulge.

@DavidHammen Now I have to call you out. Are you talking about tides or tidal bulges! Tidal bulges 100% exist. That's just plain math and application of physics. I can agree that the tidal bulge may not always correspond to tides in the ocean for a variety of reasons like ocean currents, topology, etc. but the tidal bulge most certainly does exist. How could you explain the Moon moving away from the Earth, for example, if the tidal bulge did not exist? Furthermore, your linked question stating tides can't travel through water fast enough is faulty for the reasons one comment pointed out.

@zephyr - Yes, tidal bulges exist. The Moon has them. It has a mostly frozen set of bulge that wobble around a bit due to the eccentricity of the Moon's orbit. the solid Earth has them, but diminished because of elasticity in the solid Earth tides. These smallish tidal bulges and their time variations are hard to see, but they're their. The oceans on the other hand do not have the bulges you were taught about in high school or college. They cannot exist and they are not observed.

But they are observed, in the mid-ocean the tidal bulge is about 1 m. I observe it every time I go to the beach. The high/low tides occur exactly when I'd expect them to based on the Moon's location. Where I live, the oceanic tidal bulges are not affected by other forces.

What is observed is a set of amphidromic systems, each of involves tides rotating about an amphidromic point (where the tidal height is zero).

They are not observed. Maybe at a tiny handful of spots in the ocean you'll see high tide at the point explained by the position of the Moon. The vast majority, this is not the case. For example, the tides move north along the west coast of North America from Baja California all the way to Alaska.

At one of those points, the tides behave exactly the way Newton's bulge theory would explain. At other points, Newton's explanation is off by as much as six hours.

Those amphidromic systems explain the tides quite nicely all over the world. Newton's bulge theory does not. They are incompatible.

But you can break the tides down into various constituents. The largest by far is the diurnal tides from the Moon. As I said elsewhere, I can agree that there are other constituents that may affect this and cause it to not be the simplistic image you'd see in a basic textbook, but those diurnal tides are still there, even they're damped by other factors.

In fact, they very wiki page you linked me says "In most locations the "principal lunar semi-diurnal", known as M2, is the largest tidal constituent, with an amplitude of roughly half of the full tidal ran"

I think its misleading and wrong to say tides don't exist.

If you break the tides down by their constituents, you'll most definitely see the M2 tidal component -- but with a highly location-dependent phase angle. The concept of a bulge is at odds with this highly variable phase angle; it should be the same everywhere, and it should be rather small. Laplace's dynamic theory explains exactly why this phase angle varies so much.

@zephyr For crying out loud! I most definitely am not saying tides don't exist. They obviously do exist. It's the tidal bulge that doesn't exist.

Sorry, I keep interchanging tides and tidal bulge.

One of the biggest challenges after Newton was explaining why his concept of the tides was so very much at variance with what was observed. It took a couple of hundred years to get it right, but the picture was local. It took the last 60 or so years (the satellite era) to make that picture global.

I think this just all comes down to phrasing and interpretation.

It's not just phrasing. It's a matter of education. Earth scientists struggle with explaining why their would be two bulges. (The diagrams are ridiculous.) Astronomers and physicists at least get that part right. Getting the dynamics right is ridiculously hard for a rotating planet partially covered with a thin veneer of water is even harder. The concept of a bulge and the dynamically correct explanation are incompatible. That's not phrasing and interpretation.

I don

I don't struggle with explaining two bulges

That just comes right out of the math.

It's lying to children, but then forgetting that the next step in a lie-to-children is to move beyond the lie. Lies to children are necessary for making that next step in understanding. While the lie might be necessary for understanding, sticking with the lie is just wrong.

And what I meant was, I think that I agree with you, but not with how you describe your point.

@zephyr You don't need centrifugal force to explain the two bulges. All that's needed is gravitation. However, the Earth's oceans never have a chance to relax into that two bulge state. Gravitation describes the tidal forcing function. The dynamic theory of the tides describes the response to that forcing function.

Exactly, I wouldn't say centrifugal force plays a part in the bulges. In fact, I get frustrated when I see diagrams that say it does.

And honestly, I've never even seen a plausible explanation for how/why centrifugal forces could account for a bulge. Just bad diagrams and hand waving.

I think, all I was trying to get across is that the dynamic theory of tides does include that M2 term induced by the tidal forcing function. M2 does exist and is the largest component in tides. So as I said above, it seems misleading to me to say tidal bulges don't exist. They do, they're just tempered by other factors.

What Earth scientists call centrifugal force in their explanation of the tides is not what a physicist or astronomer would call centrifugal force. The Earth scientist's centrifugal force is the same at all points in or on the surface of the Earth. That makes no sense; centrifugal force has magnitude $r \omega^2$ where $r$ is the distance to the axis of rotation.

Nuts. No LaTeX here.

Well I completely agree with you on the centrifugal force issue.

Physicists and astronomers call that difference between the Earth as a whole (or any body as a whole) and a point on the surface toward some other body "tidal acceleration", or in extreme form, "spaghettization."

Aerospace engineers call the same thing "third body acceleration". They use the term "tidal acceleration" for the tiny acceleration that results from the influence of the tidal bulges in the solid Earth on a satellite in low to mid Earth orbit. (Ocean tides also perturb satellite orbits, too, but too a much smaller extent.)