Wikijunior talk:Solar System/About gravity, mass, and weight/Archive 2

Rewrite?
mass in science does not mean weight! weight is mass times acceleration due to gravity. or in formula form w=9.8m/s₂*m so to figure weight all you do is the mass of an object times 9.8m/s₂

Alexa J. an8th grader

I happened by this module and was astonished by its opening sentence:

"'This is a myth-busting section to help you avoid getting confused about what it means to talk about your mass, or the more commonly used term for this, weight, on another planet.'"

If this module is meant to be "myth-busting", it surely must not start with something that can read as confirming the very misunderstanding it is setting out to undo, viz that 'mass' and 'weight' are interchangeable terms and concepts! (see italics)

I read further and was dismayed to see that the article fell into this trap by the third paragraph of the 'What are mass and gravity?" section. Note the shift from referring to mass to referring to weight (underlined):

"'People used to think that that if you dropped a massive object (like a canon ball) from a height that it would fall to Earth more quickly than a li g hter object (such as a ball bearing)...'"

Also, as mentioned in the Leaning Tower of Pisa thread above, the Leaning Tower of Pisa story is unsubstantiated (and most likely apocryphal).

Wishing to remove these errors and clarify the material, I've tried rewriting the opening two sections. I hope I have kept them sufficiently straightforward and that people find my contribution helpful. I plan to review the remaining sections soon.

I think this Wikijunior book could be great and I look forward to sharing it with my niece in the not-too-distant future.

Best wishes, David Kernow 04:03, 18 October 2005 (UTC)


 * Did you actually read any of the authorities cited above, David Kernow? Obviously not.


 * What you need to distinguish is mass and force. Weight is an ambiguous word; it can be either mass (in its physics jargon meaning, not, for example, what a bodybuilder refers to in discussing muscle mass, and not a church service either) or certain particular kinds of force (but not forces such as the thrust of a rocket or the tension due to a spring or rubber band).


 * Of course, that isn't the only word which has more than one meaning. Kids age 8-11 may well know the word "massive", but they're likely to know it in the meanings related to occupying a large volume, or a large part of their field of view, not in the technical jargon meaning common in college physics.  You'd have a hard time convincing them at this stage that an ant, or a bacterium,  is "massive"&mdash;and most of their parents will also think you are off your rocker if you make that claim. Metric1000 09:11, 18 October 2005 (UTC)

Thank you for your prompt response.

I have read the authorities cited above. I am trying to keep in mind, however, that this module is in a science-based book meant for young people. It is an opportunity to introduce (or confirm) the distinction science makes between mass and weight, before the ambiguous or metaphorical uses of these terms in common parlance and literature instil any confusion. I have reviewed the module's opening statement and hope it satisifies your point.

I note your mention of force above and inclusion at the end of What are mass and gravity? ¶2. Force is a concept that is also prone to variable use and meaning outside science. Since I believe it is possible to write the module's opening sections without referring to it directly, I chose to do so in order to keep the content as straightforward as possible. I have simply adopted the use of "pull" that was already in place before I edited What are mass and gravity? ¶2. The same applies as regards avoiding the term "inertia" or the verb "accelerate".

I also use "move" rather than "speed up" (or "accelerate") as I can imagine a young person thinking that in order for something to speed up it must already be moving.

I agree that my use of "massive" is probably too adult; thank you for pointing this out. I also remembered that it has that rap/hip-hop slang sense of "very good" or "a gang or collective". Rest assured that I don't see myself trying to convince anyone that an ant or bacterium is "massive".

David Kernow 13:58, 18 October 2005 (UTC)

On re-reading the What are mass and gravity? section, I was unconvinced by the "There is always a balance between..." sentence. I've now amended it, but am still not wholly convinced. What's being implied is the proportionality between forces and masses, but "proportionality" is a long word and another concept...

David Kernow 14:46, 18 October 2005 (UTC)


 * You don't seem to understand that it isn't the normal usage, the usage those children are going to be most familiar with, which "instills confusion". That normal usage is quite legitimate and proper, well justified in history, in linguistics, and in the law.


 * Speaking of confusion, there wouldn't be any chance that you yourself would be so confused as to think that when my ketchup bottle has a "net weight" of "24 oz (1 lb 8 oz) 680 g", that any of those units either are or should be units of force, are you? Or that a gold bar with a "troy weight" of 402.09 oz would have a different weight in Hammerfest, Norway than it would in Quito, Ecuador? The troy ounce is a "unit of weight" isn't it, as almost any dictionary will tell you?  But there is not, and never has been a troy ounce force.  It isn't is any different, of course, if that gold bar's weight is expressed as 12.5064 kg as is stamped on the top one in the pile shown here.  Gold buyers and sellers wouldn't be silly enough to weigh their gold in newtons, or in pounds-force.


 * Because if you don't understand those basic facts, then you are the one likely to instill confusion. You can make the point that in the sciences the sciences, the word "weight" is often limited to a different meaning than what these children are most accustomed to, and that they as well as grownups often use various meanings of the word without having the distinctions clear in their own minds.  But just remember, we are fortunate that nobody ever gave any high school chemistry teacher or college physics professor any say-so as to what the word weight means when we buy and sell salt or gold or platinum or diamonds (carat weight, where one carat is exactly 1/5 gram) or anything else.  Nor in the medical sciences, when the doctor or nurse measures our body weight, and uses it to calculate our BMI.


 * Furthermore, those who use it that way own this word; they have the prior claim to it, by a long shot. They've been using this English word that way for over a thousand years, back into the "Old English" days.  It is the newer, spinoff variant that "instills confusion"; a meaning that only showed up on the scene about 275 years ago.


 * The use of the term weight is much more uniform and consistent and correct within commerce in general than it is in science in general. That Canadian standard above got it right, using "nearly always" in describing the former context, and the weaker terminology "primarily" in connection with science and technology.


 * Consider, for example, that agricultural scientists in the U.S. and Canada (yes, today) often use "bushels by weight" in publishing the yields of different varieties on their test plots, and measure the quality of various grains and legumes and oilseeds using a "1,000 kernel weight" in grams. Biologists and paleontologists measure the body weight of animals in the same way that medical doctors do, using the same units (in metric units, they use the proper SI units:  always grams or kilograms (occasionally metric tons), never kilonewtons and the like).


 * {| border="1" cellspacing = "0" cellpadding = "2"

! bgcolor="#F08080" | Google ! bgcolor="#F08080" | hits
 * + Weight often means the same as mass in science and technology, too!
 * molecular weight
 * align="right"| 7,370,000
 * "molecular weight" site:nist.gov
 * align="right"| 773
 * "molecular weight" site:harvard.edu
 * align="right"| 25,800
 * "molecular weight" site:.edu
 * align="right"| 530,000
 * "molecular weight" site:.gov
 * align="right"| 1,490,000
 * "molecular weight" site:.uk
 * align="right"| 217,000
 * "1,000 kernel weight"
 * align="right"| 11,300
 * "nest weight"
 * align="right"| 791
 * "liftoff weight"
 * align="right"| 9,340
 * reptile "body weight"
 * align="right"| 43,400
 * BMI "weight in kilograms"
 * align="right"| 106,000
 * }
 * align="right"| 791
 * "liftoff weight"
 * align="right"| 9,340
 * reptile "body weight"
 * align="right"| 43,400
 * BMI "weight in kilograms"
 * align="right"| 106,000
 * }
 * BMI "weight in kilograms"
 * align="right"| 106,000
 * }
 * }


 * I'll leave it to you to check out things like "atomic weight", "formula weight", "gram-equivalent weight", and the like. And abbbreviations such as "at. wt.", common on many of the zillions of Periodic Tables of the Elements found on the internet, many on the sites of colleges and universities around the world.


 * It isn't your car mechanic, or your hairdresser, or a long-haul truck driver, or the butcher, the baker, or the candlestick maker, who are going to use terms such as "molecular weight" and "atomic weight" in connection with their work. They are only used in connection with the sciences such as chemistry and physics.


 * NASA, of course, tells us that the "weight" of the Apollo 11 lunar module, at liftoff of its ascent stage, was 10,776.6 pounds. (See NASA's Selected Mission Weights page; other sources will tell you that this liftoff was accomplished with a thrust of about 3,500 pounds-force, which may help you understand the meaning NASA uses here.) You can find lots of other use of weight with the same meaning as mass has in physics jargon among rocket scientists and engineers.


 * On to other things: It takes no force to "move" something, or more precisely, to keep it moving. That is an all-too-common misconception; we don't need to reinforce that incorrect idea in the minds of these children. The force is needed only to accelerate it, or to overcome some other force that is accelerating it in a different direction from the direction in which it is moving, such as friction (but we are ignoring air resistance in the examples, so that doesn't apply).


 * Force isn't the word you need to avoid; much better to avoid the ambiguous word "weight". Of the various meanings of force, there is usually only one of them which we measure and assign a numerical value; there isn't any real difficulty in either using that word or making it clear what we mean by it.  Metric1000 21:29, 18 October 2005 (UTC)

Thank you for your latest thoughts.

I appreciate your concern that a (young) reader is likely to have had the notions of mass and weight conflated through everyday use and so may be unsettled to read that, as regards science, they are distinct attributes. In view of this I have therefore amended the opening paragraph.

No, I don't think the weight of a ketchup bottle or the other objects you mention need be described in units of force, as usually they exist in the same relatively strong (and near-uniform) gravitational field. If they are taken from the Earth to another body in the universe, however, they may once again exist in a relatively strong gravitational field, but it won't be the same strength as that of the Earth. Hence their weight - which still need not be measured in units of force - will not be the same as before. This module is in a book about our solar system, about bodies with gravitational fields whose strengths differ from that of the Earth, so surely the distinction between mass and weight is pertinent?

I agree that my phrasing "takes more/less effort to move" in What are mass and gravity? ¶4 might be read as implying that, friction aside, force is constantly required to keep something moving. Thank you for pointing this out. I hope my amendments suffice.

David Kernow 02:44, 19 October 2005 (UTC)


 * Conflated? That isn't exactly the proper description of what happens.
 * There are indeed two "distinct attributes" involved here.
 * But a "difference" between weight and mass isn't something that just exists. It needs to be created; there is no God-given meaning assigned to our words.
 * The questions here are matters of history and of the law. The science involved here is semantics, a branch of the science of linguistics, not astronomy (and also not chemistry, not physics).
 * That "difference" can, of course, be created, within the limited jargon usage of a particular book, even a particular classroom, and to a lesser extent within some broader field of activity. That doesn't mean that the difference exists outside that context, however.
 * Beyond that, what is it that you don't understand about millions of uses in science of the word weight with the very same meaning that mass usually has in physics jargon?  Is it just that you don't know what "molecular weight" means, that you don't know what the weight in grams of 1,000 kernels of wheat means, you don't know what an "egg weight" of 65 g (Welsumer) means, etc.?  You didn't address that point at all. Metric1000 14:56, 19 October 2005 (UTC)

Hello again.

I too believe "there is no God-given meaning assigned to [] words". I appreciate that people come to use the words 'mass' and 'weight' interchangeably because almost all of us spend almost all our lives in the same, effectively constant circumstance: Earth's gravitational field. But the distinction between mass and weight becomes pertinent as soon as this circumstance can no longer be assumed - when, for example, other planets in our solar system are considered, as they are in this book.

I hope this clarifies how I addressed your point in my previous message ("No, I don't think the weight of a ketchup bottle or the other objects you mention need be described in units of force, as usually they exist in the same relatively strong (and near-uniform) gravitational field.").

David Kernow 23:44, 19 October 2005 (UTC)


 * BTW, thanks for making it abundantly clear that there are cases in which confusion has already been instilled in some people, with your confused ramblings about the ketchup bottle. The strength of the gravitational field is totally irrelevant; 1 lb 8 oz of ketchup on Earth is still 1 lb 8 oz of ketchup on Mars, and 680 g of ketchup on Earth is still 680 g of ketchup on Mars.  That's just as it should be.  If that weight "still need not be measured in units of force" (as you said above), just how in the world are you imagining that that weight "will not be the same as before"?   In fact, it is actually stronger than "need not"; it is "ought not".  It certainly wouldn't be pertinent to claim that the net weight of that bottle of ketchup would change, would it?  Metric1000 16:19, 19 October 2005 (UTC)

The mass of the ketchup would remain the same, but its weight would change. I believe this is meant to be the point of the module.

If I recall correctly, Mars' gravitational field is around a third that of the Earth, so a weight of 1 lb 8 oz of ketchup on Earth would become 8 oz on Mars and a weight of 680 g would become about 227 g.

What someone measures with scales is weight, even if (thanks to their Earth-bound circumstance) they also then equate that measurement with mass. One way to measure the mass of an object regardless of gravity is to multiply the object's volume by its density.

David Kernow 23:44, 19 October 2005 (UTC)


 * You can certainly choose not to call this quantity of ketchup weight, if you so desire. But that is your only option.
 * Note also that your making this choice will not affect the meaning of the word weight when someone else uses it in this context. Nor will your making this choice give you any standing that they are making some kind of error in doing so.
 * It is not a legitimate alternative for you to continue to call the quantity we measure in the sale of ketchup or gold or anything else by the name weight, but to misapply a definition of this ambiguous word which is incorrect in that context.


 * Most 10 years olds should already know enough to have great difficulty with your claim that 680 g on the Earth would be 227 g on Mars. It is a little different with pounds--those Fred Flintstone units are like obsolete software, no longer fully supported and updated.  Like that old software, they will probably continue to work for your own use for some time, but if you eventually want to communicate with the rest of the world, they might fall short.  With the metric units, the keepers of our standards have been telling us for 45 years to stop using kilograms-force, and they are finally disappearing.  However, nobody is ever going to bother to tell us to stop using pounds-force without telling us to use pounds of any kind.  That doesn't really matter much to this discussion, however; we do not and never have used pounds-force in the sale of goods by weight.


 * You also seem to have no understanding whatsoever of how balances work, and you appear totally clueless about the way in which the scales used in commerce are tested and certified for that use. See, e.g., weighing scale.
 * There isn't a snowball's chance in hell that if you are accused of giving short weight, some government weights and measures official would mistakenly measure force instead of mass in determining whether legal charges should be brought against you.
 * Note also that while the law does define a pound as 0.45359237 kg exactly (see U.S. version above), it does not define a pound force. Now ask yourself, "Why in the world does the law bother to define a pound in the first place?"  It is, of course, for the protectionof consumers, as a tool to help keep merchants honest.   The law quite properly defines the units we can legally use for that purpose (grams and kilograms and pounds and ounces in the United States, for example). Metric1000 16:48, 20 October 2005 (UTC)


 * I think our discussion hinges on what you, I and scientists make of the following scenario.


 * We are on Earth and have an object, say a bottle of ketchup. We place it on one side of a balance - a comparator - and then see how many identical blocks need to be placed on the other side of the comparator to achieve equilibrium. Let's say it's five.


 * We then take a spring and measure its length whilst unstretched; let's say it's nine units. We hang the bottle of ketchup from it and find the length of the spring is now (say) twelve units.


 * We travel to Mars with the bottle of ketchup, the comparator, the blocks and the spring. On Mars we place the bottle of ketchup on one side of the comparator and find that the number of blocks needed on the other side to achieve an equilibrium is...? I - and I believe you and the scientists - would say five.


 * We take the spring and - I hope you agree - find its length whilst unstretched is still nine units. We hang the bottle of ketchup from it and find the length of the spring is now...? Because Mars' gravitational field is about a third that of the Earth, I - and I believe scientists - would say ten units, not twelve. What do you say?


 * The comparator is measuring (more accurately, comparing) mass, whereas the spring is measuring weight. The mass remains constant between the Earth and Mars (and elsewhere). The weight changes. I believe this is significant in a book about celestial bodies, especially one to be read by young people.


 * David Kernow 23:36, 20 October 2005 (UTC)


 * The real question is, which of those measurements likely to meet the requirements of the law when it comes to selling ketchup (or gold or whatever) by weight. We only need to look at what is actually done for measurements on the Earth today; there are significant variations in the strength of the gravitational field on Earth.  Even if you limit yourself to sea level on Earth, the variation is 0.53%, more than one part in 190, and there are variations with elevation wrt to sea level as well as with latitude.  It would certainly make a difference if force were measured rather than mass if you were buying or selling a 400 oz t bar of platinum, wouldn't it?  Or those 12½ kg gold bars I mentioned earlier, measured to the nearest 100 milligrams?  Your homework:  If that top gold bar weighs 12.5064 kg, how much force would it exert due to gravity at Hammerfest, Norway?  How much force would it exert due to gravity at Quito, Ecuador?  Any units of force you like, to however many significant digits (can't be more than six) you can get.


 * In fact, many spring scales have "NOT LEGAL FOR TRADE" or words of similar import right on their face. A few spring scales are legal for trade, but they must be tested and certified before they can legally be used.  The same applies, of course, to any other kind of scale, including piezoelectric load cell devices or whatever.  Some of you probably remember those old Toledo Scale Company scales, with the motto "HONEST WEIGHT:  NO SPRINGS" boldly presented to the customer.


 * Do you have any idea whatsoever how that testing is done?
 * Rather than your "blocks", a government inspector will come in with a few standard weights and test the scale in operation, in the very location in which it is used. Maybe, for example, a 200 g weight and a 100 g weight, and they will see what the scale reads with one or the other or both of them, placed at varying locations on the weighing pan, see if it makes any difference if weights are being added or being taken away, things like that.
 * But what, exactly, is it that is known about those reference weights? It isn't the amount of force that these weights exist.  They don't custom-make new weights which have a different mass, so that they can tell precisely how much force these weights exert at each particular location, and thus are useless outside that location.
 * Moreover, they wouldn't want to do that, even if they had some easy way of doing so. We are interested in how much stuff we have, and we don't really care much about how hard it will press down on the table.


 * You would, of course, also have to separate the weighing of the empty bottle, and the bottle including its contents, since we are interested in the net weight when we buy and sell goods by weight.


 * Now, let's check your understanding of history. Let's suppose that somebody added a new word weyghte or (whatever spelling might have been used at the time, there was very little standardization in spelling then and what did exist was often slightly different from what we use now) to the English language some time over 1,000 years ago, using it to mean the quantity that they measured with one of those comparators you talked about.  So what, exactly, did this new word weyghte mean at the time, using everything we know now?


 * To put it another way, people have been weighing things for 7,00–8,000 years or so, since long before the word weight entered the English language (that is, of course, the word we use today to refer to measurements made before the English word existed). But nobody used any weighing devices that were not those mass-measuring balances, outside the past 200 years.


 * When the metric system was invented, nobody used weighing scales that were not mass-measuring balances.


 * Sir Isaac Newton never used weighing scales that were not mass-measuring balances. Probably in part because of his day job as Master of the Mint, he liked to weigh things in troy ounces and troy grains (he often used French toises and pieds for length, however).  Of course, there is one way in which the troy units differ from their avoirdupois cousins, and differ from grams and kilograms as well&mdash;there is not today and never was a troy ounce force.


 * Note that those comparators, the mass-measuring type of scale we normally call a balance, were the only scales that existed at the time. They couldn't have used anything else.  Spring scales didn't even show up in the picture until the Nineteenth Century, and the various types of load cell devices are even newer than that.


 * Of course, thanks to the work of some 17th century pioneers, we are now able to distinguish between the mass of an object as that term is used in physics jargon, and the force that it exerts due to gravity. But after we humans got to be so all-fired smart three centuries ago, what exactly did we change about the quantity we measure when we buy and sell goods by weight?    Answer:  absolutely nothing. That is the most relevant point to be made here.  What exactly did we change about what we call this quantity?  Answer:  Nothing.  We still call it weight, even if a few people are misguided enough to think that calling it mass instead is a sign of their intellectual superiority, and many more are even more misguided and have deluded themselves into believing that since it is in fact called weight, it cannot possibly be the same thing as mass. Metric1000 15:26, 21 October 2005 (UTC)

Yes, as in an earlier reply, I acknowledge that people now, in history, in everyday life, in law, in literature and so on have and continue to use the words 'mass' and 'weight' without distinction. Since the seventeenth century, however, science has come to use these words to refer to distinct attributes. 'Mass' and 'weight' might have continued as synonyms in science - probably for weight, following the realisation that we're all living, measuring, buying, selling, writing and legislating in the same gravitational field - and a third word adopted, derived or invented to refer to amounts of matter, but this isn't what has happened. Science has come to use 'mass' to refer to amounts of matter and 'weight' to refer to the effect amounts of matter have in gravitational fields. That this has happened might not matter as regards all our everyday Earth-bound activities, but it does when thinking and writing about other celestial bodies, notions such as orbits and so on. Furthermore, drawing some attention to a distinction such as that science makes between mass and weight is a great opportunity to remind young people that new awareness can result from considering something otherwise taken as innocuous or for granted.

David Kernow 01:43, 22 October 2005 (UTC)


 * Of course we use them without distinction, in contexts where no distinction can be made.


 * Why do you keep repeating things like "might have continued as synonyms in science"? Just what, exactly, is it that you cannot understand about nearly seven and a half million Google hits for "molecular weight"?  That's not even considering atomic weight and at. wt. and formula weight and the like.  Let's deal with that before we go any further, okay?


 * Where did you get the idea that the medical sciences are somehow excluded from science?


 * Sure, "it does [matter] thinking and writing about other celestial bodies." But just where in the world do you imagine that Lunar Module was, when NASA tells us that its weight at liftoff of its ascent stage was "10,776.6 lbs"?  Metric1000 00:31, 23 October 2005 (UTC)

I have posted the following request for comment as I think the time has been ripe for a while now for comments, suggestions and advice from other people as regards this module.

David Kernow 02:01, 23 October 2005 (UTC)


 * If you expect anyone else to understand you point, they, like me, might be interested in your answers to the questions in the three paragraphs immediately above. Why are you unwilling to discuss them?  Have you already answered them in your own mind, and just aren't willing to admit that you are flat-out wrong?  Metric1000 03:57, 23 October 2005 (UTC)

I'm going to agree with David here. There is a definite difference between weight and mass, and it needs to be made clear in a scientific book with an aim of instructing children. Mass is the amount of matter in an object. Weight is the force due to gravity being exerted on an object. Grams is a unit of mass. Newtons is a unit of force. There is no scientific confusion in those terms.

For an experiment, take a bathroom scale and climb a mountain. You will weigh less at the top than at the bottom. This is because a bathroom scale does not measure mass- it measures weight. Think of how it works- it works by you depressing a spring due to the force of you standing on it. Its working by measuring the force, not the mass.

So, how do we have pounds and ounces defined in terms of grams? Such as the ketchup bottle or troy ounce you mentioned? Simple- weights are always reported in terms of weight at sea level. When you assume a certain distance from a center of known mass, you can convert from mass to a weight by multiplying by g at that distance, then multiplying by the conversion factor.

Also, despite however many google hits you found, the correct term is not "atomic weight". It is "atomic mass". The reason for the term confusion is the same as the reason in other spheres- antiquated usage from pre-physics days when we didn't know there was a difference. If you search for atomic mass, you will find almost 15 millio google hits- almost 3 times atomic weight.

I'm sorry Metric100, but your argument is wrong. (By the way, does the name strike anyone else with irony)? --Gabe Sechan 02:28, 23 October 2005 (UTC)


 * Yes, you are right. Grams are units of mass, newtons are units of force.  When "weight" is measured in grams, it is a measurement of mass.  On those rare occcasions when "weight" is measured in newtons, it is a measurement of force.  That's what this module has tried to make clear. (Of course, there are also grams-force, units that have been deprecated since the International System of Units was introduced in 1960.  We still see far too many vestiges of their use, but almost never for anything that is called "weight".  Rather, they are still used for things such as the thrust of jet and rocket engines, for tension of bicycle spokes, for pressure gauges in kg/cm², and things like that.)


 * You have a totally confused notion of the definition of pounds and ounces. Some sources have been cited above; I'll cite some more just after this reply.  Just look at that official definition in United States law, for example, the Federal Register Notice of July 1, 1959.  Show me where it says anything about gravity, or kilograms-force, or anything along those lines.  There's absolutely nothing like that in the definition.


 * We often use spring scales in our bathrooms, because they are cheap and they do a reasonable job of recording differences over time, as long as we always use the same one. But if you want to know what we are measuring, you need to look at what we measure when we get serious about our weight, and go to the doctor's office or the gym.


 * Of course, your claim that pounds and ounces are defined "in terms of weight at sea level" is patently absurd. What, exactly, is this "weight at sea level" in your estimation?  Note that the normal acceleration of gravity at the poles is 32.25780 ft/s², but normal gravity at the equator is only 32.08766 ft/s² (and local anomalies will make the total difference at sea level slightly more than that).  So, what would you say the "weight" is of that 12.5064 g gold bar, in the Wikipedia image linked to above?  How many pounds would that be, at sea level at the North Pole?  How many pounds would that be, at sea level at the equator?


 * All those "molecular weight" hits are "antiquated usage from pre-physics days"? Get real.  You can start by explaining why 25,800 of those hits were at the Harvard University site, and 773 of them at the site of the National Institute for Standards and Technology (NIST), the keepers of our standards in the United States.


 * You get more hits for "atomic mass" for two simple reasons. First, you didn't do an exact phrase search. To do that you need to put quotation marks around them, or use the advanced search input. Doing that, I get 561,000 for "atomic weight" and 654,000 for "atomic mass".  Second, there is a unit of mass called the "atomic mass unit", or the modern preferred name "unified atomic mass unit" with the symbol "u" rahter than the obsolete "amu".  Searching for site that include "atomic mass" but do not include "atomic mass unit" or "atomic mass units", I get only 512,000 hits.  The same point can be made by looking at molecular weight, because we don't have a "molecular weight unit".  Searching for the exact phrase "molecular weight" today, I get 8,400,000 hits, but searching for "molecular mass" I get only 1,780,000 hits.

No irony at all; I'm smart enough to know what a pound is, and how it differs from a pound-force, and what a kilogram-force is as well, and the difference between an ounce of platinum and an ounce of palladium, the difference between a Canadian ounce of Coca-Cola and a U.S. ounce of Coca-Cola, and the difference between a U.S. ounce of evaporated milk and a U.S. ounce of sweetened condensed milk, and the difference between a U.S. pint of blueberries and a U.S. pint of blueberry ice cream. Can you come up with any better reasons to strongly prefer the modern post-1960 metric system. Metric1000 14:13, 23 October 2005 (UTC)

Use of Kilograms as a unit of "weight"
In this instance, I think it is very misleading to use the term "kilogram" for weight measurements. Where we are at an impasse over is trying to find a way to describe the effects of gravity upon us when we are in a substantially different gravitational field, like standing on the Moon or Mars.

The most appropriate SI unit for describing the difference is the newton (OK, you've won that point Metric1000), because clearly a 100 kg person standing on a spring scale on the Earth will push down with 1000 newtons, while on the Moon it would only be 170 newtons. The problem here is that your mass would still be 100 kg, and to this point Metric1000 is technically correct, but misses the point that the effect of gravity would be quite a bit different.

It is also correct that even space medicine discussions still use the term "weight" for astronauts while in orbit, even though they are in a micro-g environment (the ISS does have its own gravitational field, BTW, affecting some experiments done there). The truth is, however, those discussions are done to relate to Earth-bound measurements and to keep consistant health concepts, not to describe the effects of a change of gravitational field.

The whole point of this section is to try and convey the fact that there are differences between the properties of mass, which doesn't change from one gravitational field to another, and to describe the effect of applying force while in that environment which does change. You can still be crushed to death by a 1000 kg object traveling at 40 km/hr if you are between that object and a wall on the Moon. Gravity will not make one bit of difference. On the other hand, playing a game of soccer (to choose a more international sport) is going to be played quite a bit different on the Moon than on the Earth. Hitting a golf ball on the Moon (it happened during the Apollo XV mission) is going to have that ball travel much further than on the Earth for several reasons, even with problems of trying to hit the ball while in a spacesuit.

Where this section needs to be rewritten is to come to a compromise between ignoring the fact that mass is the same everywhere and that gravitational fields do change. Rather than trying to suggest that if you "weigh" 100 kg (using this as an example here) on the Earth you would "weigh" 17 kg on the Moon, it would be better to describe that if you can jump up 40 cm here on the Earth that you would be able to jump up much higher on the Moon. Or if you can "lift" 100 kg on the Earth that you would be able to "lift" 600 kg on the Moon.

In short, rather than trying to digress into "weight" vs. "mass", lets describe the effects of the change of gravity. What is the same, and what is different? If you were in a Jovian gravitational field, how different would things be with gravity going the other way? Would your bones break just trying to jump at all? How about on Phobos, where you could accidentally jump "off" the moon entirely if you jumped up too long, and that even a gentle pushup might take a couple of hours to come back to the ground after going more than 1 km high from that gentle push.

We can do a better job than the typical science textbook on this subject, and for that I do appreciate what Metric1000 is trying to accomplish by raising that bar. On the other hand, we need to also acknowledge that there are distinctively different effects for many human activities when the gravitational environment is changed. How do we describe that very different environment? --Rob Horning 11:07, 23 October 2005 (UTC)


 * It is much more misleading to bury your head in the sand and pretend that kilograms and pounds (units of mass) are not used to measure "weight".
 * We have ample evidence on this talk page showing that many of the editors here do not understand what that means. Let's not raise another generation of kids with the same misconceptions.
 * It is absolutely essential that we explain that the weight these students are most familiar with—weight as we use it for buying and selling goods by weight, and for measuring human body weight for the purposes of health and fitness (the reasons we normally weigh ourselves)—is the same thing that some scientists like to call mass.
 * Otherwise, you are pretty much saying what I've been saying all along. I guess I'll have to put together a list of all the silly statements that were originally placed in these modules, before I fixed them up a little bit. Claims that kilograms would change, etc.
 * For that golf ball, you'll get essentially the same speed off the club as you would swinging in a spacesuit on Earth; it just takes gravity longer to pull it back to the surface. Of course, remember that in jumping, it is the change in the height of the center of gravity that matters most, and high jumpers and pole vaulters do not clear the bar in an upright position.  Metric1000 13:37, 23 October 2005 (UTC)


 * There are other effect that can be taken into consideration with the golf ball as well... Lack of atmospheric drag, and an increased curvature of the surface will also have a significant impact (the golf ball is on a sub-orbital ballistic trajectory, after all). Still, I'm going to ignore those extra factors for this article.  I'm going to introduce a new "section" into this article going over precisely the concepts I've discussed, to explain what is different and what is the same in different gravitational fields.  Send arrows my way if you don't like what I've put in.  --Rob Horning 05:03, 24 October 2005 (UTC)


 * The "formula" that I used to determine height was trying to approximate how high a typical kid can jump up, and then go backward to try and find what the "takeoff velocity" was to reach that height. Going backward, I found the time it took to get that high and doubled it to determine how long the kid is in the air.  Using basic equations of the laws of motion and assuming a consistant "take off" velocity I got the amount of time you would spend before accelleration due to gravity would bring that velocity to zero.  Plugging that time into the time-distance motion formula (1/2at^2+vt+s) in turn gave me the height a kid would reach if they were jumping up.  On the whole, I think this is a better way to approach the subject.  And these are things that kids can relate to as well...perhaps better than "how much I weigh on X".  I'd like to do some calculations on a kid kicking a ball, but I need to determine the vertical component to do the calculations.  Any thoughts? --Rob Horning 07:19, 24 October 2005 (UTC)


 * The curvature is totally irrelevant on the scale of a golf ball's travel.
 * Other factors come into play in lifting things, too, of course. For example, whenever you lift something, you are also lifting at least part of your own body at the same time.  Metric1000 12:23, 24 October 2005 (UTC)


 * While I would agree you are also "lifting" your arm, but as I pointed out that only on the Earth itself is this a significant factor anyway. I'm just trying to present some "hard numbers" that kids can compare their experiences to that do show a difference in gravity has different experiences.  I would also like to try and find some experiences that would demonstrate where pushing mass is the same regardless of what planet or moon you happened to be standing on.  Getting hit by a bullet from a gun and getting crushed by a car against a wall seem a little too gruesome for a kids book, even though it is an accurate depiction.  I would be very careful about pushing large mass objects around on Phobos, because kenetic energy of an object will be identical everywhere.  You just don't have the large acceleration due to gravity like you find on the Earth.  --Rob Horning 14:58, 24 October 2005 (UTC)


 * Pushing a canoe away from a dock is good. Wouldn't work quite the same in the Sea of Tranquility, however.  Metric1000 18:58, 24 October 2005 (UTC)

Sources--pounds are units of mass
Pounds are by definition units of mass exactly equal to 0.453 592 37 kilogram. Sources: 
 * United States law: Federal Register Notice of July 1, 1959, F.R. Doc. 59-5442; Filed, June 30, 1959; 8:45 a.m. pdf file pdf file (same pdf file, two URL)
 * U.K. law: Weights and Measures Act of 1963 (still primary)
 * Statutory Instrument 1995 No. 1804


 * Canada law: Weights and Measures Act of 1953 (note that Canada had already adopted these definitions of both the yard and the pound six years before the same values were adopted by international agreement)
 * Australia law:
 * National Measurement Regulations 1999, Statutory Rules 1999 No. 110 as amended made under the National Measurement Act 1960 pdf file
 * 1979 No. 65 Weights and Measures (National Standards) Regulations (Amendment) - Reg 5


 * Ireland law:
 * Statutory Instrument No. 91/1976, Weights and Measures (Metric Equivalents) Order, 1976
 * Metrology Act, 1996,


 * South Africa law:
 * New Zealand law:
 * Metric1000 14:15, 23 October 2005 (UTC)


 * pound and pound-force
 * Lewis V. Judson, Weights and Measures Standards of the United States: a brief history, National Bureau of Standards Special Publication 447, originally issued October 1963, updated March 1976. pdf file as graphic images (not searchable), 46 pages; Library of Congress online catalog. Includes the Mendenhall Order of 1893 first defining pound as fraction of a kilogram in the United States, and 1894 clarification, much more.
 * Metric1000 14:49, 23 October 2005 (UTC)
 * Metric1000 14:49, 23 October 2005 (UTC)


 * Barry N. Taylor, Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 1995. html version, pdf version, order a free printed copy.  This contains an extensive list of conversion factors from non-SI units in Appendix B.  It always distinguishes between pounds (units of mass, symbol lb) and pounds-force (units of force, symbol lbf).  See particularly the footnotes (on a linked separate page in html) for pound and for pound-force.
 * Metric1000 18:44, 24 October 2005 (UTC)

Responses to request for comment
There is only one pound, but it has two definitions. I oppose the idea that references to pound as mass, or pound as weight, must be corrected. See User:Kernigh/pound for details. --Kernigh 03:28, 24 October 2005 (UTC)


 * Actually, there are still three pounds in use as units of mass, and one and only one pound-force. Pounds-force are uniquely identified by that name.  They are such a recent spinoff that of all the hundreds of different pounds used at various times and places throughout history, only one of them has spawned a unit of force of the same name that has seen anysignificant use.


 * As far as your user page goes, you do understand that slugs are a 20th century invention, first used early in that century but not appearing in physics books until about 1940, don't you? And completely gone from almost all physics books now, except maybe in a table of conversion factors?


 * When the U.S. first defined the pound as 0.4535924277 kg exactly, slugs did not exist.


 * Do you know what a poundal is? Tell us.  Note also that poundals did exist in 1893/1894, and the metrologists doing the redefining of the pound would have been aware of their use.  Metric1000 10:45, 24 October 2005 (UTC)


 * I Dont really see any reason for all the confusion. Why would you write something that--while it might be factually correct in some limited sense--only serves to increase confusion? Why would we list pounds as being mass, or kilograms as being weight, when it would be much easier (and would lower alot of blood pressure here) if we just kept things in terms that most people understand? kilogram = mass, pounds = weight, weight != mass. A few simple distinctions, and nobody gets confused, and everybody is happy. --Whiteknight T C E 11:33, 24 October 2005 (UTC)


 * Get real. My ketchup bottle, and that of the American kids this is apparently aimed at now, says it has a "net weight" of "24 oz (1 lb 8 oz) 680 g".  Both English and metric units, that's standard.  That's "weight", whether it is pounds or pounds and ounces or grams.  Those are units of mass, not units of force, whether they are pounds or ounces or grams.  No manufacturer ever makes two different measurements to put on the label, and no manufacturer ever varies the relationship between those two numbers based on the local gravity at the place where this product will be sold (and variations on Earth certainly are great enough to that it would vary at the gram level if these were grams force).


 * Even in the United States, many hospitals measure the "weight" of their patients in kilograms, and those are the proper units for this used throughout the world. When pounds are used in the United States, this "weight" is not measured by a different method than when it is measured in kilograms, and it is not measured using units that are not units of mass just as the kilograms used throughout the world are units of mass.
 * There are already a zillion sources cited here for those facts. Did you forget to ask yourself the obvious question, "Why in the world does the law bother to define a pound in the first place?"


 * Those kids, and even our Whiteknight in shining armor, have not only seen that "net weight" on packages, but have also heard of other things like "carat weight" and "bantamweight" and maybe even a unit of mass (never of force) called a "hundredweight"; a few probably even know what "atomic weight" means.


 * After all the discussion here, can't you figure out that the two things you need to distinguish are "mass" and "force"? Metric1000 12:11, 24 October 2005 (UTC)


 * Mass ignorance is not correctness, no matter how many ketchup bottles the equivalency is listed on. On earth, gravity is basically a constant, with a value that can be reasonably rounded off and used in general. When your ketchup bottle shows that the product weighs a certain amount (be it in pounds or ounces), the eqivalent mass in SI can be calculated out in grams. Too few people are familiar with Newtons to make a direct weight -> weight conversion. The fact that gravity is nearly equivalent in all places where a person could make a perminent residence in which to store and consume their ketchup, does not change the fact that the conversion formula is pretty standardized. Also, keep in mind that the people marketing the ketchup are rarely scientists or engineers, but are instead artists and business majors who may not all be well-versed in the specifics of unit conversions. --Whiteknight T C E 18:15, 24 October 2005 (UTC)


 * You are absolutely right about mass ignorance not being correctness. It isn't, of course, a matter of "the conversion formula is pretty standardized".  There's no "pretty" about it.  Rather, it is in fact exact.  Pounds are, by definition, units of mass exactly equal to 0.45359237 kg, since that international agreement of 46 years ago.  Sources are cited above under.


 * It wasn't, of course, "artists" and "business majors" who did the redefining, though there's a pretty good chance they could do better than Whiteknight would.  I'm absolutely buffaloed figure out why anybody would think that it would be a good idea to measure a quantity that varies with the strength of the local gravitational field, when we are buying and selling goods by weight.


 * The defining was instead done by the experts in the field, the professional metrologists of the national standards laboratories of six of the major industrial nations of the world.


 * Of course it also is not a matter of "Too few people are familiar with Newtons to make a direct weight -> weight conversion." That is quite ludicrous on two grounds.  First of all, there is no place in the whole world where newtons are legal units for the sale of goods.  Second, there is no place in the world where the sale of goods in pounds-force is legal; you are not starting out with pounds-force in the first place.


 * BTW, anybody who capitalizes "Newtons" cannot be all that familiar with them and with the rules for their use.


 * It works the same way when the rocket scientists and engineers at NASA tell us the weight of a satellite in kilograms, or in pounds which they also still use far too often. Metric1000 18:35, 24 October 2005 (UTC)


 * You sure do resort to alot of ad hominem attacks when trying to make your point. It doesnt matter if i miscapitalize "Newtons" or not, that doesnt in any way show how familiar i am with them and their use. All I am trying to say here is that we have an opportunity to alleviate alot of misunderstanding. There is no need to have pounds as a measure of mass when the SAE unit "slug" is the accepted unit of mass. Children are most frequently taught in school the differences between "weight" and "mass" and it seems like a waste of our time, and the time of our readers to nit-pick between different acceptable terms for this or that measurement. Why would we use one word ("pounds") as both a measurement for force and mass? Keep in mind, this is a book for children, and a good childrens book should alleviate misunderstandings. Also, try to keep the discussion more civil, and avoid personal attacks in the future. --Whiteknight T C E 19:35, 24 October 2005 (UTC)


 * Rather a case of the pot calling the kettle black, isn't it?
 * Before you get too carried away on this "SAE" kick, you might want to go look at the citation from the SAE Standard which David Kernow moved to the archives.


 * Study up on your history a little bit, too, and the differences between an absolute foot-pound-second system of units, a gravitational foot-pound-second system of units, an engineering foot-pound-second system of units, a gravitational inch-pound-second system of units, and how these special subsystems (each containing only a limited subset of units) are used in calculations because they all form subsystems which are "coherent" or nearly so.


 * Yes, things would be simpler if nobody had ever spun off the pound-force from the pound.
 * But we, in our little book, cannot change the fact that pounds are used as both units of mass and units of force. Since they are more commonly, by far, used as units of mass, it would be nice if we could throw out pounds-force as the keepers of our standards have done (with good, though not complete success) with the kilogram-force, which has been deprecated since the introduction of the International System of Units.  However, the English units are like old software, no longer supported and updated.  Nobody cares enough so that we would ever be told to stop using pounds-force, without being told to stop using pounds of any sort whatsoever.


 * If you are really curious about units of measure, there is another system of units reinvented several times by those insistent upon showing that those using metric units can be every bit as silly as those using English units. Try to see what you can find out about a unit of mass known by various names in different incarnations of this system:  the hyl, the TME (from a German acronym), the mug, or the term from which the latter was shortened, "metric slug".  Can you figure out what the base unit of force is in this system?


 * Just as the existence of the hyl does not and cannot prove that kilograms are not units of mass, the existence of the slug does not and cannot prove that pounds are not units of mass. Metric1000 21:15, 24 October 2005 (UTC)


 * Since you find the Society of Automotive Engineers credible, here is some more from SAE TSB003, Rules for SAE use of SI (Metric) Units, May 1999: pdf file


 * 3.11 Units for Mass, Weight, and Force— Mass units, such as kilogram, pound, and ounce, have often been used for units of both mass and force. This has led to serious confusion. In SI this confusion is eliminated because the unit of mass is the kilogram, and the unit of force is the newton. The kilogram-force (from which the suffix "force" in practice has often been erroneously dropped) is not used. Derived units that include force are formed using the newton.
 * See, even the SAE correctly characterizes them as "mass units", also "used for" force. Metric1000 21:27, 24 October 2005 (UTC)

Yes, I forgot about w:Troy pounds and w:British pounds in my previous comment. I believed that those were not relevant to the module. --Kernigh 20:41, 24 October 2005 (UTC)


 * I was referring to troy pounds (which, unlike their avoirdupois cousins, and unlike grams and kilograms as well, are never units of force, and metric pounds still in informal use in much of the world, stemming from 19th century redefinitions of various local pounds. They are 500 g exactly, and naturally those are units of mass as well.  Note also that from the time of Henry VII until at least after 1850, there were no independent primary standards for an avoirdupois pound.  Rather, they were defined as an exact fraction of a different unit of mass, just as they are today, only in that case the other unit of mass was the troy pound and today it is the kilogram.  THere were then, and are now, various secondary standards representing the avoirdupois pound, of course.  Metric1000 20:55, 24 October 2005 (UTC)