Talk:Gravity/Archive 4

message: The Nigel thread is now archived.  Hopefully this will be the end of the housekeeping for a while. --EMS | Talk 05:36, 23 July 2005 (UTC)
thread_title:  More archiving done 

message: The added section on scalar gravity was removed for the following reasons:
# I have not heard of this before.  So it probably is original research.
#* The link Introduction to Scalar Gravity is by Paul Bird, whom I suspect is the person behind this new section.  
# It is none the less a speculative theory.
#* The site treats the existing evidence for GR as being questionable, but offers no detailed alternative explanations for its successes.
#** Scalar gravity allows for no deflection of light by massive objects such as the Sun.  Other explanations are proposed, but no detailed analysis of them is done.
#** Scalar gravity allows for no non-Newtonian perihelion precession.  It is noted that there are potential Newtonian causes for the perihelion precession of Mercury.  The author is unaware that the perihelion precession of Mercury has been carefully analyzed, and the issue is an observed non-Newtonian component, as described in tests of general relativity.
# There is still too much GR stuff in this article for my liking.  As this is an alternative to GR, it would be much better being mentioned the general relativity article as one of the other theories.  This however assumes that it is even worth mentioning.  Also, if it is mentioned there, it must be with a one-line description.
So (as I see it) even if this anonymous poster (most likely Paul) can show that this is not his original research and is of some current or past acceptance in the field of gravitation research, it would at best rate an "honorable mention" on the GR page.  However, I will give him credit for a well-written web site, even if I cannot support this scalar gravity or its being mentioned here. --EMS | Talk 17:12, 11 July 2005 (UTC)
replies: text: Somebody just dropped into WP the article Scalar Gravity, you should watch this one, too. I'm also looking for published papers that can make this topic more than original research. Awolf002 21:08, 5 November 2005 (UTC)
thread_title:  Scalar gravity 

message: To answer D. Estenson II's question above:
gravitation is the tendency of massive objects to accelerate towards each other.
 
gravity is Newton's theory under which all masses exert an inverse-square law force on all other objects which is proportional to the mass of the gravitating object. 
So "gravity" specifically calls for there to be a force acting between objects while gravitation refers to the phenomenon in more general terms.  The reason for the distinction is beacuse in general relativity masses are not exerting a force on each other.  Instead, the way a gravitating mass bends spacetime causes other object (massive objects, photons, etc.) to accelerate towards it.
This is why an overview article can be written on "gravitation" with a fair part of what is in this article moved there.  What remains can then focus on Newton's theory instead of being part gravitation overview and part Newton's theory description.  BTW - This means that doing the proposed merge becomes obvious.
: This is where we disagree. Where are you getting your definitions from?  See, e.g. Merriam-Webster for more widely accepted definitions of gravity & gravitation. Gravity is a much more general term than Newton's specific theoretical formulation, and so those two articles should remain separate. I do now agree, however, that gravitation could be treated more generally than gravity. --D. Estenson II 03:29, July 29, 2005 (UTC)
:: Those definitions are incorrect.  It is obvious that the editor of that dictionary had no idea what they are.  In the popular press and for most people "gravity" and "gravitation" are synonymous, and that is what those definitions reflect.  I am not concerned with that.  Instead I an concerned with how scientists in the relevant fields understand those terms.  I think that I was told of the is distinction when I started taking general relativity courses.  The books tend to assume it in their titles.  See general relativity resources to see what I mean.  You can also see gravitation on brainydictionary.com.  --EMS | Talk 05:03, 29 July 2005 (UTC)
replies: text: EMS (and any other interested party), I am trying to write a little user manual on how to use some Portal templates. Unless you or others object, I would like to use the Gravitation portal (it doesn't exist yet) as my example. My idea is to take the lead sentences from selected sections of the Gravity article as content for this example portal. You are welcome to critique whatever you have time for (color selection, layout, images, etc.). This should address some of the issues you are bringing up with the current article, as a side effect. I am not trying to stir up trouble with the specific lead sentences and would appreciate whatever thoughts you have on the layout, etc. If you object strongly to this selection, I will simply choose another example set of content, to avoid conflicts. Ancheta Wis 04:41, 16 August 2005 (UTC)
thread_title:  Gravity vs. Gravitation 

message: First of all, for the caption that goes with picture of the astronaut in orbit:  Both the astronaut and the Earth are in freefall.  Anytime that you are weightles, you are in freefall.
Secondly, the Einstein Field Equations are solved to find the shape of spacetime in various situations.  They do not embody the Equivalence Principle, but intead assume it.  --EMS | Talk 03:02, 18 August 2005 (UTC)
thread_title:  Comments on portal 

message: I would like to see this done, and if the only person known to oppose this is Dennis then I will do it.  However, it would be nice to see if there is a consensus for or against this.  I kindly ask people to state their stand (support/oppose), with a brief explanation. --EMS | Talk 03:40, 31 July 2005 (UTC)
thread_title:  Poll on Law of universal gravitation merge 

message: This info might fit under History if you can give some reference to literature or an English translation:
:The Law of Gravity - 1200 Years Before Newton
:The Law of Gravity was known to the ancient Indian astronomer Bhaskaracharya. In his Surya Siddhanta, he notes:
:"Objects fall on earth due to a force of attraction by the earth. therefore, the earth, the planets, constellations, the moon and the sun are held in orbit due to this attraction".
:It was not until the late 17th century in 1687, 1200 years later, that Sir Isaac Newton rediscovered the Law of Gravity.
:Although Newton is one of the greatest mathematician and probably might has discovered without knowledge og the idea that existed already,unfortunately no one tries to remember Bhaskaracharya
For now I removed that text until we decide what to do. Awolf002 17:33, 27 October 2005 (UTC)
thread_title:  Bhaskaracharya 

message: If one could travel to the centre of a planet, what would the gravitational force be there?
:The Talk page is not the place to ask questions of this nature. It is used, ideally, to discuss the article. -- Ec5618 09:26, 28 October 2005 (UTC)
replies: text: Any questions that promote greater understanding of the article subject amongst editors are, I believe, suitable for inclusion on the talk page.--Light current 16:07, 28 October 2005 (UTC)

text: Zero, just like inside a hollow sphere, see Divergence_theorem#Gravity.--Patrick 11:00, 28 October 2005 (UTC)
replies: text: Thank you. I think you are correct--Light current 00:02, 6 November 2005 (UTC)
thread_title:  Gravity at planet centre 

message: The formula for calculating the gravitational force
 between any two objects has been given by Newton as:-
                   
                  F=GMm/R2
                   
Here G= universal gravitational constant,
          
M= mass of first object
m= mass of second object
          
R2= square of distance between the center of masses 
But in case of two concentric rings in the same plane ,which have virtual center of masses ,
R=0
Hence,
F= Infinite.
Thus , it will be impossible to separate them. Any circular disc can be said to be consisting of many such concentric rings. Hence it will be impossible to break such a disc. Similarly, it can also be said be for two concentric spheres , though even after the application of the shell-theorem, we will come to controversial results.Thus, Newton’s law is controversial.
To discuss with me, please mail me at XXX (rm email to evade spam-bots) 
--Vardhu7 17:57, 8 December 2005 (UTC)
replies: text: This argument is a little problematic.  The form of the law of gravity that you gave only rigorously (GR, QM aside) applies to two point masses and so cannot be used in the way that you did (beyond that it probably qualifies as OR) Threepounds 07:17, 12 December 2005 (UTC)
replies: text:  I think the error in this argument is "which have virtual center of masses," which seems to use the equivalency of the gravity field outside an extended spherical mass to a point source with the same mass. Since now the argument is about the inside field of an extended mass, this line of reasoning is incorrect. Awolf002 20:36, 17 December 2005 (UTC)
thread_title:  Vardhu7 comment moved here 

message: I'm having troubles parsing the second paragraph.  Can the author(s) clarify it?  Also the statement F = m\dot{v} + \dot{m}v isn't quite correct because of relativity (unless relativistic mass is used). Threepounds 07:25, 12 December 2005 (UTC)
replies: text: We could just revert to an earlier version. Right now, an external review would flag the 2nd para's content as an error. --Ancheta Wis 20:08, 17 December 2005 (UTC)
thread_title:  Second paragraph 

message: When I came to this article a few days ago I found it full of interesting information, but I felt the organisation could be improved. I have therefore reorganised and reordered the material fairly substantially, hopefully resulting in a better flow (though further improvements can still no doubt be made!) I have made every effort not to accidentally lose content in the process, or to garble what was already there. I have made a few additions and changes to the content of one or two sections where I felt competent to do so, but otherwise I have left the information content unchanged. Matt 21:53, 2 January 2006 (UTC)
replies: text: I second that!! Awolf002 22:56, 2 January 2006 (UTC)
thread_title:  Reorganisation 

message: :I wish we could derive the rest of the phenomena of nature by the same kind of reasoning from mechanical principles; for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards each other, and cohere in regular figures, or are repelled and recede from each other; which forces being unknown, philosophers have hitherto attempted the search of nature in vain.
This quotation is saying that Newton wished laws could be found like his laws of motion and gravitation that would explain all of nature. "I wish we could derive the rest of the phenomena of nature by the same kind of reasoning from mechanical principles." Obviously, he here wishes that all of nature could be explained by mechanical principles.  He was hoping for quantum mechanics, I guess.  He wants to explain why certain bodies repel and attract by mechanical principles. He wants to explain why attraction creates coherent figures i.e. it looks to me like he wants a law for why nature creates solid forms that cohere possibly hinting at atoms and the electromagnetic force. 
However, the information surrounding this quote is about causality and Newton's complaints about action at a distance.  This is the wrong quote for that and I will be removing this quote and putting in the correct Newton quote.--Voyajer 02:47, 8 January 2006 (UTC)
thread_title: I think this is not the appropriate quotation

message: :Similarly, when doing chin-ups, the electromagnetic interaction within the arms' muscle cells is able to overcome the force induced on the body by the entire Earth.
This is a mistaken understanding of bioelectromagnetism.  The truth is doing chin-ups is mechanically described by "work" done by the muscles using "leverage".
The electric nature of biological tissues permits the transmission of signals for information and for control and is therefore of vital importance for life. The first category includes such examples as vision, audition, and tactile sensation; in these cases a peripheral transducer (the eye, the ear, etc.) initiates afferent signals to the brain. Efferent signals originating in the brain can result in voluntary contraction of muscles to effect the movement of limbs, for example. And finally, homeostasis involves closed-loop regulation mediated, at least in part, by electric signals that affect vital physiologic functions such as heart rate, strength of cardiac contraction, humoral release, and so on. --Voyajer 03:51, 8 January 2006 (UTC)
thread_title: I have a problem with a statement and I am removing it

message: I think the article on Gravitation should be merged into the article on Gravity, for the following reasons:
*The vast majority of the Gravitation article is about the history of theories of gravity, which just overlaps and duplicates what is at Gravity.
*The only other information in the Gravitational article is:
**The definition: "Gravitation is the tendency of objects with mass to accelerate toward each other". Fair enough, but acceleration due to gravity is extensively covered in the Gravity article so why do we need a separate article to tell us this?
**The statement: "It is important to note that gravitation is not gravity. Gravitation describes a phenomenon independent of any particular cause. It is possible for gravitation to exist without a force, and according to general relativity, that is indeed the case." Maybe so, but GR is covered under Gravity, and any subtleties about the distinction between gravity and gravitation, with respect to GR or anything else, would more sensibly be included with that material rather than hived off into a separate article. (Incidentally, the Gravity article tells a different story, saying "Although the terms gravity and gravitation are used interchangeably, gravity usually refers only to the gravitational force between the earth and objects on or near it, whereas the term gravitation refers to the property of mutual attraction possessed by all bodies of matter.")
*The word "gravitation" appears throughout the "Gravity" article, most notably in the descriptions of "Newton's law of universal gravitation" and "Einstein's theory of gravitation". If "gravitation is not gravity" then what are explanations of these theories doing in the Gravity article?
Matt 21:02, 11 January 2006 (UTC)
replies: text: I am staunchly trying to keep these articles seperate.  As I see it, this article (gravity) should not mention GR except as an aside (in that it is what has superseeded gravity).  Indeed the discussion of theories other than that of Newton's theory of gravity should not be here at all.  However, part of what is needed to for someone to do the work of restricting this article to gravity proper and expanding the current "gravitation" article into coherent overview of the major theories (and classes of theories) of gravitation throughout history.  If I get the time soon, I will do the work.  For now, it is all that I can do to keep there from being backsliding in this regard. --EMS | Talk 22:35, 11 January 2006 (UTC)
replies: text:  In my view most readers will prefer (and indeed expect) to find the chronology of the various theories of the causes, explanations and properties of gravity summarised in one place, rather than split over separate articles. The distinction between gravity and gravitation - which I must admit I was not even aware of prior to coming across the Gravitation article - is something that should certainly be included if it has a sound basis, and sounds like it may deserve better (or at least consistent) coverage, but I think that it should be woven into a single narrative. Of course, if individual sections become too long then, sure, split out the detail to a separate article, but leave a summary at Gravity. Matt 01:14, 12 January 2006 (UTC)
replies: text: Agree. I agree with Matt, but EMS knows this already. I find the split into two articles to be strange and discomfiting. linas 02:35, 12 January 2006 (UTC)
replies: text:  Matt is on the right track here.  It's just that I think that the various theories of gravitation should be documented in the gravitation article, with the gravity article being restricted in scope to Newton's theory. This article also needs to be cleaned up in its use of the terms "gravitation" and "gravity".  They are not interchangable, although the difference is subtle.  I call on everyone to consider that insititutionalizing the endemic confusion between "gravity" and "gravitation" does nothing to belp either Wikipedia or its readers. --EMS | Talk 00:27, 28 January 2006 (UTC)
thread_title:  Merge Gravitation and Gravity articles 

message: Who is Fabrizio Bartolomucci and why is his wave theory of gravity listed under historical alternative theories? Googling "Fabrizio Bartolomucci" doesn't turn up anything relevent or scholarly related to gravity, or perhaps the name was mispelled?
:Agreed, this section is not referenced and unverifiable. I will remove it. Also, the user adding it was Fbartolom and so this might also violate WP:VAIN. Awolf002 19:45, 6 February 2006 (UTC)
thread_title:  Fabrizio Bartolomucci? 

message: Bold text Gravity is a force of oxygen not an attraction of a force!! But if what Fabizio or w/e sad about Gravity is true than man, my Science teacher needs to get a new job or go back to school!...even my dad who was a Science Scholar agrres with me!!!
Please add more if you please!!!
- 72.132.56.178 01:00, 14 February 2006 (UTC)
thread_title:  New definition of gravity!!  

message: Isn't it true that gravity and accelerated motion are indistinguishable? For example, absent all other forces, a rocket accelerating (and pushing against the astronauts' feet) at 9.8 m/s2 would have exactly the same gravitational effect on the astronauts, as the rocket being stationary on earth - with the earth pushing against it (and everything else) at 9.8 m/s2 (same as saying that the everything is accelerating towards the earth's centre at 9.8 m/s2). In both cases the astronauts would weigh the same. I did not see this mentioned in the article...? Rohitbd 14:12, 16 February 2006 (UTC)
replies: text: Hello. Please sign your posts with ~~~~. I do agree that we have so far succeeded only in explaining what gravity does or how it behaves, but not "what it is". Every object in space attracts every other. So jupiter attracts the sun just as the sun attracts all other planets. Even human beings attract the earth - just that the mass of humans is so small compared to earth's that when a human falls towards the earth s/he gains much more momentum than the earth. As to why things are in orbit, it is because each planet is moving at just the velocity needed to keep it in orbit. Just as a satellite launched from the earth has to be moving at just (over?) the earth's escape velocity to get into an orbit and once in orbit it maintains that orbit if it maintains its speed. Rohitbd 10:01, 23 February 2006 (UTC)
replies: text:  Under the equivalence principle, what Rohitbd writes is true.  However, that is part of the foundation of general relativity in which gravitation is due to spacetime curvature instead of a real force exerted by one massive object on another.  There is a difference since in Newton's theory freefall is an accelerated state of motion, while in general relativity it is inertial motion.  In any case, this article is about gravity instead of general relativity, which is why is not only is not mentioned by should not be mentioned. --EMS | Talk 21:03, 24 February 2006 (UTC)

text: Well, I'm not an expert but from what I know, gravity is an intrinsic property of matter. Where there is matter, there is gravity. And gravity is always felt as an attractive force. Rohitbd 12:35, 26 February 2006 (UTC)
thread_title:  Gravity and accelerated motion