Talk:Mass versus weight

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weight v mass[edit]

It's always assumed that weight is proportional to mass. But is it exactly? Ignoring buoyancy, when accurately measured, does all materials have the weight we would expect for its mass. Ie. Is gravity effecting all mass exactly equally?

Seb-Gibbs (talk) 08:17, 14 October 2010 (UTC)[reply]

In the same location, at the same time, ignoring extremely minor differences due to the shape of the two objects being weighed, magnetic effects and electrostatic effects, or the fact that by lifting a large object to weigh it you are changing the Earth's properties... yes, according to Newton's laws of Gravity. Someone with a better understanding than I of Einstein's General Theory of Relativity may like to make comment on whether proportionality still holds.

You may also be interested to read 13 Things that Don't Make Sense by Michael Brooks. A quote from Chapter 2, "Maybe Newton’s law of gravitation, the law that describes how their trajectories should be playing out, is in need of an overhaul."

David. 161.51.11.2 (talk) 10:58, 17 February 2011 (UTC)[reply]

This is an ongoing experiment,^[1]^[2] but so far, within the very small uncertainty, they are the equal. This goes back to Eötvös_experiment but there are more recent attempts, for example, to compare aluminium and gold. Gah4 (talk) 15:35, 6 May 2017 (UTC)[reply]

References

^ "One hundred years of the Eötvös experiment". link.springer.com. Springer-Verlag. Retrieved 6 May 2017.
^ "Laboratory Tests of Gravitational and sub-Gravitational Physics". www.npl.washington.edu. University of Washington. Retrieved 6 May 2017.

Billiards on the Moon[edit]

re the billiard balls on the moon. I am a complete layperson but i assume that gravity on earth would increase the friction so the decreased friction on the moon would mean that the balls broke and moved more swiftly, although falling into the pockets more slowly. Any experts there who can answer this question? 89.241.254.21 14:54, 9 November 2007 (UTC)[reply]

F<=uR is a good approximation for friction (u should be 'mu', the coefficient of friction). In this case, the maximum friction F on a billiard ball would be lower on the moon because the reaction R would be lower, in turn because the weight of the ball would be less. It should be noted that other effects (e.g. lack of drag due to lack of atmosphere) also come into play. In future, Wikipedia:Reference_desk may be able to answer your question. Hope this helps. Sheffield Steel^talk_stalk 16:32, 9 November 2007 (UTC)[reply]

The balls would also be much more inclined to rebound out of the pockets. A “Moon-grade” billiards table would probably have much enlarged pockets to compensate for this. Of course, all of these are subtleties that go far beyond the basic principal being conveyed. And technically, during a break shot, where the racked billiard balls are typically touching each other (or at most a few millimeters away from each other), the opportunity for meaningful differences in friction to come into play as the kinetic energy is distributed is effectively nonexistent (except for the speed of the incoming cue ball). The racked balls’ initial behavior would be very similar to that kinetic demo game where six steel balls hang from strings and “click-clack” back and forth. So, no, they would not ‘break with more swiftness’. Indeed though, they would do better on the Moon at retaining the finite kinetic energy (speed) the farther they got from their racked positions due to less rolling resistance; as Sheffield pointed out, the magnitude of this effect can be calculated. As for air friction, I was imagining the game being played on the Moon indoors in a shirt-sleeve environment (what do astronauts on a Moon base do in their spare time?). Greg L (my talk) 20:25, 9 November 2007 (UTC)[reply]

oops :-) Serves me right for answering the question in vacuo rather than reading the relevant part of the article and getting the context. Sheffield Steel^talk_stalk 20:51, 9 November 2007 (UTC)[reply]

That nasty bouyancy[edit]

While the section on bouyancy is nice, the next paragraph right after claims that a doctor's scale measures actual mass. Presumably it means conventional mass? Or perhaps it's alluding to the fact that the precision is so bad for that scale that it doesn't matter? If so, qualifiers are needed.

Even worse is the next paragraph which claims that lunar scales balances would work the same as on Earth. Yes, if both are in vacuum, but only then. Even if you put them both in atmosphere (say, compare scale-weight on your moon-base), you're not going to measure the same mass-number unless you're weighing two things of equal density, or else you happen to have the density of your atmosphere in your base about 6 times that of Earth-normal (as the ratio of g's), to compensate for the reduced weight-error produced by bouyancy produced on the moon. Achh! More qualifiers needed. But I thought I'd better bring it up here so you can decide what you want to do. I'll add a bit on the problem of measuring unknown masses in air to micro-precision. S B H arris 06:19, 1 February 2008 (UTC)[reply]

The point being made about dual-pan devices like doctors’ scales is that if you move them from the equator of Earth to the poles, you aren’t going to have any change on the measured value. However, a single-span spring scale that reads 100.0 kg at ±50.5° latitude, will read 99.795 kg at the equator and 100.139 kg at the poles. These differences are due to the differing magnitude of the centrifugal force of Earth’s rotation. So spring scales technically and truly measure force. Dual-pan scales, like doctors’ scales, are true mass comparators. Of course, few scales are accurate to a tenth of a percent. And the article makes it clear that these are technical differences—not practical ones after a scale has been calibrated.
I revised the offending paragraph so it no longer uses the Moon as an example in order to avoid mixing possible buoyancy effects into the equation. I had actually intended the Moon example to form a mental picture of an indoor example of a moon lab (shirtsleeve environment, with air and all)—same as the billiards example. So I changed the example to one of moving a dual-pan balance from the equator to the poles of Earth. Greg L (talk) 21:10, 29 September 2008 (UTC)[reply]

Mass, weight, and the effects of gravity[edit]

According to Einstein's theories of relativity, mass changes with acceleration(e.g., infinite mass at light speed). Also according to the aforementioned theories, gravity is functionally identical to acceleration. Therefore mass should change with a change in gravity. Is there something I'm missing here? Skylerorlando (talk) 01:50, 2 April 2008 (UTC)[reply]

Yes. Mass changes in relativity according to velocity, not acceleration (they are different things). And you don't get infinite mass at light speed because you can't get to light speed. And even the mass change as you get close to light speed is a function of inertial frame (ie, of the viewer), and so in some sense is not "real" (see mass and mass in special relativity). By "real" I mean it's not something that all observers agree on, and the change it makes in the gravitational field of the object, is mostly to distort it rather than to make it "bigger" (that is, it gets stronger in one direction, but weaker in another, and it can't cause the object to collapse into a black hole). See mass in general relativity. For this reason, most physicists have stopped calling this mass increase a mass increase, and prefer to say that the mass does NOT increase, but the energy and momentum do. The more "real" mass which all observers agree on, in special relativity, is called invariant mass, and it does not change with velocity. S B H arris 05:23, 2 April 2008 (UTC)[reply]

Scales and historical use of weight[edit]

There is something rather amusing with having an article on weight vs mass finish off with a section featuring a balance scale and asking what it measures. It of course measures what *today* we call "mass". But a thousand years ago, we didn't call it mass - we called it "weight" because the term mass hadn't even entered the language, and using a balance scale-type device was about the only reliable way we had then to measure the mass/weight of anything.

Now let's set up this hypothetical scenario: go back in time a thousand years, pluck some unfortunate merchant with nothing but his scale and weights and bring him forward to the present. Then send him to the moon with his equipment. Give him some moon rocks and other items to measure. He'll tell you what they "weigh" in relation to his weights. Bring him and all the same items back to the Earth and have him measure them again. He of course is going to give you the same answers, telling you that they "weigh" exactly the same as they did on the moon. He might tell you that they "felt" a lot lighter, that they were easier to pick up on the moon, and so on, but he is not going to tell you that those items weigh only a sixth on the moon what they do on earth. He's not going to understand why they (and himself) felt lighter (or not as heavy) on the moon, but he is also not going to think their weight is any less. Indeed, if you tried to tell him that they weighed a sixth on the moon what they do on earth, he'd probably think you were trying to swindle him. No one else from his era would agree to accept one sixth the payment for produce or goods on the moon just because it all felt lighter because it's still the same amount of stuff that weighs the same as on Earth

Now we can't say they're wrong - it's their language and their concept of weight, after all. What's wrong is we, and in particular the sciences, sometime in the last three centuries, decided that weight no longer meant weight and that a new term, mass, would replace what weight had hitherto meant and that weight would now come to mean something it never had: a force.

If all this isn't enough, the section also talks about a spring scale and what it measures. It measures something that we've only been able to measure for a relatively short period of time: gravitational force. Yet we call this "weight", the same term that has existed for centuries as if our merchants of a thousand years ago were spending their time measuring gravitational force (Lord only knows with what). And nowadays the preferred unit provided by these scales is the kilogram - a unit of mass. The mind boggles at the ironic stupidity of it all.

So cut the arguing; weight = mass = weight. Weight is not a force. That's a recent change of definition that makes no historic sense. It's the old (and common) term for mass and the two should be treated as the synonyms they still are by most people.

As to what to call "weight", i.e. gravitational force? Try "heaviness". Objects are one sixth as heavy on the moon. It fits with everyone's understanding of the role of gravity in altering the force required to lift a given object. D P J (talk) 06:40, 17 January 2010 (UTC)[reply]

Wow. I don’t know where to begin. You are entirely wrong on all counts.
Quoting you: But a thousand years ago… and Now let's set up this hypothetical scenario: go back in time a thousand years, pluck some unfortunate merchant… and What's wrong is we, and in particular the sciences, sometime in the last three centuries… Irrelevant; thousands of years ago, there were four elements: earth, air, water, and fire; science marches on. In science—today—mass is an inertial property and weight is a force.

Period.

Quoting you further: [A spring scale] measures something that we've only been able to measure for a relatively short period of time: gravitational force. Hmmm… it depends on how one defines “short period of time.” How about “since at least about 1850,” which is so far back, the second law of thermodynamics was just being discovered.
Quoting you: As to what to call "weight", i.e. gravitational force? Try "heaviness". Good for you; you’re getting close (but backwards). According to Websters “weight” is defined as follows:

weight: relative heaviness, the force with which a body is attracted toward the earth or a celestial body by gravitation and which is equal to the product of the mass and the local gravitational acceleration

Note the word “force” in the above. So, “heaviness” is used to help define and describe “weight” in science. I’m an engineer. The discipline of engineering has terms like “weight loading.” I haven’t come across the term “heaviness loading” (although a Google search turned up two hits, one of which referred to body building and lifting weights). Note too that masses in orbit are considered to be “weightless,” not “heavinessless.”

I suggest you go get the rest of the world to adopt your suggestions such as “heaviness loading.” Why? Because Wikipedia reflects the way the world really works as evidenced by modern reliable sources and doesn’t try to lead by example with bright ideas like those you have advanced here.

Note too that Websters defines mass as follows:

mass: the property of a body that is a measure of its inertia

…which is the proper scientific definition. And then Websters adds this bit:

…and that is commonly taken as a measure of the amount of material it contains and causes it to have weight in a gravitational field

…which is exactly what this article states about the common, non-scientific way people perceive the mass of an object (by its weight since gravity is so profoundly ubiquitous on Earth).

Quoting you: Weight is not a force. Sorry, but stating an absurd falsehood in only five, succinct words does not make it any less false; it only makes it look more foolish. You can take up your theory with the ISO. The standard ISO 31-3 (1992) defines “weight” as follows:

The weight of a body in a specified reference system is that force which, when applied to the body, would give it an acceleration equal to the local acceleration of free fall in that reference system.

There is also this from the National Physical Laboratory: What are the differences between mass, weight, force and load? (FAQ - Mass & Density), which states the following about the definition of weight:

Scientifically, however, it is normal to state that the weight of a body is the gravitational force acting on it and hence it should be measured in newtons (abbreviation N), and that this force depends on the local acceleration due to gravity.

Note that this Wikipedia article couldn’t possibly be clearer that it is discussing the distinction in the context of the physical sciences. Accordingly, with regard your allegation that “Weight is not a force”, the world of science says “Ahhh, gee… thanks, but no thanks.”

Nutshell alert: If you take a spring scale or gravimeter, calibrate it on Earth, and take it to the moon, it will show one-sixth weight, which is one-sixth gravity, which is one-sixth force. If you do the same with a knife-edge balance, it will show the same reading no matter what celestial object you travel to. Note that NASA routinely measures the mass of astronauts on the International Space Station by measuring their inertia on an oscillating sled. This article explains how the Body Mass Measuring Device works and how “weightless” astronauts still retain their “mass.” Please, no whining about the way the world of science really works and how it uses these words to maintain scientific rigor.

Quoting you one last time: The mind boggles at the ironic stupidity of it all. Fine, you established that you have really high self esteem. That doesn’t make your arguments any less false in the face of clear and copious evidence to the contrary. Greg L (talk) 16:35, 12 June 2010 (UTC)[reply]

Though I agree with your reply to the OP (of this section) pretty much, I think I get what the OP meant, to some extent, or the "heart" of it, perhaps.

At least, I have a much milder idea, conceived from reading the theoretical story he related, which I found to be somewhat.. provocative (of thought), at least in myself at that time, though I hesitate to use that word ("provocative") here because it's, I think, somewhat of a "fancy word," perhaps to such a level as to be be seen by some to be "pretentious" or "pedantic," and I'm not sure my statement about his theoretical story quite deserves such a treatment (at the same time, I do believe I'm over-thinking things), but technically (regarding dictionary definitions), it (the word, provocative) is apt. It fits the context. I'm sorry to have digressed.

I'm not a scientist myself, but I think there is somewhat of a point to be found in what he said, although he did call for actual scientific terminology change among other things that I also didn't entirely agree with.

I do think however that there is something to be said for his.. how should I put it, that thought experiment of the OP's, even though he arrived at (what I, and what it seems Wikipedia's scientific community (or at least the guy to whom I'm responding) seems to see as) untrue conclusions.

But my point anyway, which is gleaned from aspects of the OP's post, is something along the lines of:

While weight and mass are, scientifically speaking, different concepts, in the practical world, for most people it may be perfectly fine to treat them fairly synonymously, at least in many situations. For most intents and purposes, the scientific differences between the definitions of weight and mass don't matter to most instances of the common man, even up to the point that even if you were to, as he said, magically pick up a merchant from 1000 years ago (with only his scale and weights) and take him to the moon and back, it wouldn't make a difference, economically speaking. Of course, now isn't 1000 years ago, but a part of that point was based on the fact that a comparative scale (where you're deducing the weight of objects by comparing them with a standard weight or set of weights using a simple see-saw style of scale) will still get the same results on the moon, and it would still be considered (even now) that you have the "same amount of stuff" (i.e. the same mass) whether you're on the moon, Earth, or Mars, or the middle of space. So that would be one example where, as the OP might perhaps see it, "proves that weight and mass are the same thing" but really just means that it's one of many examples of instances in which, due to their close relationship, the weight and mass of something can be safely considered as being essentially the "same thing" in that instance, even though they really aren't, technically.

In other words, although weight is really the amount of force that gravity acts upon an object's mass, it is simple and practical to generally consider weight and mass to be the same thing in many (usually fairly non-scientific) contexts, at least as long as you properly understand the real differences between the definitions, and the basic laws of physics / motion, etc. - or possibly even if you don't.

Regarding that last thing, I might even reason (theoretically, again) that it could be possible that one (if intelligent enough but at the same time ignorant to the concept of the difference between weight and mass) could initially have merely an idea of "weight", but then independently form a (perhaps primitive) sense of a concept of "mass" (even if not recognizing that term) upon being taken to the moon and back as described in OP's post, and while there, told/shown that things weigh 1/6th their Earth weight there, figuring, whatever it is making the difference in weight, it's not changing how much stuff is there, because, well, it simply can't. Unless like.. David Copperfield or Jesus or someone is doing it (minor lol), and that what we know as "weight" must be a reflection of how much stuff there is (including reflecting how densely packed something is) (things in recent italics being of course references to mass or aspects thereof), and this reflection is due to some force one experiences while on a celestial body, which we now have (hopefully) learned varies (from one celestial body to another).

This (the intelligent but yet ignorant to "mass" person, and that person going through what was described here vaguely and in OPs post's hypothetical story, is all speculation on my part, but I feel like I could reason that someone smart enough (but ignorant to the concept of mass... that kind of person might be sort of hard to find) might perhaps be capable of learning the above on their own under the terms as described and in the ways described, if not something similar at least... Regardless it's beside the point and doesn't really matter.

My real point is basically a point that says: "within the context of X, A - which might seem to be the same as, but doesn't quite literally = B can often be safely assumed to = B for most, or at least many / some intents and purposes."

Anyway, with the main point, and really everything I've been saying, if I'm being "captain obvious", I duly apologize for wasting everyone's time, and I also apologize for TL;DR reasons.

tehmikuji (talk) 20:44, 20 June 2011 (UTC)[reply]

Bouyancy again[edit]

At risk of repeating the same remarks I made on TALK:weight, it is rather silly to simply say that "bouyancy" makes things weigh less, without some kind of qualification. Bouyancy makes things "weigh less," as measured by spring scales DIRECTLY UNDER THEM. But that is all. Nevertheless, their total weight is the same-- it is merely spread out over a larger surface area which isn't making contact with the scales. If it were making contact, you'd see it hadn't changed.

In short, "bouyancy" decreases weight in exactly the way any suspensition device does. A man in a harness partly supported by a crane, will weigh less according to a bathroom scale underneath him. But does he REALLY weigh less? His weight is simply transfered to the crane, and would be measured if that where on scales. We now come down to what we MEAN by "weight." Is it just what the scale right underneath us measures?

There's a photo in the article of an object, buoyed in a fluid in a graduated cylinder. Now, put that whole graduated cylinder on a scale. How much does the object weigh now? If it's floating, you'll say "nothing." But I promise you, that if you add an object to a cylinder of fluid on the scale, you'll get the same weight difference as you would if you simply put it on the scale directly. The reason is the scale now measures the entire fluid pressure, not just the downward force directly under the object. Similarly, the "bouyancy" decrease in weight, in all cases where you "see" it, is simply an instrument failure. S B H arris 19:39, 13 June 2010 (UTC)[reply]

I see your point. If one puts a scale under the earth’s entire atmosphere and then put the balloon into the atmosphere, the scale would read the full weight of the balloon. The same applies to mass standards, where they compensate for the 150 ppm difference due to buoyancy. Alas, it is too difficult to weigh the entire atmosphere of the planet. Nevertheless, I’m gonna go back and see if I can add more scientific rigor per what you wrote here. Greg L (talk) 03:48, 14 June 2010 (UTC)[reply]

P.S. (thinking aloud here). The qualifier is “it” weighs less. If you put a neutrally buoyant swimmer in a pool, the “the swimmer” (what you put on the scale) weighs nothing. Indeed, if you weigh the entire pool (or the entire freaking atmosphere of Earth), you will see that the fluid/object system exhibits the full added weight of the buoyant object. I’ll think about this nuance for a bit—maybe overnight—because I want to get this into it without that “he said / she said” flavor that quickly comes to articles that have been hacked on in a collaborative writing environment. The flip side of getting too aggressive with this point is that a 100-gram mass standard (those little ultra-polished stainless steel things) actually weigh 150 ppm less because of buoyancy. One could write this:

Really, the entire building surrounding the metrology lab and all the air inside the building weighs the full 0.980665 newtons heavier (and not 0.980518 newtons) when a 100-gram mass standard is put inside the building because the building supports the air and the air supports the mass standard. But you have to measure the building very quickly because a little more air will leak out of the building than leaks into the building and soon, ever-larger volumes of air supports the mass standard.

This effect comes out a Mythbusters show, where a sealed cage didn’t become any lighter after birds lifted off their perches and flew around inside. What is true is that buoyancy reduces the weight of objects. Your point is that buoyancy doesn’t reduce the weight of the object and the fluid supporting the object. It’s probably worth mentioning that. Gonna think a bit here… I think I can get this point across very simply. Greg L (talk) 04:13, 14 June 2010 (UTC)[reply]

P.P.S. Done. I think… (∆ here). Fifth paragraph down at Buoyancy and weight. Let me know if I missed the mark. Greg L (talk) 15:09, 14 June 2010 (UTC)[reply]

A better scientific definition of mass (?)[edit]

If it is indeed "better", should it not be the first definition mentioned? (See 3rd para of main article). David. 161.51.11.2 (talk) 11:13, 17 February 2011 (UTC)[reply]

Relevance of "that are not in perfectly accelerating free-fall"[edit]

The first paragraph of the article states, "weight refers to the force experienced by an object due to gravity." This force does not disappear if the object is in "perfectly accelerating free-fall", it is the reason for the acceleration, so what is the purpose of the caveat, "that are not in perfectly accelerating free-fall," in the first sentence of the second paragraph? WikiDMc (talk) 14:08, 18 February 2011 (UTC)[reply]

To answer BOTH the questions in the sections above, the reason the second definition is "better" is that it is correct and the first one is technically wrong. Weight is "due" to gravity only indirectly, when an object is not in free fall (for example, on the surface of the Earth). In that cause, the weight is due to the force that retards the free-fall (it's an action-reaction pair). In this case, provided by the scale.

In Newtonian dynamics the view is that objects in free fall don't loose their weight, and that is why they accelerate in free fall. The problem with this view is that it asserts that "weightless" objects in free fall (like in runnaway elevators or inside a "vomit comet" plane, or the space shuttle) really still HAVE a weight, but that nobody can measure it with any instrument (looking out the window doesn't count). In Einstein's mechanics, the reason objects in free fall have no weight is because they see no gravitational field (save for the second order tides).

Coming back to the basics, gravity does not cause "forces" that can be felt (I have $20 for anybody who has ever felt of the force of gravity). It's a fictitious force to "explain" a motion that we otherwise can't explain, but not a "force" that can be felt or measured or that affects a scale. We'd intuitively like "weight" to be what we measure with a scale, and gravity per se has nothing to do with that. Does that help? Objects on the orbiting shuttle are close enough to the Earth for gravity to still act on them, but they really are weightless (to first order--neglecting microgravity), not just "apparently weightless." S B H arris 21:52, 18 February 2011 (UTC)[reply]

Sorry, but we don't get to decide which definition is better, or which is wrong. We have to stick to what is in the textbooks and other sources (see weight and its talk page). And nor is this talk page a place to discuss the laws of physics, as much as we might enjoy that. Also, I don't see why a separate page is needed at all for "mass versus weight". Timb66 (talk) 11:50, 20 February 2011 (UTC)[reply]

I agree, I'm not sure this page should exist at all. But since it does, it should at least be correct.

As for gravity being a fictitios force, I'm not going to bite at that one.

If the first definition is technically wrong, then it should be corrected or removed. Also note that I was referring to the definition of mass, which is labelled as "better", not the definition of weight.

For the free-fall confusion; this article seems to re-state one of two definitions of weight from the weight page (force due to gravity), but the caveat of "that are not in perfectly accelerating free-fall" implies the second definition (force resisting gravitational acceleration). If the article does not treat both definitions, it should at least be consistent in which definition it is using.

WikiDMc (talk) 09:19, 21 February 2011 (UTC)[reply]

If we're talking about definitions set by the laws of physics, there's no way out of discussing the laws of physics! When it comes to sources, there are various grades of sources for science-words. I hope that when it comes to the physics concepts of work or energy, we don't rely on the standard dictionary, which may have common definitions that have to do with common use (where it takes a lot of "work" to hold a weight at a constant height, and there's a lot of positive "energy" in an enthusiastic crowd). For physics, we use science sources. As to textbooks, I hope we all agree that graduate level texts are better than university texts which are better than high school texts? If you're talking about gravitation, then Misner, Thorne and Wheeler is the source to beat.

As to why this page exists, I'm not at all sure. Probably the ultimate source of the problem is the Apparent weight page and the "apparent weight" concept when it comes down to weight that is supposed to disappear in inertial frames, yet still exist, in some Platonic fashion. This is the idea that things in inertial paths in a gravity field might be apparently weightless, but since they're still close to a planet, they're not really-really weightless. Since gravity still acts on them, goes this argument, they still have a weight, it's just that we can't measure that weight. That's out-of-date physics, like the planetary model of the atom (pedagogically maybe useful, but not even close to true). This particular notion has been outdated since 1911-1915, but here some folks are, still pushing it. It's fine to explain it as an approximation, and as the old Newtonian view, but it's not good to simply say it's as good a definition as any other. It's not as good a definition as any other, since it pretends that something "exists" (i.e. "weight" in an inertial frame) when it cannot be measured, and might as well be a spritual concept, since it is certainly not a physical one. It's not used by the ISO. If some textbooks haven't made it into the Einstein GR era now, after nearly a century, that's too bad. If the non-science dictionaries haven't caught up, that's really too bad, but that's not what they're designed to do.S B H arris 21:03, 21 February 2011 (UTC)[reply]

Misner, Thorne and Wheeler is certainly a great book if you want to learn about General Relativity, but please note that weight is a concept in classical physics and, as I pointed out on the talk page for weight, it is an obsolete conecpt in GR. There are over 1200 pages in MTW and I haven't checked them all, but I can't see anywhere where the word 'weight' is defined. (yes, I know they talk about weightlessness). If you want a definition of weight you need to stick to books about classical physics, which means undergraduate-level physics textbooks. Please understand that I do not disagree with your physics arguments, but Wikipedia is not the pace to push your point of view that the majority of physics textbooks have got it wrong.

And can we merge this article with weight? Does anyone disagree? Timb66 (talk) 22:16, 21 February 2011 (UTC)[reply]

Yes, yes, operational versus gravitational weight, blah blah... (Sorry, it is a valid discussion to have, just not on this page).

All I was trying to point out is that, no matter which definition of weight you use or believe to be correct, this article is not consistent. It defines the term weight and then contradicts itself. It also defines mass and then goes on to say, "hold on, here's a better definition!"

And yes, please merge with weight to do away with this abomination of an article.

WikiDMc (talk) 16:22, 22 February 2011 (UTC)[reply]

I have no problem with getting rid of this article (if there's anything in it that isn't in weight already, put it in). Also, could we get rid of the apparent weight article, too? I don't think anybody knows what "apparent weight" means. It's a poorly defined concept, like matter, with no agreed-on scientific definition.

As for "weight" the concept still exists in special and general relativity, but is renamed as "force" (it is the reaction force to proper force, which is the same as the four-force upon a mass in systems where mass is constant, which it should be, in systems where something is "weighed"). It is — mass X proper acceleration. If we're not going to use a "measured force" based definition of weight, then relativity has nothing to say about it, but so far as I can tell, you're not in the realm of science anymore if you now want "weight" to be something unmeasurable. Or want it to be the same as mass. So speak up, if that's the goal. In all the various textbook definitions of "weight" I've seen, there's one outstanding characteristic of the "bad" definitions, and that is that they don't say how you're supposed to determine the "weight" of anything, according to their definition! Suppose you want weight to be only "the force due to gravity" then how do you tell what that is? Suppose I agree with your definition, but disagree with what you say an object's "weight" is? How would we settle the disagreement experimentally? I'm afraid an "operational" definition is all we're realistically left with, if this idea of "weight" is to be a scientific one. Science is operational. S B H arris 01:27, 25 February 2011 (UTC)[reply]

I support also getting rid of apparent weight. One article on weight is surely enough.

Can you please give some sources for the above comments on weight in general relativity? And I do not think that the gravitational definition of weight, as put forward by most textbooks of classical physics, is any less well-defined than other concepts in classical physics. To calculate the weight of an object, we first measure the acceleration due to gravity at that location and then multiply by the mass of the object. And to measure the acceleration due to gravity at that location, we can release a test particle from rest (relative to the source of gravity) and measure its acceleration. Done. And notice that according to this definition, the weight of the original object does not depend on its motion (neglecting SR effects, of course). Timb66 (talk) 11:31, 25 February 2011 (UTC)[reply]

In the experiment you describe, how are you going measure acceleration of a "test particle" relative to a "source of gravity"? You can't do that except when you know your test frame (the one you measure the test particle's motion with regard to) is ALREADY at rest WRT a single source of gravity (like sitting on the surface of a non-rotating planet). Everyplace else (from the surface of a rotating planet to a descending elevator to the space shuttle in orbit), this experiment fails, because the motion of your test particle in a moving frame gives your frame's proper acceleration, not the local curvature of space due to gravity for an object at rest to the gravitating body, which this alternative view aparently regards as the only quantity that can confer "weight."

How would you measure "weight" aboard the space shuttle, for example? You'd have to calculate it, not measure it. No test particles could be involved. When you got done, you'd get a value about 90% that on the Earths' surface. That's a weird value and a weird idea (and besides, if you're going to just calculate it on paper, what do you need an experiment FOR?)

Furthermore, such a definition removes "weight" from describing the forces that people feel due to anything but gravity in certain very particular non-moving situations, including the effect of all inertial forces. Are we not to call the proper force that results from both gravitation forces and inertial forces, "weight", then? What? "Apparent weight", perhaps? See all the problems we get into? Are you sure you don't want the article on apparent weight back? S B H arris 20:20, 25 February 2011 (UTC)[reply]

In the experiment I described, you would measure the acceleration of the particle in a frame at rest with respect to the source of gravity. Note that in physics most quantities are defined in abstract terms (thought experiments, if you like), rather than by experiments that would actually be carried out. By the way, I invite you to replace the gravitational force in your statements by the electric force. But we are going around in circles. This is not the place to argue about whether physics books and other reputable sources have got it wrong. Our job is to report what they say, and also what is said in the various scholarly articles. Timb66 (talk) 10:22, 27 February 2011 (UTC)[reply]

You say: "By the way, I invite you to replace the gravitational force in your statements by the electric force." Answer: If by "electric force" you mean the force due to electromagnetism, ie, Lorentz force, it's no problem at all, since the Lorentz force is already fully Lorentz covariant/invariant (since that's what SR was originally invented to do), so the force is independent of whatever inertial frame the observer chooses. Thus, a moving charge X causes the same force on charge Y, as if charge Y were moving, and charge X were stationary (this involves merely a different inertial point of view). If you put your reference frame on the [weighing scale+object] (which obviously must be in the same frame if you want to do any weighing) then the force your scale measures is the proper force: the net force responsibe for the weighed object's proper acceleration (instantaneous acceleration away from 4-space geodesic = path of free-fall). Lorentz forces cause proper forces, of course, since they're invariant 4-forces. Proper force also automatically includes "fictitious" forces (both gravitational and inertial) if you're weighing in an accelerated frame. Gravitation in GR is Lorentz covariant also, of course. Equating weight with the (negative of) the proper-force (-mass times g-force) you feel, solves all these problems, since there's always only (only) one net force that you feel, and you and everybody else (as well as any scale you have traveling WITH you) agrees on its value. That's it.

Now, "in the experiment you described" I invite YOU to tell what your weight in any other definition would be, if you're moving with respect to TWO masses of unequal value. You're not at rest WRT to either of them, and they are not at rest WRT each other. Which single mass rest-frame do you now pick for your definition, or neither? And what does the number mean when you're done? Do you ignore the other mass? Or sum the effects of each masses on your position (pretending you're not moving) from THEIR (separate) rest frames? Unless you do something like this, that definition is now undefined, though there's no doubt that in many of such situations (any one in which you happen not to be traveling inertially), your scale would give you a number, and you'd feel a proper force between you and it, that you could use to walk or do anything else associated with weight. So now, explain that definition of weight for Wikipedia, since it's not defined in your sources, except in limited or obviously wrong ways.

Finally, it is most certainly NOT merely our job is to report what texts say (including bonehead text), nor even what is said in the various scholarly articles that summarize these things non-exhaustively (as they obviously must in a large topic like this). That's not a definable job which has a "correct" answer. If it were, it could be done by a machine. Indeed, it would have been done by all reviewers which would differ from each other only in grammar and style, not content. Thi involves human judgement, as is made obvious by the fact that different scholarly reviews (including in this matter) say quite different things. But if you the WP editor pick one review, you're doing original thinking and judgement, deny it or not. Likewise if you stop looking for reviews at 6 reviews. If you pick a longest review (Galili, say) you must still summarize it, and that also requires original work and leaving out material, deny it or not. Scholarly reviews are often far too detailed for WP, and must be cut. We, the editors, must cut them, and this is subjective. This epistemological problem is unescapable, and so your first step is to realize that it exists, not simply pretend that it does not (and so therefore presumably, your view of how we might write this article is a matter of objectively reporting sources, but mine is not). Sorry, this cannot be avoided nor wished away. The "arguing in circles" is a systemic fault, not my fault (and not yours, either). S B H arris 16:57, 2 March 2011 (UTC)[reply]

Delete this article (merge with Weight)[edit]

There seems to be consensus that this article should be deleted. I am not sure how to do this. Can somebody advise the procedure? or go ahead and do it? Timb66 (talk) 22:56, 1 March 2011 (UTC)[reply]

If you do it, make sure that there's nothing in this article that needs to be rescued. For example, I like the buoyancy section of this article better than I do in the weight article. Of course, you're going to get stuck again, since there really are texts that say that objects held up by buoyancy have less "weight." They'd say that with a balloon but not an airplane, even though there's absolutely no difference is the mechanism by which they don't fall. Both are held up by forces that counteract their weight on a scale underneath them, but in both cases are still transmitted to the ground. As well claim that a wrecking ball has no weight because it's held up by the crane. S B H arris 17:08, 2 March 2011 (UTC)[reply]

Since it is still here, I vote for it to stay. As people, even ones who should know, get it mixed up often enough, I believe that there is reason for this page. This is especially true in countries where pound is a unit of both force and mass. It isn't so easy to get wrong with kilograms and newtons. The actual physics could go to weight, though, as I noted on the talk page, this is still a research subject. Also, even more recently, related to dark matter. Gah4 (talk) 15:52, 6 May 2017 (UTC)[reply]

GIrl on swing caption[edit]

This is a convoluted way to illustrate the diff. between weight and mass, and seems misleading, but my main concern is that the caption creates the impression that the tension in the chain is a constant equal to the child's weight, which is false. There are other factors involved that muddy the waters, but I can't think of a new caption that would salvage the truth from the confusion this example creates.77Mike77 (talk) 16:57, 5 March 2013 (UTC)[reply]

The chain does hold all the child's weight (plus weight of the swing seat and chain). The child's weight increases when she accelerates, as in a centrifuge, and varies throughout her arc. The only way to consider that this is NOT true, is to use the moronic gravitational definition of weight propagated as one alternative in the weight article. You know, the one that insists that weightless astronauts on the space station must still have 90% of their weight, because the g field (for resting people) is 90% as strong where they are? In this definition, weight is not something a scale measures, but that you must calculate knowing the absolute value of the g field at some distance in the rest frame of the object producing it. It's an artificial number good for nothing, but some texts support it, mostly because they wrote their definition without considering the contributions to weight that may be made by motion. S B H arris 21:28, 5 March 2013 (UTC)[reply]

Try learning to read before posting more non sequiturs. I wrote "my main concern is that the caption creates the impression that the tension in the chain is a constant equal to the child's weight, which is false." If you think that the tension in the chain IS constant, then your understanding of physics is as deficient as your mastery of civil discourse. Weight is defined as the force of gravity on an object, and it does not vary up and down with every little random tug. Weight is a constant in a vector diagram, with magnitude "mg". Other forces may be involved, causing the vector resultant to vary, but the weight is a constant if "g" is constant. Your confusion is itself proof that the child-on-a-swing experiment is a disastrous example because it introduces numerous irrelevant factors that hide the important point. I realize that to someone dieting, "weight" is simply the reading on a bathroom spring-scale, and astronauts are " weightless" in that sense, but in physics terms, that's ridiculous. If a person in freefall has no weight, as you claim, then there would be no force causing them to accelerate downwards. Acceleration requires a force, sorry. 77Mike77 (talk) 15:20, 29 March 2014 (UTC)[reply]

Engineers and scientists understand the distinctions between mass, force, and weight.[edit]

The statement Engineers and scientists understand the distinctions between mass, force, and weight is presumably true, but I suspect that some get it wrong, anyway. This is especially true in the US, where pound is both a unit of mass and force. Some time ago at an air museum I found an airplane engine thrust specified in pounds, and then converted to kilograms. I suspect that there are many spring scales calibrated in kilograms. Gah4 (talk) 15:27, 6 May 2017 (UTC)[reply]

Yes, there is "kilogram-weight", which is the gravitational force on a mass of 1 kg. I've never seen a bathroom scale calibrated in newtons. (Technically, they should be calibrated in newtons, but since the mass is proportional to the weight, it makes no practical difference.)77Mike77 (talk) 18:10, 10 November 2018 (UTC)[reply]

As long as it is in your bathroom, that should be true. Take it to the moon, and I disagree. I suspect that the calibration is still close enough at the top of a tall mountain. Gah4 (talk) 21:26, 31 July 2019 (UTC)[reply]

See Kilogram-force. The kilogram is a widely (albeit incorrectly) used measure of force in the day-to-day and commercial world. VQuakr (talk) 22:40, 31 July 2019 (UTC)[reply]

So it is fine for the thrust of a Mig engine, but not the F4 Phantom? A museum I visit has a comparison of the two, with thrust in pounds and kilograms. (It doesn't say kg-f.) I asked, and it seems that the Smithsonian has official museum guidelines that say pounds and newtons, but someone goofed. But they still didn't change the sign. Gah4 (talk) 00:07, 1 August 2019 (UTC)[reply]

Do you have some examples of day to day use? Not counting spring scales calibrated in kg, with accuracy low enough not to tell the difference. Time variations in g should be small enough, that a scale calibrated in place should be fine. Gah4 (talk) 00:10, 1 August 2019 (UTC)[reply]

Not quite sure what you are asking here. What improvements to the article are you proposing? Just better (ie, some) sourcing for the section? VQuakr (talk) 00:17, 1 August 2019 (UTC)[reply]

verb[edit]

What are we supposed to use instead of

"I'm weighing the sample. The sample weighs 50 mg." ?

"I'm massing the sample. The sample masses 50 mg." ?

"I'm determining the mass of the sample." "The sample mass is 50 mg." ?

Darsie42 (talk) 23:20, 27 September 2018 (UTC)[reply]

Try a dictionary. To mass has a different meaning as a verb: it is like "to gather into a mass"—see, for instance https://www.dictionary.com/browse/mass and more at https://www.onelook.com/?w=mass and if that is not sufficient, try our wp:Reference desk/Language, because it's a bit off-topic here. See wp:TPG. - DVdm (talk) 07:19, 28 September 2018 (UTC)[reply]

I need the answer to this, as it is now needed in the Mole (unit) article. There are statements like ... weighs 40.xxxx grams.', which is wrong for this reason. Gah4 (talk) 21:01, 2 February 2019 (UTC)[reply]

[Eotvos-1] "One hundred years of the Eötvös experiment". link.springer.com. Springer-Verlag. Retrieved 6 May 2017.

[Eöt-Wash-2] "Laboratory Tests of Gravitational and sub-Gravitational Physics". www.npl.washington.edu. University of Washington. Retrieved 6 May 2017.

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