[rmolnav]

In some places there is only one tide per day, where does the barycenter go?
Can one sea move on a barycenter, and another sea does not?

Regarding first question, apart from what said by Colin2B, I´ll only mention that the barycenter is some 2/3 of Earth´s radius off from its center, so "inside" our planet. But it is not something physical, just abstract stuff: the center of mass of total mass of Earth and Moon.
And it is the one which actually follows the elliptical orbit around the Sun, not the Earth´s C.G.
Regarding the second one, you have to keep in mind that we are discussing the root causes of tides, which are astronomical if you like. But due to the different continents and other varying local circumstances, ocean water is not free to move "obeying" only those root causes. In some places resonance and other phenomena may occur, and that can hinder or enhance tides in different fashions.   

[rmolnav]

What prevents a drop of water hanging on an apple, create two tidal hump?

Let us analyze that carefully ...
A "free" drop of water is roughly spherical. If hanging on (or "from"?) an apple, it actually has TWO kind of bulges.
The upper one, due to surface tension, would be equivalent to sublunar tidal bulge, in this case due to an "excess" of gravity attraction from the Moon, compared to centripetal force required for the circular movement of all water "drops".
And the lower one, due to the weight of all water of the drop, would be equivalent to opposite tidal bulge, in this case due to a deficit of gravity attraction from the Moon, also in comparison to required centripetal force. That defficit has to be compensated by the bulk of Earth´s mass, exerting an additional pull on water there, which, if not sufficient centripetal force, would inertially move outwards ... The equilibrium is reached thanks to 3rd Newton´s Motion Law: centrifugal forces turn up, as reaction to that additional pull from the bulk of the Earth.
That happens also where solid earth (and even in the atmosphere), and all across of the half of the Earth farthest from the Moon ...
Solid parts are stretched, and water, being much more free to move, deformes ocean surface shape until  own water weight "says": that´s enough ...
By the way, similarly to what happens at lower part of the drop hanging from the apple surface. In this case inward pull is water surface tension, and outward pull is water weight ...       

[rmolnav]

Clearly from the earth/moon rotational frame, they both rotate around a common barycentre,...

Just an important nuance.
The main purpose of my post of yesterday was to insist again that Earth doesn´t rotate around the barycenter: it actually revolves. Paths of points farther from the barycenter are not bigger than those of closer points. The circular path followed by every material Earth point has a radius equal to the distance from Earth´s own C.G. to the barycenter.

[Colin2B]

The main purpose of my post of yesterday was to insist again that Earth doesn´t rotate around the barycenter: it actually revolves.

Sorry, I was trying to reply to this post at the same time https://www.thenakedscientists.com/forum/index.php?topic=38127.msg540291#msg540291 and had a slip of the keyboard on terminology.
I agree with you

[PmbPhy]

pmb,
How does gravity push water away from the moon?

Due to the fact that he closer you are the stronger the pull of a gravitating body and the further you are away the less strong. This has the net effect of stretching whatever is in  the field.

And yes, for the most part there are only two tides per day, David is speaking about anomalies due to geometrical formations and that's not part of the two tides per day in oceans and seas. He never seems to mention those parts.

This link is from an authoritative source: https://oceanservice.noaa.gov/education/kits/tides/tides05_lunarday.html

[Colin2B]

This link is from an authoritative source: https://oceanservice.noaa.gov/education/kits/tides/tides05_lunarday.html

This one has more detail https://tidesandcurrents.noaa.gov/restles3.html

[rmolnav]

Sorry, I was trying to reply to this post at the same time https://www.thenakedscientists.com/forum/index.php?topic=38127.msg540291#msg540291 and had a slip of the keyboard on terminology.
I agree with you

Don´t worry: even without any keyboard slip, it´s easy to use the verb "to rotate" instead of "to revolve". But I wanted to insist on that detail, because the problem comes when somebody makes some dynamics analysis of it without keeping that in mind: the two cases are quite different.
Curiously, even the NOAA site linked by PmbPhy is not quite correct in that respect. They say: 
"The lunar day is 50 minutes longer than a solar day because the moon revolves around the Earth in the same direction that the Earth rotates around its axis".
They use both terms:
1) " ... the moon revolves around the Earth ..." But the Moon actually ROTATES, more exactly around the Moon/Earth barycenter, because it is tidal locked to our planet.
2) "... the Earth rotates around its axis". That´s correct, because the "revolving" of the Earth I previously referred to is  the some 28 day one around the barycenter. And they refer to its daily rotation. I prefer to say "spins" instead of "rotates" though ...

[Colin2B]

Don´t worry: even without any keyboard slip, it´s easy to use the verb "to rotate" instead of "to revolve". But I wanted to insist on that detail, because the problem comes when somebody makes some dynamics analysis of it without keeping that in mind: the two cases are quite different..

Yes, I’m aware of the technical difference, but I think the 2 get confused in common usage, spin would be clearer.
I generally prefer the barycentre explanation in the link I gave because it’s very clear where the forces and relative motions are occuring

I have removed the alternative theory posts to new theories as I think it is unfair go clutter up your thread.

[rmolnav]

Due to the fact that he closer you are the stronger the pull of a gravitating body and the further you are away the less strong. This has the net effect of stretching whatever is in  the field.

You and me have discussed this topic many times, and you always insist on the idea of differential gravitational forces, as if they were the only cause of the stretching, and eventually the tides.
But that "net effect", the result of a mathematical operation our minds can make, is insufficient: farther matter cannot "know" how big moon gravitational pull on closer matter is (in order to react to that "net" gravity), unless you consider internal stresses caused by the field of centripetal and centrifugal forces, originated by Earth´s revolving around the barycenter.
Colin2B has linked another work from NOAA. I learnt about it some months ago, but preferred not to bring it here because they go even beyond my stand, in relation to the use of the term
 "centrifugal force". I even contacted NOAA by mail, and one of them sent me a few mails.
I´ll further comment on that in another post replying to Colin2B post. But not today, because I´m afraid that, though they have gone in my line (considering centrifugal forces), they´ve gone "too far" ... And it will take long time to write something  sufficiently clear.

[rmolnav]

This one has more detail https://tidesandcurrents.noaa.gov/restles3.html

Colin2B has linked another work from NOAA. I learnt about it some months ago, but preferred not to bring it here because they go even beyond my stand, in relation to the use of the term
 "centrifugal force". I even contacted NOAA by mail, and one of them sent me a few mails.
I´ll further comment on that in another post replying to Colin2B post. But not today, because I´m afraid that, though they have gone in my line (considering centrifugal forces), they´ve gone "too far" ... And it will take long time to write something  sufficiently clear.

I´ll try to have it ready for tomorrow ...
Apart from that, I don´t quite understand what you mean when saying:

I have removed the alternative theory posts to new theories as I think it is unfair go clutter up your thread.

Perhaps I didn´t see some posts ...

[Colin2B]

Don’t worry about it, I like the method because it is clear on where the forces and relative positions of earth moon are. I can live with their terminology, I think it was written before the modern trend of explaining via inertia and frame dependant forces.

The other thread/posts I was refering to is https://www.thenakedscientists.com/forum/index.php?topic=73127.0

[rmolnav]

This one has more detail https://tidesandcurrents.noaa.gov/restles3.html

As I said two days ago, I saw that NOAA work last december. Previously I had seen another, also from NOAA, not completely in agreement with my stand. Then I contacted them, and one of its scientists and myself kept emailing each other for a couple of weeks. He was the one who sent me that link, and also another much more thorough:
https://tidesandcurrents.noaa.gov/publications/Tidal_Analysis_and_Predictions.pdf
though the analysis of root causes of tides are similarly long. The bulk of the much longer one is in relation with geographical local factors all across the world.
Then was when I posted #80 and 81. For me it was an "eureka" moment, especially for the "revolving" feature of Earth movement, in its necessary "dance" with the Moon to keep it in its orbit.
I saw that fact made compatible, as far as results are concerned, my "centrifugally influenced" stand, the one of so many who talk about only differential gravitational forces, and also the stand of those NOAA experts, which use the concept of centrifugal force beyond Newton´s Motion Laws.
I´m glad you "can live with their terminology", but others such as PmbPhy could say that to say total centrifugal force at Earth C.G. is equal to total Moon´s gravitational pull is wrong, because Earth is experiencing a centripetal acceleration ... They´d say that centrifugal force there wouldn´t be real ...and I agree with them. Perhaps they would bring up the issue of non-inertial systems of reference, what NOAA people don´t mention ...
And NOAA people also use "centrif. f." across the whole Earth, in a similar fashion, as one of the causes of tides ... But "fictitious" forces can´t produce real effects !!
I´m afraid all that is rather confusing. And that´s why I discussed with them. But no clear conclusion !!
I´m considering the possibility of copying here all those arguments of both parts, for anybody who could be interested.

[rmolnav]

I can live with their terminology, I think it was written before the modern trend of explaining via inertia and frame dependant forces.

I haven´t found the date of the NOAA "short" work, but the long one is actually dated 2007 ...
They mention centrifugal force as something kind of inherent to circular motion, without neither specifying which agent produces it, nor even mentioning terms such as centripetal acceleration and force ...
I´m afraid that is going to keep the big confusion existing out there, even among many physicists.
That problem is the one I first detected, and fight against, when I met this thread ... years ago. But to no avail so far !!
By the way, one of the first things I was told by the mentioned NOAA scientist was:
"The publication you are referring to is "Our Restless Tides", a 10-page pamphlet developed in the 1950's to provide a basic description of the forces which create the tides.  It's intended audience were the grade school children and adults of that time.  It used terminology of science and forces which were common in the 1950s.  Such as centrifugal force.  Centrifugal force was always an "imaginary force" (not a real / measurable force).  But that type of description made the concepts easier to understand and explain.  That  description and use of centrifugal force continued to be common practice until the 1970-80's.  At that point, the terminology shifted and the textbooks used in grade schools were changed to use a more modern terminology and description of this "effect" being a result of inertia rather than an "imaginary force".
RESULT OF INERTIA ... I do agree: Newton´s Motion Laws come from inertia !!
"THIS EFFECT" ... Centrifugal forces, in the cases when they are REAL, are not just an "effect" or tendency due to inertia ... Affected objects "tend" to keep their velocity vector due to their inertia, centrifugal FORCE is derived from inertia, but it is something more than that "effect" ...
   

[rmolnav]

I can live with their terminology

I´m quoting that again just to add that, as the core of our current discussion is the interpretation of the term "centrifugal force", and existing confusion, I´ve passed my previous post (#112) to the specific thread on the matter:
https://www.thenakedscientists.com/forum/index.php?topic=68025.new#new,
post #167 there.
It has induced several replies, some surprising because they show also a confusion among some of our "colleagues", the thread OP included ...
That made me send copies of the texts of a couple of emails sent by me to institutions with a very clear confusion on the issue. One of them the very Britannica dictionary.
I suggest anybody interested to have a look there.

[PmbPhy]

If the tides are caused by the gravity of the moon, why is there a high tide on the side of the Earth furthest from the moon as well as on the closest side?

Peter Conway

Asked by Peter Conway


                                        Visit the webpage for the podcast in which this question is answered.

[chapter podcast=1000585 track=14.01.07/Naked_Scientists_Show_14.01.07_1001836.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]

See: http://www.newenglandphysics.org/other/Taylor_tides.pdf

[rmolnav]

See: http://www.newenglandphysics.org/other/Taylor_tides.pdf

We have long discussed this issue ...
What said in linked site could not actually considered erroneous, but it´s insufficient. No clue is given to following question:
How "on Earth" could a portion of water far from Earth C.G. "know" the value of how much it would be pulled by the Moon if, instead of its actual position, it were situated where Earth´s C. G., and be able of deducting that vector from Moon´s pull in its actual position?
Because, as far as I can understand, material reacts only to the forces really exerted on it, either by CONTIGUOUS material (push, pull, hydraulic pressure ...) or "tele-forces" (such as gravity)
As early as #37 I refuted what you have said on #36 (rather than on #35, as erroneously said there).
No reply from you then ...
I´ve sent lots of posts, and though not many replies, I know there are people who agree with me (e.g. Colin2B).
Logically I can´t ask you to read now so many posts, but let me suggest you to have a look at #86 ...
Any further comment would be appreciated.

[rmolnav]

Don’t worry about it, I like the method because it is clear on where the forces and relative positions of earth moon are. I can live with their terminology ...

Hallow!
Just in case you haven´t recently read:
https://www.thenakedscientists.com/forum/index.php?topic=68025.new#new
I suggest you to have a look at, especially from #181 on.
I honestly think I´ve already grasp the ideas and method of my NOAA "friends", but I need some time to elaborate and send a clearly explaining post ...
PmbPhy intervened, and in my reply there is a kind of clue to what came to my mind in the eureka moment I mention:
"In particular, the centrifugal force is an inertial force which is observed in rotating (non-inertial) frames (a quote from PmbPhy post)
I´m afraid that is rather confusing ... What do you mean with "... which is observed in ..."?
Does it mean it is a real force "observed" by us? Or, in that "particular" case, is it rather a kind of tricky tool WE apply to bring a "fictitious" situation (an accelerating frame of reference) back to reality (with all REAL effects which have disappeared in that frame of reference)?

 

[PmbPhy]

We have long discussed this issue ...

And I explained it when I first mentioned it or was asked. The earth or moon doesn't "know" anything since they don't think.

Surrounding all planets there is a gravitational field whose strength decreases as 1/r[sup2[/sup]. IT's always there just like blades of grass are always on a gold course. A person or moon who which is in free fall in the earth's gravitational field will experience different forces on their body. If falling feel first then the feet will have a greater force on them than the force on his head. If will feel to the man falling that his body is being pulled apart. Same thing with the oceans on earth due to the moon's gravitational field.

If you're wondering why I didn't reply to something you posted its because I hold that you ignored what I posted. In particular the derivations for tidal forces and ocean tides and you refusing to prove that they are wrong, Homey don't play that.

[rmolnav]

A person or moon who which is in free fall in the earth's gravitational field will experience different forces on their body. If falling feel first then the feet will have a greater force on them than the force on his head. If will feel to the man falling that his body is being pulled apart

I thought it was clear that when I mentioned "think" it was just a rhetoric question ...
But a really "free fall" is only possible for material points ...
If a man is falling feet first, as you say his feet will have a greater force on them than the force on his head ... But both ends are not really in free fall, because they are kind of tight together through the body. Both have to get equal acceleration, and that implies that the body is somehow transmitting information between its parts ... The bulk of the body, accelerating according to gravitational field at body´s c.g., "forces" (pulls) upper parts not to let them fall behind, and pulls back lower parts, "forcing" them not to accelerate more than the c.g. ...
Those forces (certainly originated by the not uniform gravitational field), and their reactions (3rd Newton´s Law), are the direct cause of the "pulling apart" mentioned by you. It is not just a "feeling" due to the gravitational field gradient !!
That rather obvious idea has been present in all my posts, but, honestly, I´m afraid you feel too sure your rather "excluding" theory is the right one, and you´ve never taken "mine" worthy to consider. 

[PmbPhy]

But a really "free fall" is only possible for material points ...

That is incorrect. The term "free fall" is defined to mean "subject only to the force of gravity."

I have to stop here since I/m extremely busy with something else and you keep making false accusations about me, i.e. ad hominems. I don't tolerate that so I won't.