The tide doesn't actually come in and out

[-FX-]

Originally Posted by LarsMac

And, the "Twin Bulges" notion is not really a "Thing" other than as a logic tool created by scientists trying to develop analogies to help explain the phenomenon to the simple laymen.

I wish that was the case. It is not.

The big mistake is telling people there is a bulge on the opposite side of the world from the moon, and that the moon causes that bulge. This is to explain the second tide, in places that have two high tides a day. It's wrong. In fact, there isn't any bulge at all. On either side, or under the moon.

Originally Posted by LarsMac

So, question:
IF you wanted to explain the grander concept of the tides to your four-year-old nephew, would you present them with "LaPlace", or with the "Twin Bulges"?

I would use both, making it a brief history story. Starting the Newton, bringing in LaPlace, and ending with watching videos of the satellite data and models

[LarsMac]

Originally Posted by -FX-

I wish that was the case. It is not.

The big mistake is telling people there is a bulge on the opposite side of the world from the moon, and that the moon causes that bulge. This is to explain the second tide, in places that have two high tides a day. It's wrong. In fact, there isn't any bulge at all. On either side, or under the moon.

I would use both, making it a brief history story. Starting the Newton, bringing in LaPlace, and ending with watching videos of the satellite data and models

That's a bit deep for a 4 yo, IMHO. I suggest starting with a trip to the beach.

So, if you object to the term, "Bulge" what better term might be acceptable?
I think that "Bulge" strikes me as an attempt by popular scientific personalities to oversimplify the explanation. But, what better word might fit the description of a significant mass of water moving around the globe?

There is a tidal rise that follows the Moon, and a secondary Tidal rise often approximately opposite of the Moon.
It seems rather obvious that the gravitational interactions between Earth and the Moon are in some way responsible for all that sloshing about. Do you disagree?

[-FX-]

Originally Posted by LarsMac

So, if you object to the term, "Bulge" what better term might be acceptable?
I think that "Bulge" strikes me as an attempt by popular scientific personalities to oversimplify the explanation.

I don't object to the term. It's that there isn't a bulge, much less two of them, following the moon around the earth. Using a description of something that does not exist, to explain something we all know exists, is absurd. And unscientific.

Originally Posted by LarsMac

But, what better word might fit the description of a significant mass of water moving around the globe?

First, no "significant mass of water" moves around the globe. From the tidal force of the sun and moon. The movement that does occur is called the Tidal Current

Tidal currents can be defined as the periodic movement of water driven principally, though not necessarily exclusively, by a head difference created by out-of-phase ocean tides at each end of a restriction

And those currents often do come in and go out, especially in harbors or bays.. Of course the ocean tides certainly seem to come in and out, and of course the moon is the main driver of such movements. It's just that what is actually happening is due to very large Amphidromic systems.

Amphidromic Systems get the name from the Latin words amphi (around) and dromic (running). In essence, they are bodies of energy shaped by the gravitational pull from the moon and set in motion by the spinning of earth on its axis.

Originally Posted by LarsMac

There is a tidal rise that follows the Moon, and a secondary Tidal rise often approximately opposite of the Moon.

No, that's where the "bulges following the moon" fiction really breaks down, for several reasons. (The big one being the bulges do. not exist lol)

Once you look at the Amphidromes you can literally see what actually is happening.

I made that animation back in August 2010, when this argument started online.

Originally Posted by LarsMac

It seems rather obvious that the gravitational interactions between Earth and the Moon are in some way responsible for all that sloshing about. Do you disagree?

Of course not. The moon and sun are exactly why the ocens have tides, and tidal currents.

[-FX-]

Here's an animation of the tidal forces, showing how the "sloshing around" starts, and what the actual ocean tides look like.

Animation of the tides around the globe - YouTube

If you observe carefully you can see the 12 major amphidromic points, the ones shown in the gif animation above.

[LarsMac]

OK, I know all that, but I wasn't planning on digging down to the nuts and bolts.
you win.

Though even in the less huge bodies of water there is quite a bit of "Sloshing around" done by the gravitational forces of Sun and Moon interacting with our own gravity.

All of the "sloshing around" in those images is pretty much the result of the Tidal "Bulge" interacting with the continents.

[fragment]

I'm with F X here. There are no bulges. There are periodic forces (simplified but that's what we're doing here). I reckon kids can get an intuition about periodic forces (and resonance) - put them on a swing. If you're OK with mopping put them in a bath and get them to slosh the water around to see how water moves as a body in response to periodic force. Or you could try sloshing and stirring in various containers to see how shape and size affects the response.

Better to develop an intuition of these kinds of basics than to teach an oversimplified-to-the-point-of-being-wrong model that will have to be unlearned later.

Of course, I have little experience in either child raising or science communication, so grains of salt, etc.

[LarsMac]

Whatever you want to call it, the "Bulge" actually isn't in the water.
That's the point that has been overlooked, I think.

And the water is sloshing around, because it is in a collection of "Basins" that is moving, with a number of forces at play, including the gravitational forces and interactions of the various spheres, and the walls of the various connected "basins" in which the water resides.

[fragment]

I'm not sure "there are bulges in the ellipsoid formed by the hypothetical equipotential surface if the system stopped various orbits and rotations (whilst maintaining relative position) and came to equilibrium"* is more useful as an explanation than saying something about periodic changes in gravitational force experienced at points on the surface due to the changing direction from those points to the moon (and sun to a lesser extent) as the planet rotates (and the earth and moon orbit). And presumably coriolis effect.

* or whatever, too lazy to check this formulation for accuracy

[LarsMac]

Originally Posted by fragment

I'm not sure "there are bulges in the ellipsoid formed by the hypothetical equipotential surface if the system stopped various orbits and rotations (whilst maintaining relative position) and came to equilibrium"* is more useful as an explanation than saying something about periodic changes in gravitational force experienced at points on the surface due to the changing direction from those points to the moon (and sun to a lesser extent) as the planet rotates (and the earth and moon orbit). And presumably coriolis effect.

* or whatever, too lazy to check this formulation for accuracy

Well, yeah, to the average Joe on the streets, not much that stuff matters a whole lot. But for a guy who works as a janitor at the Planetarium, it can be something to tell the grandkids about. And if you happen to be one of those grandkids, then it could be something to tell your fellow scouts around the campfire.
Ya never know.

[-FX-]

Originally Posted by fragment

Or you could try sloshing and stirring in various containers to see how shape and size affects the response.

Yes. If you scroll down slightly to the graphic on the linked page (the image can't be hotlinked)
Amphidrome.

there is an illustration of how the tides actual are. Using a bucket you can show a child a simple amphidrome by simply moving the bucket to create one.

This is actually how Semidiurnal tides actually work. The two high tides each day are from the same amphidromic system. Each high tide is the same giant stationary wave crest returning. And it doesn't "come in" so much as it rotates in. (again, bays and harbors are different)

Originally Posted by fragment

Better to develop an intuition of these kinds of basics than to teach an oversimplified-to-the-point-of-being-wrong model that will have to be unlearned later.

I agree. Especially the part about the bulge on the far side, away from the moon. Since that doesn't exist, the explanation for it is nonsense. (there are actually three different explanations, and all are nonsense)

Originally Posted by fragment

Of course, I have little experience in either child raising or science communication, so grains of salt, etc.

I felt a bit of sadness when I read that. Teaching children (even if you are not raising them personally) is one of the most amazing things one can do in our lifetimes. It's certainly not for everyone.

I think part of the joy, is that when teaching, or showing a child something new, they are seeing it for the first time. It's a wonder to them. And if we are fortunate, we get to remember that same wonder we experienced, when we were a child. Where everything is new, and amazing.

It can trigger long forgotten memories and feelings.


But that is going way off topic, isn't it?

[-FX-]

I find the true nature of the ocean tide to be far more interesting than the fictional "giant bulge" or "hump" of water that is said to "follow" the moon. These massive circular waves, all rotating and interacting, even sweeping around the entire North Atlantic basin each day, that is a fantastic thing to learn.

The "twin bulge" idea never made sense. If such a thing did exist, we would have to explain what happens to all that wave energy when it smashes into the solid wall of the continents. And how could a wave that long move fast enough? (the oceans are far too shallow)

The only system that could work is the one we observe, where energy is conserved. And it still has enough friction involved to slow the earth's rotation over time.

[LarsMac]

Originally Posted by -FX-

I find the true nature of the ocean tide to be far more interesting than the fictional "giant bulge" or "hump" of water that is said to "follow" the moon. These massive circular waves, all rotating and interacting, even sweeping around the entire North Atlantic basin each day, that is a fantastic thing to learn.

The "twin bulge" idea never made sense. If such a thing did exist, we would have to explain what happens to all that wave energy when it smashes into the solid wall of the continents. And how could a wave that long move fast enough? (the oceans are far too shallow)

The only system that could work is the one we observe, where energy is conserved. And it still has enough friction involved to slow the earth's rotation over time.

Yeah, a lot of scientific stuff doesn't "make sense" to the average bloke.

But the water doesn't "Smash into the continents" it generally just flows around things that are in the way. That's one of the cool things about water.

[-FX-]

If there actually was a huge bulge of water following the moon, with the crest moving at 1000 mph at the equator, and it encountered the continents, like North and South America, where there is no "going around", you would have to explain what happens.

But of course there are no bulges, even in the Pacific ocean, where the ocean is almost half the circumference of the planet, and has no continents to disrupt a bulge. Which does not exist.

No matter how many official videos and lessons tells us there is.

[LarsMac]

Originally Posted by -FX-

If there actually was a huge bulge of water following the moon, with the crest moving at 1000 mph at the equator, and it encountered the continents, like North and South America, where there is no "going around", you would have to explain what happens.

But of course there are no bulges, even in the Pacific ocean, where the ocean is almost half the circumference of the planet, and has no continents to disrupt a bulge. Which does not exist.

No matter how many official videos and lessons tells us there is.

Now, THAT's funny.
Did you actually write that?
Or did your twelve-year-old kid sneak onto you computer tryin' to make you look stupid?

[-FX-]

Never take yourself too seriously. Nobody else does

[LarsMac]

Originally Posted by -FX-

Never take yourself too seriously. Nobody else does

Yup. We all get what we'll settle for.

[-FX-]

The tides are caused by the rotation of the Earth in the presence of the gravitational pull of moon and sun.

The often repeated idea that there is a water 'bulge' traveling around the globe, being balanced by an equal bulge on the other side, so that a shore "rotates into the tide bulge", was debunked in 1776.

And yet, to this day, the majority of people on the planet believe in the bulge, and every young person is taught this completely false idea.



Here is the video at that point the screen grab is from

Neil deGrasse Tyson Explains the Tides - YouTube

36 seconds in if that doesn't work

Neil deGrasse Tyson could have explained the far more interesting truth, explaining the amphidromes and how the sun/moon system pumps energy into the resonating circular waves, but he doesn't. He probably doesn't even know.

Most people don't. I know you didn't before reading this topic.

I used the following phrase about 14 years ago, in an argument about the matter.

"The Kelvin wave propagates along the coast at the shallow water speed." The small mob of morons, all arrayed against the very idea, mocked and jibbered like monkeys flinging poo

Seriously. It's from a texbook, that I happened to own. (I own several others as well)

Coastal Dynamics (Bosboom and Stive)

Much like the stinging stupidity of "did your twelve-year-old kid sneak onto you computer tryin' to make you look stupid?", the completely ignorant fuckheads thought I had written something stupid. (it went downhill from there)

I had previously explained pretty much everything I was writing was from either Satellite data, (TOPEX and JASON), papers on the sat data, college textbooks, or from University lectures and class material. Or even old papers from LaPlace and Newton. Of course it didn't matter to the league of morons.

Every last one of them. to a person, still thinks there are twin bulges, and the very idea of Amphiromic systems (Kelvin waves) is some nonsense I made up. Which is truly fucking hilarious.

3.8.3: Kelvin waves - Geosciences LibreTexts

But it get's even better. Oh so much better.

And yes, I know you probably are not going to believe it, but it's true.

[LarsMac]

Well, I'm glad you're having fun with this.

A lot depends entirely upon your perspective, of course.

As I said before, living near the coastal regions much of my life, I can assure you that in many places in the world, the tide does, indeed, "Come in" and "go out" with a predictable regularity. And there are regions of the world, also related to large bodies of water, where there is little, if any tidal variations to be perceived. That actually has some relevance to you Amphidromic behavior.


Oh, and there actually is a "Bulge", but, it's not really in the water.

[-FX-]

Originally Posted by LarsMac

Oh, and there actually is a "Bulge", but, it's not really in the water.

The solid earth tide could be considered a bulge. If you really stretched the definition of "bulge".

The variation is around a foot, from low to high, which is over a 12,000 mile distance. That would be at new moon, when the tidal forces are at maximum. And it's real of course. The LHC has to adjust the proton beams orbits.

For the 27 km LHC circumference the difference can be like .35 mm (rough estimate)

Depends on where the moon is in relation to the LHC

I have a graphic somewhere showing the earth tides .... hang on a sec ... OK here it is

Originally Posted by LarsMac

Well, I'm glad you're having fun with this.

I'm always having fun. If something isn't fun on the internets, why would anyone keep dping it? I mean, unless you are getting paid, why would anyone do something that wasn't fun? Especially for like, years and years.

Now to wrap up the insanity I discovered.

[-FX-]

I just can't. Every time I start, it just seems like it will either sound too insane, or I realize it's a complete waste of time.

This is also the problem with almost every other topic.

[LarsMac]

So, like, A whole new meaning to "Solid Earth", Hmmm?

[seebs]

Originally Posted by LarsMac

Oh, and there actually is a "Bulge", but, it's not really in the water.

Goddammit can I never be free of Homestuck.

[-FX-]

The earth tide is very small.



If the ocean tides were like the solid earth tides, most places wouldn't notice them. And even where they were at maximum, there would be a very small rise and fall, with small tidal currents.

[LarsMac]

Originally Posted by -FX-

The earth tide is very small.



If the ocean tides were like the solid earth tides, most places wouldn't notice them. And even where they were at maximum, there would be a very small rise and fall, with small tidal currents.

And if a frog had wings,..., yeah, yeah.

Sorry that yer so disappointed in Kansas, Chum.
Of course, those few millimeters can make a difference in places where mountains of rocks can get a bit disturbed by everything moving about, even just a little bit.

[seebs]

that's an almost 50cm difference in height, which is honestly sort of enormous compared to what i would have thought the earth does. 50cm is a *lot*.

Having been to a beach ever in my life: 50cm would be enough to get noticed quite easily. And a little over +0.3m to just above -0.2m is in fact about 50cm.

So for those who are not used to metric: That's like having a thing where at one point in the morning two surfaces are completely flat with respect to each other, and then in the evening it's too high to step down and you have to jump or climb.