Tides

[matterdoc]

If cause of tides is gravitational attraction, solar tides should be greater than lunar tides. But it is not so.

Two independent forces on a body are likely to produce only one resultant action. Yet, gravitational attractions towards sun and moon produce two independent sets of tides.

[swansont]

If cause of tides is gravitational attraction, solar tides should be greater than lunar tides. But it is not so.

Two independent forces on a body are likely to produce only one resultant action. Yet, gravitational attractions towards sun and moon produce two independent sets of tides.

 

The cause of tides is differential gravitational attraction.

[D H]

If cause of tides is gravitational attraction, solar tides should be greater than lunar tides. But it is not so.

Two independent forces on a body are likely to produce only one resultant action. Yet, gravitational attractions towards sun and moon produce two independent sets of tides.

Utter nonsense.

 

See post #6 for the correct explanation.

 

(Topic was split. Post #6 is http://www.scienceforums.net/topic/52968-tides/page__p__574204#entry574204)

Edited December 7, 2010 by swansont
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[matterdoc]

DH,

 

Which is nonsense; Having smaller solar tides or having two sets of tides.

 

How many centers of gravity a single body may have?

[Sisyphus]

DH,

 

Which is nonsense; Having smaller solar tides or having two sets of tides.

 

How many centers of gravity a single body may have?

 

The Earth has 1 center of gravity, but that's irrelevant. Tides are caused by gravitational gradients. In other words, the difference between the force of gravity on the near side of the Earth and the far side.

 

The Sun's force of gravity on the Earth is obviously much greater than the Moon's. However, the force of gravity at high noon and at midnight (near side and far side) is very close. By contrast, the difference between the attraction of moon on the side of the Earth closest to the moon and the side farthest away is much greater, largely because the moon is so much closer. That's why lunar tides have more of an effect than solar tides.

[D H]

DH,

 

Which is nonsense; Having smaller solar tides or having two sets of tides.

Neither is nonsense. The tides can indeed be attributed to the Moon and to the Sun, and solar tides are smaller than lunar tides.

 

How many centers of gravity a single body may have?

And the point of this is?

 

 

 

[matterdoc]

Sysiphus and DH,

 

Quotes are from Encyclopedia Britannica.

 

“According to Newton's postulated law of gravitation, two bodies of mass m₁ and m₂, separated by a distance r. exert equal attractive forces on each other of magnitude proportional to m₁m₂/r². The constant of proportionality, G, in the gravitational law, F = Gm₁m₂/r², is thus to be regarded as a universal constant, applying to all bodies, whatever their constitution.”

 

During derivation of law of gravitation from earth-moon motions by Newton; “A further result, that the mass of the Earth acts gravitationally on the outside world as if the mass were concentrated at the planet's centre, was needed to obtain his relationship”.

 

Distance ‘r’ is between centers of gravity of the bodies.

 

“In physics, imaginary point in a body of matter where, for convenience in certain calculations, the total weight of the body may be thought to be concentrated” is called centre of gravity.

 

If we consider Newton’s law of gravitation, it seems pretty clear that a single body can have only one centre of gravity and while considering gravitational actions in conjunction with an outside body, all gravitational actions about the body have to be as if the whole mass of the body is concentrated at body’s centre of gravity.

 

Considering more than one centre of gravity (for different parts) of a body and correspondingly deriving for varying accelerations due to gravity of those parts is not intended by the above laws. Gravitational gradient may appear logical but I doubt if there is any provision for it in the laws considered.

 

* * * *

 

Earth is gravitationally attracted to both the sun and the moon. Thus, there are two independent external efforts, acting on earth, most of the time in different directions. By mechanics, earth should accelerate in a resultant direction. If earth’s (or its parts’) acceleration is the cause of tides, earth may have only one set of tides in the direction of its resultant acceleration.

 

During (syzygy) conjunction, earth’s gravitational attractions towards sun and moon are in the same direction. Attractions should add to each other to form a greater resultant attraction. Thus we have spring tide, which is combined sum of solar and lunar tides.

 

During (syzygy) opposition, gravitational attractions towards sun and moon are in opposite directions. Earth’s accelerations towards sun and moon tend to cancel (part of) each other. Resultant attraction and acceleration should be much less and in the direction of greater attraction. Yet we have spring tides, which is combined sum of solar and lunar tides, exactly as we have during conjunction.

 

Neap tides occur only when two independent sets of tides are at right angle to each other. According to your explanations, this happens, when directions of gravitational attractions and accelerations produced by them are perpendicular to each other. Isn’t there something strange about this?

 

This shows that tides, while keeping their independence, are able to add together or subtract from each other to produce resultant magnitude at any meridian. But, at least in cases of tides, forces or accelerations causing them are incapable to produce resultants, as dictated by simple laws of motion. This compels me to conclude that magnitudes of tides do not depend on the magnitudes of accelerations in any direction.

 

* * * *.

 

Relativity theories do not recognize attraction due to gravity for planetary orbital motion. Question of acceleration of earth towards sun or moon does not arise. Yet, earth has its tides.

 

* * * *

 

Often tides appear to lead or lag local meridian, even while direction of sun or moon are directly above local meridian. Although gravitational attraction is in local meridian, it appears that acceleration caused by it is deflected away from direction of force. This also is in contradiction with provisions of laws of motion. This further contradicts your conclusions that tides are caused by acceleration of earth or its parts towards sun or moon.

 

 

[D H]

Nonsense. You don't need relativity to explain the tides. All that relativity does in this case is to add unneeded complexity. Good old Newtonian mechanics does an excellent job of explaining the tides. George Darwin (Charles' son) and Arthur Doodson pretty much wrapped up the theory of the tides in a nice package, complete with ribbon and bow, and did so solely within the construct of Newtonian mechanics.

[swansont]

!

Moderator Note

Split from the main discussion on tides. matterdoc, hijacking threads to promote your own views will not be tolerated.

[Ophiolite]

If we consider Newton’s law of gravitation, it seems pretty clear that a single body can have only one centre of gravity and while considering gravitational actions in conjunction with an outside body, all gravitational actions about the body have to be as if the whole mass of the body is concentrated at body’s centre of gravity.

A consequence of this claim would be that there is no differential attraction upon different parts of one body by another body. In that case heating of Io's interior cannot be the result of tidal flexure of the satellite. Would you care to speculate what is responsible for the vulcanism on Io, the most geologically active body in the solar system?

[matterdoc]

Nonsense. You don't need relativity to explain the tides. All that relativity does in this case is to add unneeded complexity. Good old Newtonian mechanics does an excellent job of explaining the tides. George Darwin (Charles' son) and Arthur Doodson pretty much wrapped up the theory of the tides in a nice package, complete with ribbon and bow, and did so solely within the construct of Newtonian mechanics.

 

DH,

 

There is no point in saying 'nonsense', when you cannot answer. I raised only four doubts about cause of tides, which are obvious even to high school students. It seems you read only one of them, the doubt related to relativity theory. In this case, I quite agree with your answer. Answers to all other points are included in one collective 'nonsense'. All of them are related to Newtonian mechanics, which you consider infallible.

 

Even the moderator seems to think that the points raised by me are taboo and he transferred my posts to an obscure corner so that it may be viewed by as few people as possible. I can not see in which way I tried to hijack the thread away from discussion on tides or tried to promote my view, other than to express certain doubts about current explanations. It seems no thoughts against current teachings are tolerated in this forum.

 

You seem very confident and knowledgeable about the cause of tides being acceleration due to gravity. Your equations are beautiful and they positively state your view. Kindly clear at least one of my doubts.

 

Why are spring tides, both at opposition and at conjunction (when sun and moon are on opposite sides of earth) are equal? If you care, you can explain others also.

 

A consequence of this claim would be that there is no differential attraction upon different parts of one body by another body. In that case heating of Io's interior cannot be the result of tidal flexure of the satellite. Would you care to speculate what is responsible for the vulcanism on Io, the most geologically active body in the solar system?

 

Ophiolite,

 

It is not my claim. I only quoted an authoritative source.

Edited December 12, 2010 by matterdoc

[D H]

DH,

 

There is no point in saying 'nonsense', when you cannot answer.

I did give an answer, many times. I gave an inkling of the underlying math in this post, http://www.scienceforums.net/topic/52968-tides/page__p__574204#entry574204. I gave you names and keywords in post #8. I expected you to do some of your own research. I cannot give a full explanation of the tides in an internet forum. That would require me to write a book.

 

Your entire problem with understanding of tides is that you have a misunderstanding of Newton's law of gravitation. That misunderstanding is centered on this quote that you made from Encyclopedia Britannica. Quoting you from post #7, bold emphasis is mine,

"In physics, imaginary point in a body of matter where, for convenience in certain calculations, the total weight of the body may be thought to be concentrated"

So what are those "certain" calculations in which the mass of a body can be envisioned as being concentrated at the center of mass? The answer is that this simplification is only valid for rigid bodies with a radial mass distribution. The Earth's oceans make the Earth a non-rigid body. You cannot use that simple computation.

 

What you can do is make a series of refinements. You can start with a spherical, rigid Earth and put a single drop of water on the surface of that spherical, rigid Earth. Now you can apply that simple form of Newton's law of gravitation to determine the gravitational forces on that drop of water from the perspective of an Earth-fixed frame. The result is exactly what I showed in that earlier post. The picture gets a lot more complicated when you add lots of water and make the Earth itself non-spherical. However, it all starts with that simple calculation. This is the tidal forcing.

[matterdoc]

I did give an answer, many times.

 

No, Sir. You did not answer any of my doubts.

 

I will be satisfied if you will clear my one doubt as given in my last post: Why are spring tides, both at opposition (when sun and moon are on opposite sides of earth) and at conjunction (when sun and moon are on the same side of earth) are equal?

 

 

[Sisyphus]

No, Sir. You did not answer any of my doubts.

 

I will be satisfied if you will clear my one doubt as given in my last post: Why are spring tides, both at opposition (when sun and moon are on opposite sides of earth) and at conjunction (when sun and moon are on the same side of earth) are equal?

 

Tides are symmetrical - the bulge is on the near side as the attractor as well as the far side. (The near ocean is attracted more than the center, and the center is attracted more than the far ocean.) Two attractors on opposite sides will therefore add together the same as if they were on the same side.

[swansont]

Tides are symmetrical - the bulge is on the near side as the attractor as well as the far side. (The near ocean is attracted more than the center, and the center is attracted more than the far ocean.) Two attractors on opposite sides will therefore add together the same as if they were on the same side.

 

Which, it should be pointed out, is something D H addressed in the linked post, in showing that the acceleration is the same magnitude for the two cases.

 

Even the moderator seems to think that the points raised by me are taboo and he transferred my posts to an obscure corner so that it may be viewed by as few people as possible. I can not see in which way I tried to hijack the thread away from discussion on tides or tried to promote my view, other than to express certain doubts about current explanations. It seems no thoughts against current teachings are tolerated in this forum.

 

 

matterdoc, you should raise specific points, and need to do better than "You did not answer any of my doubts." What seems clear is that you either did not read or did not understand D H's post, since it quite clearly answers this point. As to the above sentiment, your posts have not been deleted, so claims that your views are taboo/not tolerated are demonstrably false. What isn't being tolerated is a violation of the rules. Your position that the current explanation of tides (a simple application of Newton's gravitation law) does not explain the phenomenon is diametrically opposed to any discussion of those effects. See rule 2.10. That's why this topic was moved.

[D H]

No, Sir. You did not answer any of my doubts.

 

I will be satisfied if you will clear my one doubt as given in my last post: Why are spring tides, both at opposition (when sun and moon are on opposite sides of earth) and at conjunction (when sun and moon are on the same side of earth) are equal?

 

Before I answer, I need to make a comment and then I need to ask you a couple of questions.First the comment. You have been making an argument from incredulity. That is a bad attitude to have when it comes to learning in general, and learning science in particular. There are many areas in science where people's intuition is just plain wrong. Now the questions:

1. Do you understand why your "two centers of mass" argument was incorrect?
   
2. Have you read up on tidal theory?

The latter question is rather important. I do not have the time, expertise, or inclination to write a complete dissertation on the tides. There are plenty of references on the web. Even better, go to a library and pick up a text on physical oceanography.

 

 

Now to answer your question: The answer is in http://www.scienceforums.net/topic/52968-tides/#entry574204. Note that the tidal force at the point on the surface of the Earth closest to the Moon and at the force at the point on the surface of the Earth furthest from the Moon are nearly equal in magnitude. (There is a difference, but it is very small.) Further note that that both forces are directed away from the center of the Earth. This makes for a nearly symmetric response. Because the response is symmetric, whether the Moon is new or full, the lunar and solar tides will add constructively. Just the opposite happens at first and last quarter. The tidal force is directed inward when the Moon is on the horizon. This means that at first and last quarter, the lunar and solar tides add destructively.