Talk:Weight/Archive 2

Archive 1

Archive 2

Archive 3

Article is worse than ever

Parts of the article seem to have been hacked around by someone with only a loose grasp of English. It needs a complete rework. I think it's worse now than ever. —Preceding unsigned comment added by 86.185.76.35 (talk) 03:42, 10 May 2010 (UTC)

• I put it back to what seems to be the last clean version. I agree that this article (and Apparent weight) are in need of expert attention, but ramming in a whole load of poor quality edits isn't helping the cause. —Preceding unsigned comment added by 81.159.76.178 (talk) 19:12, 10 May 2010 (UTC)

Again, Mass NOT the Same as Weight !!!!!!!!!!!

I was rewriting the article to a better point, I found it, after some weeks, to have been basically reverted to the point that some funny dudes think mass and weight are the same thing because the absolute value of weight (scalar, the number)is proportional to the mass.... NOT THE SAME, period. There's no everyday application in which you can say your weight is your mass and you are speaking correctly !!!!.

Proportionality of a vector's absolute value and a scalar cannot lead to think that the vector and the scalar are the same (does it make any sense?). i.e: Friction in a fluid is proportional to a constant, that is a characteristic of the fluid, yet the constant cannot be mistaken for the friction (force) or the velocity (the speed a particle is carrying out whilst breaking into the fluid), Nor momentum can be mistaken with velocity even though they are proportional (the mass).... So NO!!! you're wrong Mass and Weight are not the same!!! this topic should be edited strictly by physicists or engineers and no other sort of people, IT'S a SHAME to the Wikipedia Model of cooperation to have such a long arguments about this very easy topic, it speaks negatively of the people who edit articles here... I will see if after sorting out some other stuff I put some time into it....

and as for static equilibrium, imagine you let a rock to fall at a distance (some hundred meters for instance) of the moon surface, there's no atmosphere then no friction, the rock is moving towards the center of the moon then no static equilibrium, then is there a weight? ... of course there is!!! that's why the object is moving, and it equals to the gravitational force that is acting on the little rock... so no, you cannot argue static equilibrium as a condition for there to be a weight and for it being the gravitational force that acts on the particle/body.

As for the history, Why don't we edit the Earth article and say it is flat? humanity used to think of it that way, no? so articles are written the way we know they are now. Plus it was only with Newton that the concepts of Mass and Force began to be truly understood.—Preceding unsigned comment added by 190.71.18.167 (talk • contribs)

The part that you deleted dit not say that mass is the same as weight. It says that sometimes, in everyday language, the terms are interchanged. This is sourced. Please stop removing this.

Also, please sign your talk page messages, and please open new sections at the end of the talk page. Thank you. DVdm (talk) 22:01, 15 May 2010 (UTC)

Agree with DVdm (is your name the reciprocal of density?). The IP is correct that mass and weight are different, but the article does not even say they are the same (it even says that they are different, strictly speaking). It does say that laymen sometimes treat them like they're the same, which is a common practice/misconception whose explanation is relevant should be kept in this article. 71.113.18.192 (talk) 22:49, 15 May 2010 (UTC)

The article currently reads: "In practical or everyday applications, weight means the same as mass as that term is used in physics"

If you say in a practical, every day application that weight is the same as mass then you are making a mistake, it is that simple, sorry.

Reason for having removed my un-sourced non-sense (in which it had been stated there's the common misconception of taken weight for mass and viceversa) was because of lack of references, then, unreferenced article is one thing(sorry, I just didn't reference the books I've studied (I have only 1 with me, now, i'd need to look in Internet for other codes), I thought to do it at the end, as I simply edited a couple of paragraphs), misconception is another.

Plus remember one thing, having one misinterpreted source doesn't allow one self to claim veracity on an statement published in an article in Wikipedia (which has become common practice: To barely understand something and then add sources that don't re-affirm one's words)

I may be making some mistakes (redaction mistakes that can lead to the concept to be not clear or mistaken) we can talk them through, but people have to know already the thing and not falling into the other proplem of wikipedia: To buy other people's opinion based on poorly understood sources or eloquence... —Preceding unsigned comment added by 190.28.95.156 (talk) 02:46, 16 May 2010 (UTC)

It's OK to mention mass, but the article must be primarily and mostly about about weight, not mass. The article on mass is at mass. Wikipedia is not a dictionary, so the article is not about the word weight, and the usage of the word weight. Please keep that in mind.- Wolfkeeper 03:49, 16 May 2010 (UTC)

Molecular Weight, Molecular Mass

mhmhmh... well, I didn't study too much chemistry, I did study crystals when in the University, as well as thermodynamics as part of the basic physics courses, and a little bit of quantum mechanics, so checking on the periodic table I had to use during those days, it does read Molecular Mass. I might be wrong but Molecular weight can be just another way how not-so-into-the-topic people get confused with terminology. It should be good to have one written example an officially published book, or table that actually reads "Molecular weight" ... sure there's gravitational force exerted by the Nucleus on the electrons (if you take Bohr's model of electrons in orbits as opposition to quantum mechanics) but I don't think that's what the periodic table refers to... —Preceding unsigned comment added by 190.28.213.152 (talk) 03:52, 16 May 2010 (UTC)

Units section

There are several problems, I was going to go for a paste text here and comment what is wrong, but you'd agree that it is too faulty. Also, the fact that you have a reference, doesn't make it valid straight away, references don't buy validity in all cases.

For instance the sentence: "Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb 'to weigh' means 'to determine the mass of' or '"to have a mass of." found in a reference is wrong (it also has typos), since, as we have discussed (and every one who has studied this very basic stuff knows), kilogram is a unit for mass and weight and mass are different.

pound is not a unit of mass and a unit of force, there's pound (mass) and pound-force what's more you have the expression: pound-force = 32.17405 pound_mass·ft/s².

removing tables with wrong formulas like force=m*acceleration/acceleration=m (very wrong) tagged for revision since 2009.

the section is left with plain information, no debates or points to be made. Expand only if you already understand. —Preceding unsigned comment added by 190.28.208.187 (talk) 05:01, 16 May 2010 (UTC)

"Coverting between force and mass" section

As the title of the section suggests, it is incorrect and the inclusion of such section has been tagged for evaluation for permanence in the article.

Then since the scope of the article is not to teach how to do simple algebraic manipulation, the title of the section is misleading, the other information provided is already contained in the other sections then I'm removing it. you can undo, but give it a little discussion here first; bear in mind that we already know converting between numbers and vectors is not possible, nor converting between cats and dogs. —Preceding unsigned comment added by 190.28.208.187 (talk) 05:25, 16 May 2010 (UTC)

Useful overview

The paper "The Semantics Problems on the Definitions of Weight" by Wong Chee Leong and Yap Kueh Chin from the National Institute of Education (Singapore) provides a useful overview of the various definitions of weight and the attendant issues. I don't know if this by itself counts as a reliable source – as far as I can tell the paper has not been officially published –, but it has references to reliable sources that support the material presented.  --Lambiam 13:50, 31 May 2010 (UTC)
The paper was apparently presented at the ERAS Conference 2009: Unpacking Teaching and Learning through Educational Research (see the Conference Programme at Paper No. 2-4-34). It does not appear that the full papers were peer-reviewed.  --Lambiam 14:57, 31 May 2010 (UTC)

Somewhat interesting read. It nicely summarizes some of the issues we had already encountered in this article. Not sure about its suitability as an RS, though. But it does give a nice overview of other sources (many of which are already cited in this article). TimothyRias (talk) 15:07, 31 May 2010 (UTC)

While it is true that papers presented at conferences have not been refereed, if they are presenting information that is already well-known, they are usually reasonably reliable. In such circumstances I would normally be happy to reference them, if only because other readers can also access them. Martinvl (talk) 16:00, 31 May 2010 (UTC)

Non-uniform gravitational fields, graviational gradients

Shouldn't this article also cover weight in non-uniform gravitation? 76.66.193.224 (talk) 07:07, 3 June 2010 (UTC)

It says: "The gravitational acceleration varies from place to place," so in a sense it already does cover non-uniform gravitation. It's not much, but it's something :-) - DVdm (talk) 14:14, 3 June 2010 (UTC)

Sensation of Weight

I am surpried that the section on Sensation of Weight makes no reference whatsoever to the ear. My understanding (from school bioogy lessons) is that the ear contains the organ of balance and that it is here that the sensation of weight is measured. Martinvl (talk) 07:08, 31 May 2010 (UTC)

It should be mentioned, although it's more the sense of up-and-down you get from the inner ear. Underwater, at neutral bouyancy and no visual cues (for example, doing scuba in an underwater cave) many people have found out that a lot of the sense of up-and-down is (was!) generated by pressures on the body and by the eyes. Some divers have had to resort to looking at the direction their bubbles rise to tell which way is "up." Other divers, however, are fine and never get disoriented that way. Some people are like cats, and their inner ears are just better than others. So this varies. The sensation, by the way, is caused by otoliths in the utricle (ear) and saccule in the inner ear. These little rocks fall down against hair cells and this tells a person the absolute orientation of the head (if it's all working correctly). SBHarris 08:07, 31 May 2010 (UTC)

I agree that the current version, ascribing the sensation solely to the vestibular system, is dubious; see Spatial disorientation for how easily one can loose a correct sense of up and down in the absence of reliable visual cues. While important for the sense of balance, this exteroceptive sense is not the only and perhaps not even the most important one for the sensation of weight. Interoception and proprioception/kinesthesia are also involved. The latter tells one how hard it is, for example, to lift one's arm and hold it up in a given direction. The human body is flexible and deformable, particularly the softer tissues, and weight makes one's body sag, causing stresses and strains. Various internal stretch receptors will signal that; also, muscles will be contracted to counteract the sagging, and again stretch receptors will report the increased tension in muscles and tendons. My guess is that actually the last bit is what contributes most to the subjective sensation of weight of someone subjected to high g-forces, but we need reliable sources before any of this can be added.  --Lambiam 14:42, 9 June 2010 (UTC)

To be fair we should note that SOME (not all) of the problems discussed in Spatial disorientation are problems that would fool an accelerometer, too, since they result from "fictious forces" (intertial forces) arising in the accelerated frame of an aircraft, which counteract or modify the direction of gravity. The inner ear in many people is very good at telling you what the g-force is-- but (alas) it doesn't always point toward the ground! These things don't "fool" a gyro, because acceleration and spacial orientation are two different things and a gyro will tell you when you're in a perfectly coordinated banking turn when the "seat of your pants" (and your inner ear) will not. The situation of neutral boyancy in dark water, where all visual cues are removed and most (not all) of the body stress cues, is a better one for trying to figure out the contribution of the inner ear mechanisms. SBHarris 19:03, 9 June 2010 (UTC)

190 at it again

Anonymous IP 190 was at it again. Not content with the statement in the article that "In modern scientific usage, weight and mass are fundamentally different quantities", this editor is so full of the insight that Weight and mass are Not the same thing that the article was plastered over with {{Disputeabout}} and {{Expert-verify}} tags – which I've removed. The mere fact of mentioning (with a proper citation to a reliable source) that in some contexts people use the word "weight" when they mean the scientific notion of mass, or that sometimes "weight" is treated as a scalar instead of a vector, is apparently sufficient, in this editor's opinion, to warrant each section containing such a statement incurring these tags.

To 190: Whether you happen to think a certain statement is true, or not, is irrelevant – but if there is a reliable source containing the statement, that does entitle me, and any other editor, to "put it as a valid reference on wikipedia". Please read the Wikipedia policies, in particular Wikipedia:Verifiability, and pay attention to the very first sentence:

The threshold for inclusion in Wikipedia is verifiability, not truth—whether readers can check that material added to Wikipedia has already been published by a reliable source, not whether editors think it is true.

To everyone else: Please keep an eye on the article, so that it doesn't go back into a messy state like this version of May 19, 2010.  --Lambiam 05:58, 7 June 2010 (UTC)

A source is not reliable just by existing, thus not all sources are reliable. Leave alone when used sources are Internet articles published by associations that have not deep insight on the subject matter. Mentioning that people refer to matter properties by naming dynamic actions on that matter is not wrong (as it culturally happens) what is wrong is stating that such misconception is true and right (look, does it make sense?: Matter_Property = Effects_on_Matter_Property ?) i.e. p=mv yet momentum is not mass nor speed. —Preceding unsigned comment added by 190.28.86.153 (talk) 05:22, 8 June 2010 (UTC)

Yet if you are happy with your definition weigh means to measure mass, and you like Internet sources you can take a look at: [1]

I'm not going to edit more. keep the tag.190.28.86.153 (talk) —Preceding undated comment added 05:29, 8 June 2010 (UTC).

Older edit

refer to [2] for an article version (May 19, 2010) with less conceptual mistakes. yet very far from a good article as it lacks references and foot notes. yet it still had one portion on debate (but it is properly identified). Plus it lacks the meaningful ISO definitions.

Be aware that as of June 7, 2010 the latest community edit has significant conceptual mistakes:

-Differentiation between mass and weight[3]. -Differentiation between Pound-force and Pound (mass) units. -Molecular mass referred to as molecular weight statements.

Current Document tagging for factual accuracy has to be kept. 190.28.86.153 (talk) —Preceding undated comment added 05:07, 8 June 2010 (UTC).

Weight in general relativity

Apart from being too technical, the section In general relativity is also unclear (in my opinion) for readers who understand the mathematics underlying GR. In fact, the maths is actually trivial: it basically says, if you want to decompose a quantity E into quantities W and F, so that E = W + F, use W = (E − F). Ehm...yes. But then we are told that F must be chosen to be zero. Huh?

What exactly is the message? Isn't gravitational force a fictitious force as well in GR? So what's with the separation into weight and fictitious force? That's like separating a cow into steak and matter. And what is meant by "where there are no fictitious forces by definition"? What definition? The definition of "preferred"? The text sounds more agnostic than is necessary. The word "arbitrary" in the phrase "based on an arbitrary choice" may give the wrong impression; all reference frames are equal, but some are more equal than others, and there may be very good reasons to prefer one choice over another. And while it may be true that in theory all reference frames are equivalent, this need not mean that we can't discern components in the distortion of spacetime geometry and ascribe them to causes, for example a certain radially symmetric pattern to the presence of a large mass.  --Lambiam 08:54, 9 June 2010 (UTC)

"where there are no fictitious forces by definition" means that the fictitious force is defined to be zero in the preferred reference frame, i.e. ${\widehat {\Gamma }}_{\mu \nu }^{\lambda }=0\,$ in that frame. But, not being a tensor, it becomes non-zero in other coordinate systems. On the other hand, weight being a real force transforms like the various other real forces when changing coordinates.

Gravity is not fictitious. But the distinguishing characteristic (equivalence principle) of the real gravitational force is that it cannot be separated from fictitious forces (e.g. centrifugal force and Coriolis effect) in a unique way.

For example, suppose you look at our solar system and set up a Sun-centered inertial frame within which all the celestial bodies of the solar system move (to the first order) according to Newton's laws. One can define the weight of those bodies relative to that reference frame. If one transforms to another coordinate system, say Earth-centered, then one can distinguish the weight of the Moon from the centrifugal and Coriolis forces on the Moon due to the Earth's revolution around the Sun. However, someone else might choose to use an inertial frame tied to the center of the Milky Way galaxy. In this frame, there are additional contributions to the weight of the celestial bodies in our solar system due to their attraction to other parts of the galaxy; and there are additional contributions to the fictitious forces due to the revolution of the solar system around the center of the Milky Way. But something remains the same, namely the total inertial force on the Moon in the Earth-centered system which is still the sum of the weight of the Moon and the fictitious forces on the Moon. JRSpriggs (talk) 19:24, 9 June 2010 (UTC)

Perhaps a better way to look at it would be — all inertial force is a manifestation of gravity including the so-called fictitious forces. Thus the attempt to separate weight from the fictitious forces is a waste of time. That is, neither weight alone nor fictitious force alone has any meaning. Only the sum, inertial force, is meaningful. JRSpriggs (talk) 00:37, 10 June 2010 (UTC)

Is gravity a fictitious force? Many years ago I did a course in tensor algebra and this was one of the topics that was discussed. My recollection is that in the general relativity model, one did not have gravity - instead one had what can loosely be called a "curved universe". Martinvl (talk) 05:25, 10 June 2010 (UTC)

I guess it depends on the exact definition you use for "fictitious force", but the general lore is to call gravity a fictitious force in general relativity. Typical arguments are that in GR "free" particles follow geodesics, suggesting that there are no "real" forces working on them and that you can always choose a local frame in which the Christofel symbols vanish. I'm sort of curious what your argument is for saying that "gravity is not a fictitious force". TimothyRias (talk) 08:14, 10 June 2010 (UTC)

When I say that gravity is not fictitious, I mean that it is real. It is not merely an illusion created by a poor choice of coordinates. If it were such an illusion, then there would be another coordinate system (which covered the whole universe) in which $\Gamma _{\mu \nu }^{\lambda }=0\,.$ However, there is no coordinate system which abolishes the inertial force everywhere.

There is a difference between: (1) being able to zero the inertial force at any event you choose, and (2) being able to zero the inertial force everywhere simultaneously. The first can be done. The second cannot. This means that the inertial force cannot be localized in a way that is coordinate independent, unlike all other forces. But it is still a real force. JRSpriggs (talk) 05:55, 11 June 2010 (UTC)

Have you guys lost all perspective? I am referring to this God-forsaken section:

---

In general relativity

A point particle in free fall obeys the equation

${\frac {dp_{\mu }}{dt}}=\Gamma _{\mu \nu }^{\lambda }p_{\lambda }{\frac {dx^{\nu }}{dt}}\,$

where p_μ is the momentum 4-vector and Γ^λ_μν is the Christoffel symbol (which is the gravitational force field). Any separation of the inertial force on the right hand side into a part which is weight and a part which is fictitious force must be based on an arbitrary choice of a preferred reference frame where there are no fictitious forces by definition.

$\Gamma _{\mu \nu }^{\lambda }p_{\lambda }{\frac {dx^{\nu }}{dt}}={\big (}\Gamma _{\mu \nu }^{\lambda }-{\widehat {\Gamma }}_{\mu \nu }^{\lambda }{\big )}p_{\lambda }{\frac {dx^{\nu }}{dt}}+{\widehat {\Gamma }}_{\mu \nu }^{\lambda }p_{\lambda }{\frac {dx^{\nu }}{dt}}\,$

where the first term on the right side is the weight (gravitational force, a tensor (except for the dt)) and the second term on the right side is the fictitious force (a non-tensor which is zero in the preferred reference frame). The hatted Christoffel symbol is defined by using the Minkowski metric in the preferred reference frame rather than the physical metric used by the regular Christoffel symbol.

---

I note this doozy: “Any separation of the inertial force on the right hand side into a part which is weight and a part which is fictitious force must be based on an arbitrary choice of a preferred reference frame where there are no fictitious forces by definition.”

First, the whole article gets slapped with {dispute-I disagree-fatual accuracy-whine}-tags, as well as that particular section. Thus, the community was left with undecipherable garbage where the editors responsible for it couldn’t even agree amongst themselves about the fictitious forces of a fly-fart on a particle in a relativistic frame of reference. Are you kidding? The above material is so far beyond the scope of the subject of “weight,” it is truly absurd. Earth calling you guys: This article is about weight. It may be appropriate to digress into F = ma and Equations for a falling bodies. But this section is way beyond the scope of this topic (and readership level).

You two can exercise your “smartness” battles on Christoffel symbols (which gets only 100 hits per day, many of which are probably due to poor unfortunates curiously clicking on links to see what they will be taken to) or some other equally remote backwater. The above material has no place in this article, which is clearly intended for a general-interest readership. Greg L (talk) 19:01, 12 June 2010 (UTC)

I realize that only a few readers will get anything from this section (that is why I put it last). However, Wikipedia is supposed to serve all audiences not just one class of people.

When I looked at this article, I felt that there should be at least one correct statement of what weight is in the article. Gravity does not act on mass per se; it acts on energy and linear momentum, and also depends on their movement. And the gravitational force field is not just a spatial vector "g" with three components, it is the Christoffel symbol which has 40 components.

Why do you consider the sentence about separating weight from fictitious force a "doozy"? It is a simple statement of the truth in the equivalence principle.

There should be a place for the truth in this article. JRSpriggs (talk) 06:40, 13 June 2010 (UTC)

I agree with User:JRSpriggs to the extent that weight in a reletavistic setting should be discussed somewhere in Wikipedia. The current article should reference it and explain in layman's terms, what it really means and if posible describer it in terms of the Perihelion precession of Mercury. I have not looked at other articles on general relativity, so am not willing to comment atthis stage as to the appropriate home for such an article. Martinvl (talk) 09:59, 13 June 2010 (UTC)

Seriously, gents. A plain-speak treatment of the effect of relativity on weight might be suitable here. But the übur-advanced, undecipherable (to 99.9% of this article’s readership) techno-treatment like this belongs over at General relativity or Special relativity. That’s where readers intent on finding material with this level of difficulty will be looking. Now, I’ve seen that the editors who cybersquat over at those two articles think they’ve got it All Figured Out©™® and can imagine why you might not want to tread there. But that’s a good thing, IMO, because in this case, where you guys couldn’t agree whether it might be better to put the this symbol (the unpronounceable symbol for The Artist Formerly Known As Prince) before or after the $\Gamma ^{\lambda }$, the extra discipline imposed on you by having to go over there to vet your material will enforce rigor with whatever the holy hell it is you are arguing about. Greg L (talk) 14:21, 13 June 2010 (UTC)

Greg, your aggression is uncalled for and detrimental to constructive discussion. That being said, I agree that the section as it was, was to technical and written with too much jargon. Even with a good grasp of the subject matter, it was somewhat hard to figure out what point was being made. An the other hand, I also agree that something should be said about relativity and in particular the role of the equivalence principle in this article. I understand the point [[User:JRSpriggs|JRSpriggs] was trying to make with the paragraph. I'm still not sure I completely agree with it (but I think our difference of opinion in the end boils down to a matter of taste with respect to the definition of a fictitious force.) If a source can be produced that treats weight and fictitious force in this was, it should be possible to include a section that is written in such a way that it is at least somewhat understandable for someone without a background in GR. TimothyRias (talk) 08:10, 14 June 2010 (UTC)

“Agression”? Sorry. No aggression intended; just straight-talk. The editors here (whom I respectfully addressed with “gents”) are smart big boys and can handle the shock of that without the “gee gosh golly” facade of editors tripping all over themselves to be as inoffensive as possible. Moreover, I’ve seen far too many editors hide behind the apron strings of seeming to be a middle-of-the-roader when, in fact, they have made up their mind and are pushing an agenda.^Disclaimer Far too many of our articles are nearly useless because they comprise nothing but this sort of material, which is often lifted right out of 300-series math text books. As I stated above, a plain-speak treatment of the effect of relativity on weight might be suitable here. Fewer than one in a thousand readers coming to Weight would understand that “relativity” section as it was written. That outcome flouts the most basic elements of Technical Writing 101.  Readers seeking out such advanced material will look elsewhere where they would expect to find material like this. Greg L (talk) 14:24, 14 June 2010 (UTC)

At least, I think we need to say: (1) that the inertial force depends not on the mass m, but rather on energy E and Ev and Evv; (2) give a link to an article on force in general relativity (but I do not know of one at this time); and (3) say something about the equivalence principle. After all, light (which has no mass) is deflected by gravity. Indeed, light passing the Sun (moving perpendicular to the radius) is subject to twice the acceleration that a dust particle (at rest) at that location would suffer. JRSpriggs (talk) 07:18, 15 June 2010 (UTC)

May I remind JRSpriggs that photons do in fact have momentum - de Borglie equation states λ=h/p where λ is the wavelength, h is Plank's constant and p is momentum. In non-relativistic mechanics, momentum is equal to mv. However, I think that discussing this in an article on weight which is aimed at the layman is over the top. There is however nothing wrong with an introductiory paragraph that leads the reader to another article that could be entiled "Weight and Relativistic Mechanics" or something of that ilk. I however do not have sufficient knowledge of relativty to write such an article. Martinvl (talk) 07:47, 15 June 2010 (UTC)

To Martinvl: Of course photons have momentum ${\vec {p}}={\frac {E{\vec {v}}}{c^{2}}}\,.$ What made you think that I thought otherwise? One cannot correctly apply non-relativistic equations to photons. Mass in the context of special relativity is $m={\sqrt {{\frac {E^{2}}{c^{4}}}-{\frac {p^{2}}{c^{2}}}}}\,$ which is zero for a photon. JRSpriggs (talk) 08:08, 15 June 2010 (UTC)

In order to be relevant to this article, we need a source discussing the weight of light. Remember that this not an article about gravity, general relativity or light, but about weight. If nobody has ever bothered to write down a discussion about the weight of light, then wikipedia obviously should not break with that tradition.TimothyRias (talk) 08:49, 15 June 2010 (UTC)

Poking my head in here reminds me of Keanu Reeves in Speed, when he poked his head down through the access hatch to look under the speeding bus, took a look at the bomb, and said “F**k ME!” We have a talk page on the subject of “weight” and someone just pointed out about photons having momentum (doesn’t that underlie the principle behind solar sails? Even I know that) and also mentioned the de Borglie equation. I think you have overlooked the perfambulator of the modal states when they are juxtaposed with the plasmonic stator. So clearly Einstein didn’t have a full explanation. Greg L (talk) 04:59, 16 June 2010 (UTC)

To Greg L: If you cannot stick to serious arguments instead of sarcasm, then please go away. JRSpriggs (talk) 08:20, 16 June 2010 (UTC)

No. It was a valid point in the form of mild sarcasm with humorous intent. Lighten up and please don’t presume to tell me how I may think or how I may express my thoughts.

First off, Talking over the heads of the readership. Wikipedia’s articles are for communicating encyclopedically. As in all technical writing, communicating above the heads of the readership is verboten. This sort of subject matter has no place in this article. Your continuing to debate this nonsense here instead of on one of your talk pages—or on General relativity—leads me to suspect you are still interested in either showing off how smart you are and/or are still thinking it is appropriate material for this article, which it isn’t. The General relativity article has sections titled

4 Consequences of Einstein's theory

4.1 Gravitational time dilation and frequency shift

4.2 Light deflection and gravitational time delay

4.3 Gravitational waves

4.4 Orbital effects and the relativity of direction

You need to get this aspect of relativity’s effect added as 4.5 Effect on weight to this list, where relativistic treatments properly belong.

Secondly: Original Research. Your ruminations here suggest what you are up to is pure WP:OR. Just looking at you guys debate this (where you aren’t refuting the positions of others by citing reliable sources but are engaged in primary scholarly debate where one editor points out “photon momentum” as if the other is supposed to scratch his Ph.D. beard and exclaim “you’re right” and step forward to the greaseboard), leads me to suspect that the editors over at Talk:General relativity might stomp you guys flat over WP:Original Research if you were debating over there. It doesn’t surprise me that you came here where you could fly under the radar.

It’s about time that you guys start pointing out where reliable secondary sources are saying that Einstein’s papers state that relativity affects weight and this is somehow a phenomenon that is distinct from a simple Lorenz transformation on matter’s mass (multiply by γ and be done with it). Then it’s a simple matter: copy the formulas from those articles exactly as they are written and do so in the proper section of a relativity-related Wikipedia article. Your debating here about the formulas and “fictitious forces” instead of arguing about which source to cite is a sign that something was way wrong here.

The section I deleted (In general relativity) that used to be in this article didn’t have one single citation buttressing what was being alleged. Then I come here and find you guys engaging in primary mathematical debate as to whether a damned formula is proper instead of arguing via dueling citations. That will not happen again.

There, I said precisely what was on my mind with no sarcasm. Happy now? Greg L (talk) 20:04, 16 June 2010 (UTC)

For a discussion of the weight of light outside Wikipedia, see Lev. B. Okun (1989), "The Concept of Mass", in the section ’Gravitational mass.‘ A. di M. (formerly Army1987) (talk) 10:26, 14 July 2010 (UTC)

Weight is usually denoted by a lowercase w

I usually see weight denoted using a lowercase w; evidently the rational behind this is that a capital W is commonly used to denote mechanical work. —Preceding unsigned comment added by 81.132.198.81 (talk) 17:39, 12 October 2010 (UTC)

I don't recall any particular symbol in universal use for the weight. In my experience, most often it's just denoted mg. A. di M. (talk) 18:33, 12 October 2010 (UTC)

Units Table

w=mg : Correct let's do basic operations on it: w/gc=mg/gc which would have obviously units of mass but is not the weight

now this interesting table shows something like w=mg/gc which, not even knowing anything about physics, makes it a total mistake, and we know for sure it is a mistake because weight is not mass, Horrendous Mistake !!! it's unacceptable for an article that is meant to be accessed publicly.

It is necessary, therefore, to either correct the table, or get rid of it altogether —Preceding unsigned comment added by 41.223.4.33 (talk) 18:09, 21 December 2010 (UTC)

I am going to kill all references to apparent weight in this article!!

It's got to be done, and nobody has done it. So, per WP:BOLD I'm gunna do it.

For those of you who don't remember how this started, some misguided person started an article on apparent weight without having a really good definition for it (since there isn't one used in physics texts and reliable sources). Then the link to apparent weight started getting inserted into THIS article. Before long we were being told there was a difference between apparent weight and weight. It goes like this: I'm in an elevator and the cable has just snapped, putting me in free fall. My apparent weight is now zero, as the scale under me says. But that's not my REAL weight, which is the same as before..." This is all wrongheaded physics. It also suggests that your "weight" in any inertial situation, from vomit comet to space station, is NOT zero, even though your apparent weight obviously IS zero (which is why they call it weightlessness, don't you know). Wrong, wrong, wrong.

Your weight, according to ISO, is given by W = -m a, where a is your proper acceleration. Since proper acceleration is the same as g-force, your weight is also your mass times the g-force accceleration you feel, but (as always, as indicated by the minus sign) is in the opposite direction to the g-force acceleration direction (since this is an action/reaction pair of forces). Generally, it's what the scale under your feet says, although scales can be fooled in various silly ways, and we should not let that undermine our physics. If your cousin Joe is surreptitiously putting a toe on the back of your bathroom scale to make you look 10 pounds heavier (your apparent weight is higher!) that's not a matter of physics, but of instruments being misused.

${\vec {W}}=-m{\vec {g}}$ Where the vector-g is the g-force.

SBHarris 22:25, 25 December 2010 (UTC)

What?

I can't decide if this article is pure gibberish or just written so badly as to be just completely worthless. As a Ph.D. in engineering with 30 years of industrial experience, I can honestly say that whatever it may intend to be this article is, well, crap. —Preceding unsigned comment added by 192.158.61.140 (talk) 14:47, 18 January 2011 (UTC)

On behalf of the editors here, thank you very much! Some of the history of the problem may help to explain why things are complicated. There is an article called apparent weight that got started to "explain" why things weigh less in elevators that are accelerating downward, and more on elevators accelerating upward. That led to a long discussion which led to this article having to explain why such weights are honest-to-god REAL weights, not apparent weights. Then there is the problem of explaining why things have no weight (are weightless) in falling elevators, or in the orbitting space shuttle, even though obviously still affected by the acceleration of gravity in both cases. So all these problems are connected with a fairly subtle point in physics-- one that was still bothering Einstein in 1911, as you may know.

Anyhow, rather than complaining about it, can you suggest a few fixes that will make this article simpler, and yet still correct? Simply removing stuff led, in the past, to abominations like the article on apparent weight. If you don't understand "weight," you cannot tell why things are "weightless" in orbitting spacecraft (or weigh more as the rockets are launched), or why "apparent weight" is not a good article. You see the problem? SBHarris 20:58, 18 January 2011 (UTC)

BTW, I see that somebody has added two simpler introductory sentences to begin the LEDE. This is an improvement before we get to the nitty gritty. Good! SBHarris 07:18, 7 February 2011 (UTC)

Surely the standard definition of weight is simply the force due to gravity. Are you saying that an object in freefall has zero weight? I don't think most physicists would say that. I would say that objects in a falling elevators (space shuttle, etc.) appear weightless, but I would not say they have zero weight. (I am a univeristy physics lecturer, by the way) Timb66 (talk) 11:55, 7 February 2011 (UTC)

Sure, the standard definition of weight is simply the force due to gravity, and when you are in freefall, you measure zero force. Falling objects don't just appear weightless—they are weightless, and have zero weight in their own frame. So it's just a matter of careful wording. DVdm (talk) 12:12, 7 February 2011 (UTC)

sorry, I don't agree. I would say 'weight' ios the name we give to the force on an object due to gravity. And the force due to gravity is still acting on a falling object (which is why it is accelerating). Would you say the force on an electron due to an electric field is zero if the electron is allowed to accelerate freely? I would not, and the same is true for the gravitational force. Can you suggest any physics textbooks that support your position? I am at home now but will check the books in my office tomorrow. Timb66 (talk) 12:19, 7 February 2011 (UTC)

Yes, 'weight' is the name we give to the force on an object due to gravity. And force is relative. Books: see for instance Bernard F. Schutz' "Gravity from the ground up" and more with this little search. DVdm (talk) 12:55, 7 February 2011 (UTC)

Here's a few more modern (and one less modern) views of some of our heavy weights:^(NPI)

• Feynman, Richard P. (1963). Lectures on Physics", Vol. 1, Addison-Wesley. ISBN 0-201-02010-6

Section 7-7, page 7-11: "Therefore, Gagarin or Titov would find things "weightless" inside a space ship;"

Section 9-1, page 9-1: "Weight and inertia are proportional, and on the earth's surface are often taken to be numerically equal, which causes a certain confusion to the student. On Mars, weights would be different but the amount of force needed to overcome inertia would be the same. We use the term mass as a quantitative measure of inertia, and we may measure mass, for example, by swinging an object in a circle at a certain speed and measuring how much force we need to keep it in the circle."

• Ohanian, Hans C. (1989). Physics, Second Edition. Vol. 1. W.W. Norton & Company. ISBN 0-393-95748-9. Chapter 6, page 128:

"This means that in such a freely falling reference frame the gravitational pull is apparently zero; the weight is apparently zero. [...] Nevertheless if the driver insists on looking at things from his own reference frame, he will judge the weight of the apple, and also the weight of his own body, as zero."

• Hewitt, Paul G. (1998). Conceptal physics. Addison-Wesley. 8th edition. ISBN 0-321-00971-1. Chapter 8, p. 149:

"We define the weight of something as the force it exerts against the supporting floor on the weighting scale. According to this definition, you are as heavy as you feel; so in an elevator that accelerates downward, the supporting force of the floor is less and you weigh less. If the elevator is in free fall, your weight is zero (Figure 8.7) [...] Consider an astronaut in orbit. The astronaut is weightless because he is not supported by anything (Figure 8.8). [...] On the other hand, if the astronaut were in deep space far removed from any attracting objects, but his spacecraft were being accelerated, he would have weight."

• Taylor Edwin F., Wheeler, John Archibald. (2000). Exploring black holes: introduction to general relativity. Addison Wesley Longman. ISBN 0-201-38423-X

"Newton's first complicated explanation of weightlessness: As viewed from the center of attraction, every particle in your body experiences an equal "gravitational acceleration." Different parts experience the same inward acceleration. Therefore there is no relative acceleration between adjacent parts; the bonds holding your body together feel no tension or compression. They feel nothing. You feel nothing.

Newton's second complicated explanation of weightlessness: As viewed from your accelerating reference frame, every particle in your body experiences two equal and opposite forces. First force: gravity, directed toward the center of attraction. Second force: centrifugal force, directed away from the center of attraction. In your acceleratin frame frame these two forces balance, so each particle in your body feels zero net force. So does each nearby particle. There is no stress on the bonds holding your body together. You feel nothing.

Einstein's simple explanation: In orbit you are in a free-float (inertial) frame. A frame can be in free float even near a center of attraction. In a free-float frame you float freely, feeling nothing. Period."

• Hartle, James B. (2003). Gravity, an introduction to Einstein's general general relativity. Addison Wesley. ISBN 0-8053-9662-9. Section 6.2, page 111

"The modern version of Einstein's observer falling from the roof might be astronauts freely falling around the Earth in the space shuttle (See Figure 6.3). The astronauts are "weightless" [...] In effect, the gravitational field vanished in the freely falling frame of the space shuttle."

DVdm (talk) 19:29, 7 February 2011 (UTC)

Yep. User:Timb66, as a university physics lecturer it is crucial that you understand the point that a weightless man in a falling elevator or an orbiting spaceship doesn't just appear to have no weight. He really does not have any weight (to first order in a ship, neglecting tidal force "weight" that tends to pull him gently one way and another if he's not at the precise center of mass point within the ship; in a falling elevator this tends to gently try to pull him apart, and is no problem unless he's falling into something like a black hole). The insight for Einstein is deep: that which disappears and cannot be measured, even in theory, perhaps does not exist. So Einstein had the "happiest thought of my life" as he termed it-- the equivalence principle that finally led to a theory of general relativity that included gravitation. In a free fall frame the major component of the gravity field that gives you weight, disappears. In your inertial (free fall) frame, it is not there. It's not that you can't measure it. It's GONE. Only the second-order tidal components resulting from divergance of the field remain. SBHarris 19:41, 7 February 2011 (UTC)

Firstly, please do not patronise me. I mentioned my profession since it is relevant. Most of the references above are books on general relativity. This is a very subtle point, because in the framework of GR gravity is not a force, and therefore it is meaningless to define weight as the force on an object due to gravity. Weight is only really a useful concept in the framework of classical physics. And in that framework, most textbooks agree on the definition. For example: Young & Freedman, University Physics (12th edition) says 'The gravitational force that the earth exerts on your body is called your weight (p. 108) and An astronaut on board a space shuttle ... is in a state of apparent weightlessness ... True weightlessness would occur only if the astronaut were infinitely far from any other masses, so that the gravitational force on her would be zero.'(p.394). Other textbooks on my shelf have similar statements (Hecht "PHysics", Serway and Beichner "Physics for Scientist and Engineers"). One quote above that agree with your position and not mine is the book by Paul Hewitt. I do not have a copy of this book, I will try to find one.

Note also the search above is on 'weightless'. We have to careful, since in physics 'weightless' is generally an abbreviation for 'apparently weightless'. Being (apparently) weightless does not mean having zero weight. The above quote from Feynman is incomplete. Here is the full text:

• It is a fact that the force of gravitation is proportional to the mass, the quantity which is fundamentally a measure of inertia-of how hard it is to hold something which is going around in a circle. Therefore two objects, one heavy and one light, going around a larger object in the same circle at the same speed because of gravity, will stay together because to go in a circle requires a force which is stronger for a bigger mass. That is, the gravity is stronger for a given mass in just the right proportion so that the two objects Will go around together. If one object were inside the other it would stay inside; it is a perfect balance. Therefore, Gagarin or Titov would find things "weightless" inside a space ship; if they happened to let go of a piece of chalk, for example, it would go around the earth in exactly the same way as the whole space ship, and so it would appear to remain suspended before them in space.

Timb66 (talk) 00:11, 8 February 2011 (UTC)

Feynman in the above is adopting the Newtonian view in which weight IS due to a "force of gravity." He knows better, of course, but he's trying to make it easy for the students at that point. The problem is that making it easy now means you must "unlearn" things later, so that if you do this, you end up trying to define "true weight" vs. "apparent weight" NOW, and it all gets really complicated later when you find out there is no difference to Einstein. Thus, things in free fall near a gravitating body (like in the Space Shuttle) must be said (in Newtonian terms) to only be "apparently" weightless, not really-really-honest-to-God weightless. Worse still, what do you do with the weight caused by coordinate acceleration and inertia, such as your "weight" in a rotating space station, or your weight in an accelerating rocket? Are these true weights or just apparent weights? Is the force that squashes you into jam in both cases, a "real" force, or just a "fictious force"? (Some student asks: maybe you can ignore it, if it's only fictious??). In the end, it's all sort of mad keeping track of which things are supposed to be "real" and which "apparent" even though they do the same thing, and no experiment can tell the difference between inertial forces and gravitational reaction forces (given a non-divergent gravitational field at least-- and even then the differences are high-order). Some textbooks might choose to go there, having students learn Newton's view of gravity first. However, Einstein's view is actually a lot simpler, as he has only one kind of weight, and that's the one you feel on your feet, and the one your scale reads, period.

Indeed, you can forget gravity being a "force" or even causing a "force" if you define force as something you measure with a scale or force-meter, and "weight" as the reaction force acting against the force of the floor in your office that produces your proper acceleration through space time. And the same is true of the force from the floor in the rocket, the force from the floor in the centrifuge space station, the floor in the elevator, and so on. And mixes of all situations, like an accelerating elevator. One concept, one force action-reaction pair, all very simple. About all that's left is for somebody following Newton's thinking to make it a lot more complicated, by adding "fictious" forces here and there, and "apparent weight" from them, here and there, without any regard to what instruments like spring scales actually measure.

For example, the astronauts on the space shuttle referring to the same phenonena as Feynman, call the tidal forces "microgravity." But if you believe in Newton, the shuttle is only far enough from the Earth for 10% of gravity to disappear from distance, so what they really must mean is "APPARENT microgravity." Right? Yuck. Does the Vomit Comet airplane produce a few moments of zero-g-- or just a few moments of apparent zero-g? SBHarris 01:35, 8 February 2011 (UTC)

I think you are making a simple concept far too complicated. Feynman would be rolling in his grave! To make a start on improving this article, I have edited the opening sentence. In particular, I have removed the statement that the object must have come to rest against another object. Anyone who wishes to reinstate that will need to give a reliable source. Timb66 (talk) 02:58, 8 February 2011 (UTC)

You're right about the "rest." However, explanations should be made as simple as possible, but no simpler. Since weight isn't just created by gravity, and since gravity alone does not create weight (only a mechanical force can cause weight), I modified it to: "In physics, weight is the name given to the mechanical force exerted by an object, when it is being pushed away from, or being supported against following, a natural path of free fall." Often gravity is involved, but not always. And again, gravity cannot be felt. Only the force of mechanical RESISTANCE to gravity (or resistance to inertia) can be felt. Falling objects are weightless (have no weight). I think think despite your few sources, there is broad agreement on this. And while you say I'm making a simple concept far too complicated, you didn't answer my questions about what we're going to call weight and apparent weight, real forces and fictitious forces, and so on. All that is thrust upon us by Newton's suggestion that gravity creates an (unfeelable) force. But nobody feels the force of gravity; they feel the force of the floor. That's ultimately why gravity acting alone does not produce weight. SBHarris 03:29, 8 February 2011 (UTC)

I am sorry, but Wikipedia is not the place to invent definitions. It is not up to us to decide what is and is not thrust upon us. We have to consult reputable sources. I have a shelf full of university-level physics textbooks, and they all agree. For example, they all say that weight is the force on an object, not the force exerted by an object. As much as I agree with some of your sentiments, we have to go with the sources. And not books on General Relativity (I have those, too), nor what we think Feynman might have meant to say. I know you mean well, but in its current state, this article is basically useless to anyone wanting to understand what physicists mean by the term weight. Timb66 (talk) 05:30, 8 February 2011 (UTC)

I am sorry, but the most reputable source for definitions of erm, weights and measurements, is the ISO, not your university textbooks probably written by people not thinking very carefully. The ISO definition is in this article, and it agrees exactly with what I put into words:

In the ISO International standard ISO 80000-4(2006), which is a part of the International standard ISO/IEC 80000, the definition of weight and remarks concerning that definition are given as W = mg where m is mass and g is local acceleration of free fall.

That does not necessarily concern "gravity," nor should it, since you can have weight in a centrifuge or an accelerating rocket, both far from any gravitating mass at all (no gravity). Your weight in a rocket can only be thought of as the force ON you, if you wish to consider weight the fictitious force that arises from you being in an accelerated frame, but at rest. Which is not incorrect, but resort to fictitious forces as concepts is not really necessary, here. And even if you do it, you still need to say why these fictitious forces are the same kind of forces as this (also fictitious) "force of gravity" that supposedly acts "on you" when you're near a mass. Why put the reader through all that fictitious Newtonian stuff, when we don't need it? As for books on general relativity, they would be preferable for some of this, since GR is our best theory of gravitation. However, since weight arises from more than just gravitation, it's even better to come up with something inclusive. The "local acceleration of free fall" is numerically equal to the proper acceleration of the object. Understand that, and for free you get access to weight, g-force, specific force and on. And you see what weight is about, and it's about more than just gravitation. The "local acceleration of free fall" (times the mass) is the magnitude of the weight. The minus sign is to change the direction, since weight (as a vector) is the reaction force to the force that produces proper acceleration. SBHarris 06:43, 8 February 2011 (UTC)

The points we have been making are discussed in some detail in the physics teaching literature, most notably 'The American Journal of Physics' and 'The Physics Teacher'. I have downloaded a few articles (using our university library subscription) and would be happy to email them to anyone who is interested. Sbharris, is it ok if I send them to you? I think they will be very helpful in this discussion. Timb66 (talk) 11:30, 8 February 2011 (UTC)

Sure, you can send them to sbharris@ROMAN9.netcom.com where the Roman9 is replaced by IX. However, the person you have to convince here is not me, but all the other editors. Weight isn't just a matter of gravity, and you certainly need to qualify your first sentence. For the full definition, "weight" is one half of the action-reaction force-pair that accelerates a mass out of an inertial or free fall trajectory. If you insist on looking an an accelerated object (the only sort that have weight) in the accelerated reference frame attached to the object, THEN weight is the sum of the various fictious forces that oppose the force that accelerates the mass out of an inertial trajectory. These fictitious forces (gravity, inertia) being introduced by necessity in such a frame, in order to keep the object at "rest" (WRT the accelerated frame). The idea that weight = mg where g the g-force, or the acceleration of free-fall in the frame of the mass, is also an exact definition. I don't really know how else to say this, that isn't simply wrong. SBHarris 22:00, 8 February 2011 (UTC)

Rather than emailing them, I have put a bunch of papers here. One very useful summary of things is the letter by Morrison. It is very clear that there are two definitions, essentially equivalent to the two being discussed here. I tend to agree that the minority definition advocated by you is more sensible, but unfortunately we do not get to decide. We are not supposed to decide which is better, or to say that one is wrong, we are supposed to present them and give the published arguments in favour of each. I propose to modify the article to make it clear there are two definitions in use. In this way, the article will become much more useful and hopefully also much clearer! I hope you will join me in this effort. Timb66 (talk) 23:28, 8 February 2011 (UTC)

Well, I certainly agree with Iona and Bishop, who point out that nobody ever "feels" the force of gravity, and both agree with the ISO definition, and one says further that weight in all cases can conveniently be described as "what your bathroom scale measures." A definition I also have no problem with (perhaps we can lead with it: weight of an object in any circumstances is what a spring scale measures). As for the rest, with the stuff about objects in an orbiting space shuttle being described as "apparently weightless" but not "really-really weightless" I think it's a problem of a certain bunch of physics teachers-- how much in the majority or minority they are, I cannot say (do you really know??). In the space shuttle, the bathroom scale would read zero. The ISO definition of weight would say zero (we neglect tides and microgravity, as always). The proper acceleration and g-force are zero. Einstein would say zero. Meisner, Thorne and Wheeler would call the shuttle's cabin a "free float frame" (inertial reference frame) and say weight there is "zero." I'm shaking my head that anybody else should think otherwise, but some of your colleages apparently do. What can I say? Except that we don't call this environment "weightlessness" for nothing.

If you're going to attempt a second definition, you're going to have to call it "apparent weightlessness" or "effective weightlessness" and I really think you're in the minority, there. Morrison claims he's with the majorty by appealing to the American Heritage Dictionary, which even he admits has a first definition that no physicist would agree with (Morrison claims majority by cherrypicking the second definition). Right there we see an error by picking a non-scientific dictionary to define a science concept. But even the second definition is not a clear definition, though Morrison seems to regard it as such. The dictionary says weight is mass multiplied by "The local value of gravitatonal acceleration." Unfortunately, there is no such thing, as relatively teaches. The "local value" (meaning the value right here) is not enough information, since all it does is specify a place, like an elevator. An elevator does not have a "local value of gravitational acceleration". This value depends on the observer. The gravitational field only has a value in regard to a particular REFERENCE FRAME, which means for a paricular observer with a particular motion. Neither the American Heritage Dictorary or Dr. Morrison answer the question of the observer. In fact, the question of who the observer is locally, takes us right back to the original question, so the dictionary is no help. Not that we'd expect it to be. So I call "foul." SBHarris 00:16, 9 February 2011 (UTC)

You make some good points, but it remains true that the great majority of physics textbooks adopt the gravitational definition. (Even the book by Hewitt quoted above (I found a copy) actually uses the two different definitions in different places!) The paper by Galili 2001, which is quite long, makes this point while also agreeing with you that the operational definition is better. Please have a look when you get the chance. Timb66 (talk) 03:59, 9 February 2011 (UTC)

Well, I read the paper by Galili and (after the pre-Einstein history, which is interesting) all it does is cause embarassment for the profession of physics teachers. Some of the quotes he gives (the sum of all gravitating bodies in the universe) are (as he points out) worse than Newton's understanding (as usual, Newton turns out to be fairly subtle). Galili does indeed make my points and argues for an operational definition of weight, so that orbiting astronauts are finally just weightless, not "weightless" with air/scare quotes, or only apparantly weightless. Also, as we've noted, the removal of weight by means of bouyancy and the removal of weight by means of coordinate acceleration (as in a descending/accelerating elevator) are quite different things, as the elevator changes the net force on the person, but bouyancy does not (it merely redistributes it and may displace it away from the scale, but the person, as when floating in water, is still fully supported by the same total force as in vacuum, and not is not at all weightless in the same sense as in a free-falling elevator). Nor are astronauts in the neutral bouyancy tank weightless anymore than if they were on a waterbed. But in the international space station, they are. I'll finish on the mass vs. weight page. SBHarris 06:05, 22 February 2011 (UTC)

The local gravitational field??

LEDE now says:

In most physics textbooks, weight is the name given to the force on an object due to gravity.[1] [2] However, some books use an operational definition, defining the weight of an object as the force measured by the operation of weighing it (that is, the force required to support it). Both definitions imply that weight is a force and that its value depends on the local gravitational field.

I'm still waiting for an answer to what the "local gravitational field" is. Since this must vary locally by the Lorentz frame of the observer, there has been the suggestion that this "local gravitational field" we rely on for "weight" must be the one in a frame at rest with respect to the nearest mass. But what if we have a second mass (like the moon) that isn't at rest with respect to the first one? Do we ignore it? In other words, does having the moon overhead affect your weight, yes or no, according to this definition? The definition says you weight less on the moon (close call) but I suppose it doesn't matter if the Earth is overhead. We're already told being in earth orbit does not make you weightless, according to this definition (you only feel weightless). I believe we already decided that (as with being in orbit) motion does not affect this definition, so if your elevator starts to accelerate downward and you feel lighter, or you're at the equator and your sensitive scale shows you lighter with respect to the pole, neither of these are true decreases in "weight" according to this definition. So what is it that the scale measures, and you feel? It seems the answer is that the scale opperationally measures apparent weight, not the weight, if you don't use the operational defintion. Your TRUE WEIGHT in this conception, is what a minority of lower level physics books say it is (not that there's any evidence that any of them thought about this general problem, very much).

So-- is this alternate definition going to go into our lede?

I suppose it would be POV if I split it out as JUNIOR HIGH DEFINITION?

By the way, as a technical matter of sourcing, the Galili paper mentioned to back up the statement in the lede, doesn't exactly say what it is used to imply. Indeed, Galili offers such a statement by ANOTHER author which does split out the two definitions used in our LEDE. But the conclusion is offered with some surprise on Galili's part, as indicated by Galili's insertion of emphasis into the quote. Galili says this: <blockquote=Galili>Eisenkraft and Kirkpatrick (1995) reflected on the subject as follows: Many [?!] physics teachers carefully distinguish between the force of gravity and the weight. Weight is the reading on the bathroom scale, or the support force needed to keep you at rest in the non-inertial reference system. Other teachers use the term ‘apparent weight’ to refer to the scale reading and use weight to refer to the force of gravity (emphasis added). Galili adds the emphasis. To me, this indicates that Galili really doesn't buy the idea that most physics teachers have thought about it much, and that most really do not make the distinction that the lede in THIS Wiki-article advocates. Eisenkraft and Kirkpatrick think they do. Galili evidently doubts it. So who are we to believe, and who do WE follow? Did Eisenkraft and Kirkpatrick do some statistics on some large number of texts of a certain level? I doubt it. So did Galili, but couldn't say so politely. But I'm willing to be convinced. Galili was not. SBHarris 19:30, 8 March 2011 (UTC)

It is not clear what point you are trying to make.TR 09:18, 9 March 2011 (UTC)

• Even if it were true, we'd have to decide what level of education these texts are aiming at. The definition implied is not general, and in some cases gives us real problems, as it doesn't predict the weightlessness of astronauts in orbit. Should it remain as our lede definition just because many lower level texts define weight in this bad and non-general and non-experiential way? (even if they do, which I do not admit); or in Wikipedia should we use the general definition in the LEDE, which is also the ISO definition (which defines weight as simply the measured proper-force exerted by a mass against a scale in the weighing frame)?
• There's plenty of room later in the lede, and in the atticle, to talk about the simplifications that (may) need to be introduced for beginning students. For my part, I could live with the article starting as defining weight as the force that a mass exerts against a scale, due to any cause-- period. Then, you may need to separate out the forces due to mechanical reasons (bouyancy and other mechanical pushes and pulls) from the "fictious forces" that don't show up in Newton's third law, and are due to geometric acceleration, either from gravity or coordinate acceleration.
• We can put in the fact, somewhere in the lede, that non-moving "free" objects (not mechanically pulled up or pushed down) sitting on the surface of a planet, have a weight that is MOSTLY due to gravitational acceleration where they are (we still have centrifugal effects). But that's a lot of qualifiers,and it needs to be followed immediately by the note that if any of them are wrong, the weight will not be this value. SBHarris 19:18, 9 March 2011 (UTC)

You have written "I do not believe the first sentence of this article is true. Certainly, the two references given do not support it. " In fact, the reference do support this, please read them more carefully. I have most of the textbooks on my shelf, so I can vouch for it. The majority do indeed use the definition given in the first sentence. I know you do not agree with the definition (and neither does Galili, one of the authors of the references), but Wikipedia is not the place to argue the point. You need to write your own book or publish a scholarly article. By chance, Galili is visiting our department (School of Physics, University of Sydney). I hope to talk to him soon. Timb66 (talk) 22:22, 9 March 2011 (UTC)

That’s nice. Perhaps you can ask him why, if he intended his survey of textbooks as a scientific or scholarly study, he didn’t present his conclusion with statistical confidence limits. I’m serious. I think he’ll tell you the obvious. At least Morrison with his small sample didn’t pretend that it was anything other than a demonstration that applied only to his sample. Neither of these men would suggest using their conclusions inductively to apply to “textbooks” as a generalization, or even (I suspect) introductory college textbooks, the population from which they drew the sample they examined. The first sentence not only ignores more advanced textbooks by relativists like Hartle and Taylor, it fails even to establish that the defnition of “weight” should be gleaned from introductory textbooks in the first place. It fails on every level, from premise to method to data collection to misuse of other people’s conclusions. Actually, it’s YOUR original research, and I don’t like it.

You say that I should write a paper? Here’s what I would write from these references:

The pedagogical definition of the term “weight” at the college introductory physics level, has been debated. Morrison [4] reported that when he examined 11 textbooks sitting on his own bookshelf that were “the usual collection of examination copies sent by publishers to college physics departments,” that within them the most common definition of “weight” was the force of gravity on the object produced by the nearest astronomical body. Galili [5] stated that in an unpublished study conducted by himself [data not given] he drew “mainly, though not solely, on the physics textbooks published in the USA those [sic] that address the introductory physics courses at the level of college-university instruction.” (ref. 15). In this sample Galili found that “Despite the doubtful validity of the weight concept when defined as a gravitational force, it is widely presented in educational practice and physics textbooks.” He also reported that “only a small fraction of authors define weight operationally.” (ref 18)

"Only a small fraction." Of a secret list with no quantitation. But from it, a novel argument toward an inductive conclusion is drawn about weight, as it is supposedly defined in “most physics textbooks.” And that argument is done newly by you, here on Wikipedia, where this definition is used, with these citations, as the introductory sentence to the article on weight. And you want the other editors to go along with this? Have I got this correctly? And you're serious? SBHarris 04:26, 10 March 2011 (UTC)

Galili says:

Despite the doubtful validity of the weight concept when defined as a gravitational force, it is widely presented in educational practice and physics textbooks.

In a note he adds the nuance that this statement is based mostly on American college level introductory textbooks. You might try to argue that "widely used" is not the same as "used in most", but later on he says,

Leaving aside the question as to why the CGPM’s decision to adopt the operational definition of weight entailed no changes in most teaching programs (a social phenomenon),...

From which we can safely deduct that he indeed really means that most textbooks use the gravitational definition. Trying to argue that this source does not support the statement that "most textbooks use the gravitational definition" is thereby just arguing against the facts. Spewing righteous indignation and accusing other editors of OR does not make you more correct. In fact, makes others less inclined to take you seriously.TR 09:21, 10 March 2011 (UTC)

I'm no physics lecturer but I have to agree with User:TimothyRias. The Galili reference does state that the gravitational force is widely presented in textbooks. The statement that it is in "most" physics textbooks is, however, unsupported by the references, or at least a stretch on their wording.

I suggest changing the first sentence to...

In educational practice and physics textbooks, weight is the name widely given to the force on an object due to gravity.

WikiDMc (talk) 15:59, 10 March 2011 (UTC)

I could live with a statement that said that most introductory college texts define weight as "so and so" although I'd continue to be unhappy at the source of this knowledge. Come on-- it's the anecdotal statement of one educator, combined with another educator's statement based on 11 random texts on his office shelf. He might as well be telling us about the dates on 11 pennies he pulled out of his pocket. It's very bizarre that we're arguing about "evidence" of this quality. And in any case, suppose both men had conducted an exhaustive survey of undergraduate physics textbooks (of which there are far more than 11) and given us statistics. And the two studies agreed with each other. All we'd have then is a knowledge of what college undergraduate textbooks say (and I'd be happy to include that with qualifiers), and we'd still be ignorant of what textbooks on relativity say. Or what the various regulatory bodies like the ISO have decided. It's all very murky. Personally, all this makes me suspect that the average college physics teacher has no idea what "weight" is, or should be. But the evidence is so poor that I can't even conclude THAT, at this point. SBHarris 22:14, 10 March 2011 (UTC)

If you want statistics you might want to look at Galili 2003 (referenced in the article).TR 22:48, 10 March 2011 (UTC)

The survey of 11 books is fairly complete. The number of university-level physics textbooks in widespread use is not much greater than that. Timb66 (talk) 04:19, 4 April 2011 (UTC)

You're kidding, right? Did you even attempt to go online to see if you're not talking out of your... ah, hat? [6] I didn't get past page 8 in this 25-per page list of "physics texts-for-rent" (thus current) before finding 22 general college or university physics texts in the first 200 book entries (yes, a lot aren't physics texts and a lot of physics texts aren't general, and there were duplicates, but 20/150 = 1 in 7 were different general texts). I got *bored* there, but feel free to look through the next 200 entries (in 75,000!) and see if you can find some more. Then, repeat ad nauseum until you realize the text-world is larger than you imagine. We already have: Hewitt, Young, Hobson, Serway, Wilson, Giancoli, Walker, Griffith, Halliday, Knight, Cutnell, Sandin, Kranskopf, Kirkpatrick, Richardson, Wolfson, Giambattista, Giordano, Bauer, Ostdick, Christman, and Labroo. Your turn. SBHarris 03:12, 20 April 2011 (UTC)

The point is, SBHarris, that you shouldn't be concluding anything, at least not here on Wikipedia. We can only cite references and Galili's work is a published source in a peer reviewed journal, so is a valid reference. If I pulled 11 pennies from my pocket, concluded that most pennies were made in 1984 and had the work published in the International Journal of Science Education then it too would be a valid statement to include in Wikipedia.

If you want to include a statement about how textbooks on relativity define weight then you will need to find a suitable reference. ISO, of course, can be referenced directly so I, and I expect most, would not object to including ISO's definition in the main article but not at the expense of other valid definitions (and by valid I mean supported by references; not what I conclude, you conclude, or anyone else's unpublished opinion concludes). WikiDMc (talk) 13:40, 11 April 2011 (UTC)

I'll be glad to turn that point around on you there WikiDMc. You shouldn't be concluding anything, at least not here on Wikipedia, either. At this point, you seem to have concluded that the best definition of weight is that which is contained in university and college texts, and that therefore that definition should LEDE this article. Well, do you have a realible source that this definition is the BEST definition? Not your personal opinion-- I want you to source it. I note that even the guy you quote who surveys the texts doesn't agree with the goodness of the definition himself, so you can't go to him. Okay, now whose personal opinions are running the show? Play by your own rules. SBHarris 03:36, 20 April 2011 (UTC)

I haven't concluded that at all, and I would appreciate you not using straw-man arguments. I haven't said that it is the BEST definition, only that it is a valid definition from the referenced sources, and I have even suggested that you could promote the ISO definition within the article but not to the detriment of other valid definitions.

I sense that this entire discussion was started because you believe the ISO definition should be given more prominence, specifically in the lede sentence or paragraph. I agree with that sentiment but looking back through this discussion, I don't think a single suggestion for how the lede should be rewritten has been provided, other than my suggestion for a slight rewording of the first sentence. I suggest that you provide a suggestion for how you think the lede should be written so we can discuss that rather than the quality or merits of works that have already been peer reviewed and published.

Lastly, I find your style of discussion with statements such as, "turn that point around on you," and, "You're kidding, right? Did you even attempt...," quite uncivil and suggest you read WP:GOODFAITH and WP:CIVIL.

WikiDMc (talk) 16:26, 20 April 2011 (UTC)

I'm not sure what you mean to say by "valid definition from the referenced sources." The two referenced sources are actually two papers in education journals that make the points that definitions in texts are inconsistent ("the need for consistent definitions"), or (in the other case) inconsistent, historically unstable, and sometimes still bad today ("weight versus gravitational force: historical and educational perspectives.") The sources referenced in this article complain about the unreliability of texts on this point (what purpose in writing in an education journal if all the texts are great?,) and they prove it by pointing out that texts are not consistent, therefore cannot be reliable, by that criterion alone. In addition, they point out that some text definitions are unphysical ("sum of all attractions from all objects in the universe" suggests that the moon affects weight, when that is not the case, as earth-moon motion removes all but tidal effects). The textbooks also seem at odds with the ISO definition and the working definition used by scientists who study weightlessness and microgravity.

This leaves us with a problem. The two citations that begin this article are used in an non-contextural way: they are mined for part of the conclusion of their writers about textbooks (the data part), but the rest of the authors' conclusions regarding the texts, are not mentioned. Thus, the first lede sentence implies (in part from its very position in the Wiki article) that the source of the definition it gives for weight is an WP:IRS "reliable source," which means one with a reputation for fact-checking and accuracy. However, that is not the case, since the two actual citations argue for the opposite about texts. IOW, there is a difference between the questions of whether the cites reliably report what texts say, vs. what whether those opinions are any good. We begin with a statement of what texts usually say, but fail to mention that the authors in the cites think they actually should say something else and that in any case, they say different things. This entire sentence is deceptive and needs to thrown out of the lede, or moved to the end to be used as a reference for an alternate opinion held by a fraction of general college texts, but deprecated by education journals, standards societies, and NASA alike (which facts should all be added as qualifiers). The operational definition, as the most widely used in science and industry (if not college texts) should lead the article.

Whether the operational definition reduces to the supposedly more common intro textbook definition depends on whether or not one holds that "the gravitational field" at a point is affected by a weighed object's motion at the point. This is not obvious! The lede, as now written, seems to assume that general into physics textbooks address that issue, but no evidence is given that they do. Does the same "local gravitational field" exist for the man on weight-scales in a motionless elevator, as it does in the same elevator that has just started to fall without brakes? Einstein says "no" (and that's why the scale gives a different number inside the elevator not suspended). Intro physics books are probably silent. Relativity texts and modern physics (not to mention the ISO) are all naturally on the side of Einstein. If the lede says anything on the subject, it should be on that side also. SBHarris 19:02, 20 April 2011 (UTC)

Please don't take this the wrong way but I think this is your most coherent post so far on this talk page and (after reading it only once) my initial response is that I agree with almost all of it.

If you can propose a concise lede I will probably support it, so long as potentially contentious statements (such as deprecation of college texts) are supported appropriately.

WikiDMc (talk) 19:36, 20 April 2011 (UTC)

This article needs a history section

This article is in dire need of a history section that discusses the historical development of the concept. This could help clear up several possible points of confusion, and provide some context for the rest of the discussion. In particular it would be a good place to note that with the introduction of GR, the concept of weight has become of little scientific interest. (Since it is clear that it cannot be viewed as independent of other inertial forces, and thereby is very frame dependent.) The 2001 article by Galili actually gives a fairly decent overview of the historical development going back to Greek philosophy. It could serve well as a basis for such a section here. Unfortunately, I currently do not have the time to write such a section. (May get around to it later). It would be great of somebodyelse would pick this up and write that section.TR 09:47, 10 March 2011 (UTC)

"Weight" defined operationally as a force between two objects (the object, and the scale that gives you the weight of the object) has none of these problems. It tells a person what they feel on their feet. As such, it's not frame-dependent, but is a Lorentz invariant, so it's very much like space-time interval between events, the invariant mass, or any other invariant quantity in SR. It is the "proper force," the magnitude of the four-force. It is produced by the mass of the weighed object and its proper acceleration, also known as g-force, imposed on it by the scale. All these concepts are well-known from relativity.

One cannot go to a person on a falling elevator, or centrifuge, or rocket accelerating in space, who is standing on a bathroom scale and say: "You know, in another inertial frame, you wouldn't weigh that much." He'll (she'll) just say "What do you mean? If I take my trusty bathroom scale to the other frame, maybe I wouldn't, but that comes with the job and I could feel the difference, too. So? As long as the scale is in MY inertial frame, which is the one that interests me, observers in all other frames see it read what it reads. It's an instrument, for heaven-sake. And besides, that's also the weight that I feel on my feet, so it's all good." The ISO's weight defined as mass mutlipied by the instantaneous acceleration of free-fall in the fame of the mass, is exactly this operational definition.

As for "inertial forces" (and any other "fictious forces") since we don't (can't) measure these with instruments, we don't care so much about them (true), but "weight" is something we do measure, and do feel. That which crushes you into strawberry jam if it's too large, is not observer dependent (as though some observer in another frame sees you not-crushed). Weight is not a fictious force, but a good-old-fashioned mechanical action-reaction force. How you want to EXPLAIN it, and why you're not reacting to it with some type of acceleration, differs from Einstein to Newton, from view-to-view, and from observer-to-observer. It's sort of your personal business, so long as you acknowledge that the force you measure, is actually there. The fact of the force itself (the one you feel) doesn't change, and in that sense, it's objectively "real," no matter whose physics you believe, and what frame you observe it from. SBHarris 22:02, 10 March 2011 (UTC)

I'm not sure who you are trying to convince of what (I think we all agree, that the operational definition is better, this is however irrelevant to this article), but this rant does not seem to respond in anyway to my suggestion (that there should be a history section).TR 22:46, 10 March 2011 (UTC)

What do you put in the "present" section? We can't put that "weight" is now irrelevent. It is relevant. Astonauts are weightless in the orbiting space shuttle. I can see they are. They know they are. All instruments say they are. If this article is correct, the only people who don't think they are, is some fraction of writers of introductory college physics textbooks! That's very sad! Do you really think it should go into the introduction of this article?? SBHarris 22:51, 10 March 2011 (UTC)

Does that matter for the history section?TR 22:56, 10 March 2011 (UTC)

No-- on that, we agree. However, you introduced the idea of a history section above by saying that "in particular it would be a good place to note that with the introduction of GR, the concept of weight has become of little scientific interest." That isn't true, so far as I can see. I think it's more true that the definition that "weight is the name given to the force on an object due to gravity," is now what has become of little scientific interest. In other words, the definition that starts this article, is the one that is now of little scientific interest!

The space shuttle mission specialists and ISS crew, after all, spent a big fraction of their time investigating the effects of weightlessness and near-weightlessness on human physiology, and biological and physical systems. Google Scholar gives 26,000 hits on "weightlessness," and although some of them are on "simulated-weightlessness," none of those involve being in Earth orbit (they are all things like being in bed). Science papers don't call zero-g or micro-g in orbit "apparent weightlessness."

There is no force due to gravity in the space shuttle (though it's well inside the Earth's gravity field), and what Einstein teaches is the view that there's really no force "due" to gravity anywhere. Including when standing still on the surface of Earth, minding your own business. Gravity doesn't cause force; gravity causes geodesic motion in curved 4-space. You may resist such geodesic motion with a force, but if you do, then THAT is the force. It's not due to gravity, so don't blame gravity for it.

So any history section needs to note that the concept of weight and weightlessness has not gone away with relativity, because the ideas of "weight" speak to the idea of forces that you feel, and these still objectively exist in anybody's physics. If anything, the concepts are stronger than before, and include the idea that the weightlessness felt in inertial motion is as real as any other kind of weightlessness. Also, there is nothing "artificial" about the weight that is the reaction force to a mechanical force (ultimately, a set of electromagnetic forces) that cause you to be coodinate-accelerated, as in a rocket or centrifuge where the floor pushes on your feet (one atom pushes on another atom that is too near it). It may be fun to think of this kind of acceleration as a sort of "artificial gravity," but there's no reason to think of the force you feel as a sort of "artifical weight," unless you have a way to tell what sort of weight is "really-real-honest-to-god-weight." That last is a sort of Platonic idea which does not survive modern instrumentalism, nor should it. SBHarris 01:42, 11 March 2011 (UTC)

It is great that you can argue that their should be scientific interest in weight, but the fact is that there has been almost no interest in weight as a physical concept in the past century, as is exemplified by the almost total lack of scientific (physics) publications on the subject. The interest is so low that the physics community has not even attempted to provide us with a definition. _{Note that there has been considerable scientific interest in the concept of weightlessness outside of physics, for example on its effect on living systems.}TR 08:15, 4 April 2011 (UTC)

The "physics community" does not provide physics standards and definitions, anymore than happens in chemistry (IUPAC) or astronomy (IAU). Nomenclature is not primarily a scientific act, but a political one (albeit one that must make scientific sense). ISO/IEC 80000 provided a definition of weight in 2009 and as the latest international official declaration, that is what we should use. The idea that we should let a majority of college physics texts define a basic physics word for us, is ridiculous. Nobody has argued for that in the literature (not even the people analyzing physics texts), and the idea that THIS article should do so, has come out of some editor's personal preference. College texts have their problems when it comes to defining scientific words, and no articles have documented these, more fully than the ones being used here to push these texts, as a source of definitions for physics wikis! That's very fishy. SBHarris 17:18, 20 April 2011 (UTC)

Unclear quoting style in "ISO definition" section

The "ISO definition" section contains the line:

In common parlance, the name "weight" continues to be used where "mass" is meant, but this practice is deprecated. "

Is the quote at the end of this line a typo, or does it indicate the end of a literal quote from an ISO definition? If the latter, the whole quote needs to be set off more clearly. 86.160.219.84 (talk) 13:48, 8 June 2011 (UTC)

Excellent point. According to this post, it appears literally in the 1992 edition of ISO 31-3. But we have it in the ISO 80000 section, and since ISO hides everything behind paywalls I can't verify that it really made it into that version. So I don't know what to do. Hans Adler 15:12, 8 June 2011 (UTC)

Yeah, it's a pain. Admittedly I am not the one who has to balance their budget, but to me the idea of an international standards organisation not making its standards freely available on the internet is ludicrous. 86.181.201.14 (talk) 21:09, 8 June 2011 (UTC)

Going back through the history of the article, it is clear that that piece of text (minus some editorialization that was added later) was supposed to be a verbatim quote from the ISO definition. I've ecplicitly formated the text to inidicate this. Somebody still need is indeed the verbatim text of the ISO definition.TR 08:41, 9 June 2011 (UTC)