
Officially the pound is the name for at least three different physical units of mass: * The pound (avoirdupois). * The troy pound. * The metric pound, no longer officially sanctioned but still in informal use in some places. Standards bodies define the pound as a unit of mass, which are the pounds most people in everyday usage use as a ''unit of weight''. ==Origins== The Latin word ''libra'' describes a Roman unit of weight similar to a pound, and the abbreviation "lb" for the unit of weight and the signs £ and ₤ (crossed-out L's) for the currency derived from this. The word "pound" itself comes from the Latin ''pendere'', to weigh, while ''libra'' meant "weighing scale". == Measurement systems == In the Imperial units (often referred to as the pound-inch system, or ''the English system'' in the United States) there are two basic pounds defined, and also an obsolete definition of one variant of the pound. === Pound (avoirdupois) or international pound === ''Main article: avoirdupois'' The avoirdupois pound was invented by London merchants in 1303. The pound (avoirdupois) or international pound, abbreviation "lb" or sometimes number sign in the United States, is the mass unit defined as exactly 0.45359237 kilograms (or 453.59237 grams). This definition has been in effect since a 1959 agreement among the national standards laboratories of the United States, Canada, the United Kingdom, South Africa, Australia, and New Zealand. [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf] It is part of the avoirdupois system of mass units. In the United States, the pound has been officially defined as a unit of mass and defined in relation to the kilogram since 1893, but its value in relation to the kilogram was altered slightly in 1894, and again to its current value in 1959 (which only differs from the 1894 definition by approximately one part in 10 million). In the United Kingdom, the avoirdupois pound was defined as a unit of mass by the Weights and Measures Act of 1878, but having a very slightly different value (in relation to the kilogram) than it does now, of approximately 0.453592338 kg. (This was a measured quantity, with the independently maintained artifact still serving as the official standard for this pound.) This old value is sometimes called the imperial pound, and this definition and terminology are obsolete unless referring to the slightly-different 1878 definition. There are 16 ounces in a pound (avoirdupois). This pound is equal to exactly 7000 grains, where a grain (measure) is exactly 0.06479891 gram. This relationship between avoirdupois pounds and troy grains has held true since the avoirdupois pound was redefined in terms of the troy units in the reign of Henry VIII, abandoning independent standards which had been measured as about 7002 grains troy. Since then, the grain has often been considered as a part of the avoirdupois system as well, even though it does not fit very well in that system. === Troy pound === ''Main article: Troy weight'' A troy pound, named for the French market town of Troyes in France where English merchants traded at least as early as the time of Charlemagne (early ninth century), was the mass unit used in England by apothecaries and jewelers. In Canada, Australia, the United Kingdom, and other places the unit is no longer a legal unit for trade, but its ounce subdivision enjoys a specific exemption from their metrication laws. The troy pound is a unit of mass equalling exactly 0.3732417216 kilograms. There are 12 troy ounces in a troy pound. A troy pound is equal to exactly 5760 grain (measure), making a troy pound equal to exactly 144/175 pounds avoirdupois. The troy pound is now used only for measurements of precious metals such as gold, silver, and platinum, and sometimes gems such as opals. Most weight measurements of precious metals using pounds and ounces use troy pounds and ounces, even though it is not always explicitly stated that this is the case. Some notable exceptions are Encyclopædia Britannica (a U.S. encyclopedia for about a century now) which uses either avoirdupois pounds or troy ounces, likely never both in the same article (which would make an awkward system with 14 7/12 ounces to a pound), and King Tut's sarcophagus lid, which is often stated to have been 242 or 243 pounds (avoirdupois; when it is, much less commonly, stated as 296 pounds, then the pounds are troy). One troy pound = 12 troy ounces = 240 pennyweight = 5760 grains. A pennyweight was literally the weight of a penny, as adopted by Henry II of England (1154–1189). This was a sterling silver penny weighing 1/240 of a troy pound. === Metric pound === ''Main article: kilogram'' In many countries that use the SI, the pound (or its translation, for example, the German language ''Pfund'', the French language ''livre'', or the Dutch language ''pond'') is used as an informal term for half of a kilogram, therefore for this case the pound is 500 grams. In many cases, this was an official redefinition back in the 19th century, but its use is generally no longer officially sanctioned. These replaced hundreds of older pounds, for example, one of around 459 to 460 grams in Spain, Portugal, and Latin America; 498.1 g in Norway; and several different ones in what is now Germany. In the case of the Dutch language ''pond'', this was officially redefined as 1 kg, with an ounce of 100 g; the former has fallen out of use, and if the pound is used today it is likely the 500 g variety, but the 100 g ounce remains in limited use. Despite the use of the pound term persisting as a slang term no scale or measuring device exists in metric countries that measures in pounds. All scales are in grams and a pound must be determined by weighing the product in grams. Thus a pound is weighed out as 500 g. === Pound as a unit of weight === When a pound is called a "unit of weight", it is usually a unit of mass. This is always true for the term ''net weight'', for example. Pounds are also used for the force definitions of weight, in which the pound force is a unit of force equal to 4.448 newtons. That is the force due to gravity of a pound (avoirdupois) where the acceleration of gravity is 32.17405 ft/s². The troy units of weight are never units of force. Pounds-force are never used for ''net weight'', nor are they used for body weight in the medicine, in zoology, or in sports. ''Main article: pound-force'' ==Which one is meant?== If neither "avoirdupois" nor "troy" is specified, the international pound (avoirdupois) is meant and is by law the only proper definition in the United States, United Kingdom, and Canada; the troy pound has been officially abandoned in the United Kingdom. The valuation of precious metals on U.S. exchanges is specified as dollars per troy ounce, although the fact that the troy ounce is used is usually implied. In the context of vegetable and meat sales within metric countries, a metric pound (500 g) is usually implied. == Force, weight, and mass== Historically, the pound predates the understanding of the distinction between force and mass. Once that distinction became clear, it was natural to ask whether the pound should be construed as a unit of mass, or a unit of force (and weight, which is defined as the gravitational force acting on an object). But because the foot-pound-second systems are no longer used in science (and are gradually approaching extinction even in U.S. engineering work), many scientists today would be as bemused by this question as by the question of whether the shekel is a unit of mass or of force. In many contexts, there is a long history of considering the pound to be a unit of mass: * Pounds were primarily a measure of how much stuff people had, for the purposes of trade. We know what we use for those purposes today--the only pounds legal for trade anywhere in the world are those defined as units of mass exactly equal to 0.45359237 kg. * Mass-measuring weighing scales were the only weighing instruments anybody ever used before the 19th century. * Over time, the various keepers of the standards redefinedpounds in terms of the metric system (which has happened in case of the ''avoirdupois'' and ''troy pounds'' as well as the ''metric pounds''), they were defined in terms of the kilogram, not the dyne or the newton. * When units such as the British thermal unit are defined based on the pound, those pounds are units of mass just like the grams or kilograms used as the basis of the definition of calories. * On labels of products sold in the U.S., the pounds and ounces are units of mass, like the grams and kilograms which appear right alongside them. On the other hand, pounds are always to be construed as a unit of force in contexts such as these: * Thrust of rocket or jet engines in pounds-force. * Torque in foot-pounds or pound-feet. * Pressure in pounds per square foot or pounds per square inch. * Energy in foot-pounds. There are some contexts in which the word "weight" is customarily used in a misleading way: * In commerce, the terms "net weight," ''troy weight,'' and ''Carat (mass)'' actually refer to mass rather than weight. The pounds used for this purpose are units of mass. * The scientific terms "molecular weight," "atomic weight," and "formula weight" all actually refer to mass, which is why some now refer to "molecular mass," etc. If a "pound mole" is used, it is based on the pound as a unit of mass. There are three practical ways of doing calculations with mass and force in the fps systems (and other systems such as inch-pound-second systems not discussed here), which the following table summarizes and compares with the SI. {| border="1" cellpadding="4" cellspacing="0" !rowspan="2"| ||rowspan="2"| SI ||colspan="3"| fps |- ! gravitational || engineering || absolute |- ! unit of time | s || s || s || s |- ! unit of distance | m || ft || ft || ft |- ! unit of mass | kg || slug (mass) || pound || pound |- ! unit of force and weight | N || pound-force || pound-force || poundal |- ! Newton's second law | ''F = m·a'' || ''F = m·a'' || ''F = m·a/g''c || ''F = m·a'' |- ! weight of an object | ''W = m·g'' || ''W = m·g'' || ''W = m·g/g''c || ''W = m·g'' |} The absolute and gravitational fps systems are ''coherent'' systems of units which both share with the SI the advantage of avoiding needless complication in several of the formulas used, whereas the engineering fps system requires the introduction of the factor ''g''c, which is a dimensionless constant, defined as 32.17405 lb·ft/(lbf·s²) and approximately equal to the typical acceleration of gravity on Earth, in ft/s². This must be distinguished from the actual local value of ''g''. No one of the three fps systems is more correct than the other two. None of our ordinary measurements are made in the context of any of these specialized subsets of mechanical units, used only in calculations. Although the U.S. National Bureau of Standards[http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf] has defined the pound as a unit of mass, and the pound-force as a unit of force, this distinction is not widely recognized among working physicists, because the fps system has not been used in physics, even in the U.S., since the early 20th century. When giving data to be used in calculations, it is not a good idea to use the term ''pound'' without clarifying whether mass or force is intended. If force is what is meant, the symbol "lbf" or the term "pounds-force" can be used for clarification. For mass, one can specify "pounds-mass." ==Notes== It is primarily the United States which uses them today, though other places such as livestock markets in Canada do still sell cattle in cents per pound, even though they sell hogs in cents per kilogram (actually, it is most often quoted as dollars per hundred pounds and dollars per hundred kilograms). Copies of the standard pound in London were distributed to other locations, where they served as the local standard. These copies have the same mass at the new location, even though they exert a (slightly) different amount of force due to regional variations in the Earth's gravity. The standards for pounds always were standards of mass, not standards of force. ==External links== * History of the pound as a unit of mass: [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf U.S. National Institute of Standards and Technology Official Definition, showing history] * Official abbreviations and definitions: [http://physics.nist.gov/Pubs/SP811/appenB9.html#MASSinertia U.S. National Institute of Standards and Technology Special Publication 811] Customary units in the United States Imperial units Units of mass
It might be worth mentioning in this article that in France that I know of (and possibly other countries as well that use the metric system, although I only know of the French example), a "pound" is frequently used to describe 500 grams (or half a kilogram). (In France, one refers to a "livre" in this context). ---- More info: Pounds that I know of: * avoirdupois pound = 7000 grains (16 oz of 437.5 grains) * troy pound = 5760 grains (12 oz of 480 grains) * Tower pound = 5400 grains (12 oz of 450 grains, I think) * mercantile pound = 7200 grains (15 oz of 480 grains (same as troy)) The last three are all obsolete (nobody uses troy ''pounds'' today, though troy ''ounces'' are still in use for gold, etc.) Also, the section "Troy pound" says that a pennyweight is the weight of a penny in Henry II's time, and a fraction of a ''troy'' ounce, but in Henry II's time it would have been a ''Tower'' ounce, which is somewhat lighter -- the Tower pound was only replaced with the troy pound for monetary weights by Henry VIII (or maybe it was Henry VII; rather later than Henry II, anyway) ---- I read the linked article, and I've still got some problems with defining pound as mass. It seems like the governments that define a pound as mass do so just because they don't care to differentiate between the mass of an object and the force that gravity exerts on the mass. Maybe they'll come round once we get moon colonies started :-) Governments can make laws saying that dogs are actually cats, but my physics book says, :In the British system, the unit of force is the ''pound'' (or pound-force) and the unit of mass is the ''slug.'' The unit of acceleration is one foor per second squared, so :::1 pound = 4.448221615260 newtons. Webster's dictionary also specifies the aviordupois pound as a ''weight.'' -- User:Merphant :That it is called weight does not in any way imply that it is "not mass." :Those government officials not only care about the difference--but they are also a whole lot smarter than you are, and they use the definition appropriate for the circumstances. :Why in the world do you suppose governments bother to define a pound in the first place? When we buy and sell goods by "weight," we certainly should not measure some quantity which varies with the strength of the local gravitational field. We do not do so. We have never done so. That pound defined as 0.45359237 kg is the pound legal for commerce in the United States. Just as it should be--until they finally come to their senses and outlaw it, leaving only kilograms and their multiples and submultiples as the legal units for this purpose. :When that net weight appears on the label of some U.S. product, the pounds and ounces are, of course, every bit as much units of mass as the grams and kilograms which appear right alongside them. No manufacturer measures two different quantities for this purpose, measuring force for the figure in pounds and mass for the figure in kilograms. No manufacturer puts one "weight" on their products for sale in Barrow, Alaska, and a different "weight" on the same product when it is sold in Honolulu, Hawaii. Nor should they do so. :Note that nowhere in the world are newtons legal units for the sale of goods. Nowhere in the world are kilograms force legal units for the sale of goods. Nowhere in the world are pounds force legal units for the sale of goods. :This is the quite proper and legitimate original meaning of the word "weight," which entered Old English over 1000 years ago meaning the quantity measured with a balance. That quantity is mass, not force. It was used as a measure of how much stuff they had, for the purpose of trade. We still use the very same word, with the very same meaning, for the very same purposes today. :User:Gene Nygaard 16:14, 6 Dec 2004 (UTC) ---- There's lots of authoritative citations about the pound always being a mass at: These link to official legislation, history, and authoritative standards bureaus. The pound is a mass, and always has been (well, for over a century, at least.) http://futureboy.homeip.net/frinkdocs/faq.html#pound ---- I should note that my comment for the checkin to the article that read "It's not mass... if you think it is, provide references to any standards body that's defined it as a mass since 1893." were totally wrong. This should read, "It's not force/weight... if you think it is, provide references to any standards body that's defined it as anything but a mass since 1893." :If pounds are mass, then why does every (American) science text book says something like "You would weigh 42 ''pounds'' on Mars." It may not be what the standards body uses, but it is what people think. I also remember my physics professor saying that pound is a unit of weight. Now he may not be in concordance with the standards body, but it is common usage, which is what wikipedia should present?User:Mckaysalisbury 20:03, 24 Aug 2004 (UTC) ---- lbm should be mentioned, even if its use is not recommendable. It is used, see e.g. http://www.glossary.oilfield.slb.com/Display.cfm?Term=lbm%2Fbbl. -User:Patrick Indeed. In that case, we have to mention it; and also say that its use is not recommendable. Likewise, for example, writing "gm" as an abbreviation for gram. -- User:Tarquin 14:37 Dec 23, 2002 (UTC) :The pound is traditionally a unit of force and weight and is still often used in that sense. The unit was defined before people knew that mass and weight were two differnt things. For anyone who thinks a pound is always a mass, please explain the derived unit of torque, the ''foot-pound'', which is a product of a force and a length. The word ''pound'' remains quite ambiguous although, today, it is generally (but, by no means, always) used to mean a mass. User:Bluelion 19:26 Mar 23, 2003 (UTC) ::Pound is for mass, which is also the historic interpretation and definition (see historical weights and measures). Pound (for mass) is abbreviated ''lb''. Pound-force is abbreviated ''lbf''. And there is NO other abbrevitaion for a netric gram but g. Gram is a unit of mass only, always has been. (There used to be a pond unit for gram-force, but this is now totally obsolete). EOD. -- User:Egil 07:55 Mar 26, 2003 (UTC) :::No, pound is for weight historically, and AFAIK still is. Long ago, people weren't aware that mass and weight were different, of course. :::I was unaware that anyone thought of it as a mass measure. I edited the page to fix that, but undid the edit after reading the rest of the page and this discussion...someone should sort it out, though. -- User:Tacitus Prime :You could not be more wrong. Pound (lb) historically is both a force and a mass; it always has been and it still is. Drawbar pull of a railroad locomotive, expressed in pounds, is not a mass, for example. There are many others. I notice that the historical weights and measures article you referenced has a lot of empty spaces - needs to be filled in. User:Bluelion 12:53 Mar 30, 2003 (UTC) ::This is historically totally wrong: If anything, pound was at the outset a unit of mass AND a monetary unit. The pound for force must have crept in gradually in the 1700s or thereabouts, but in modern usage it has again become important to separate the two. In modern correct usage (to the degree use of the "pound" unit can be considered "modern") pound as a force is pound-force or lbf. The online EB defines "pound" as ''unit of avoirdupois weight, equal to 16 ounces, 7,000 grains, or 0.4536 kilograms, and of troy and apothecaries' weight, equal to 12 ounces, 5,760 grains, or 0.37 kg. The Roman ancestor of the modern pound, the libra, is the source of the abbreviation lb. In early England several derivations of the libra vied for general acceptance.'' -- User:Egil 05:14 Mar 31, 2003 (UTC) :"If anything, pound was at the outset a unit of mass AND a monetary unit." :Funny, I would have thought it was a weight and a monetary unit. To say it was a mass is revisionist history. If the question is what is 'proper' today, then I have no problem with saying that ''pound'' means mass. But saying that, in common usage, that is all it means is a crock. And saying that that is what it has meant historically is also a crock. Before about the middle of the 20th century, I'm quite sure it meant both a force and a mass (yes, I'm that old). And, at that time, I'd bet the prevailing opinion was that it was a force. In recent years there's been quite a campaign by the protectors of all that is good and Holy to get it to mean a mass but, historically, it was both a mass and a force. Unless all the books I have that use the abbreviation ''lb'' to represent a force don't exist, and unless the education I got in engine school didn't happen, and unless psi represents a mass per unit area, then the word ''pound'' is ambiguous. It means either ''lbm.'' or ''lbf.''; we can't be sure unless we know the context. It's a lot like the word ''billion'' in that respect. User:Bluelion 03:19 Apr 1, 2003 (UTC) FWIW, I remember physics exam questions from school (early '80s) dealing with converting kilograms to pounds on the moon, etc., i.e., taking pounds to be ''weight'', not mass (that was an American school). Also, my old physics 101 text (Physics, Paul Tipler, 1982) defines a pound as a weight/force. Seems to me, to people who really care about the difference, it's a weight; those who say it's a mass probably don't know the difference :) --- --Use of Imperial Pound-- The definition of the imperial pound as "obsolete" needs clarification as the unit is still a de facto, if not official, measurment used more frequently than metric in many areas in the United Kingdom. An example is that of measuring the weight of a person in Stones (units of 14ibs) and Pounds and virtually all medical forms completed by patients recognise this practise by allowing the use of either metric or imperial. It is not simply an allowance for older people and feet and inches are used equally for human measurment in everyday situations. Also in boxing arenas the weight of the fighter would never be anounced to the crowd in Kg It would either be in Stones/pounds, or Stones/pounds and Pounds alone where there is likely to be a transatlantic audience for a British boxer. == POV problems == This article had some serious POV problesm, and I think it mostly fixed it. I know it's not perfect so feel free to make stuff look right. if anyone has some serious griefs with my expressing pounds as weight as the de facto standard, lets discuss itUser:Mckaysalisbury 08:33, 13 Nov 2004 (UTC) :Hi McKay -- Could you explain more about what you mean? I'm actually fairly happy with the article as it stands. I'm not sure it's accurate to say that layment consider it a unit of weight; laymen actually don't understand the distinction between mass and weight. --User:Bcrowell 01:54, 15 Nov 2004 (UTC) ::How much do you weigh? It's a completely serious question. I doubt that you would express your answer in newtons or say that your mass is 42 kilos. While some (women) won't want to tell you, or will lie. Any ''answer'' you get (in the United States), scientist or not, will be expressed in pounds. That's basically it. The Pound as a unit of weight is the ''de facto'' standard. ::You also make the claim that the layman doesn't know the difference between mass and weight, and while there are a whole lot of people who don't, I would say that most "laymen" do. They teach this stuff in elementary school science classes. My little sister of 10 knows the difference, but she doesn't think that pounds are a unit of mass. When I was in elementary school science classes, I did a report on Saturn. At that time I could tell you how much you weighed on Saturn. (I forget the multiplier now, it might be in the Saturn article. I don't care to check. Mars is 0.6, Moon is 1/6? ) Such a distinction ''requires'' knowledge of the difference, or at the very least, a knowledge of the ''proper'' understanding of the weight concept (even if the mass concept is unknown). User:Mckaysalisbury 03:42, 15 Nov 2004 (UTC) :::Hmm...I teach college physics, and I wish all my students understood this distinction, coming into my class, from elementary school science. My experience is that almost none of them do. If you ask someone in the U.S. what his weight is, he'll answer in pounds. If you ask someone elsewhere in the world, he'll answer in kilograms. Since the kilogram is undeniably a unit of mass, not weight, I think that demonstrates that the typical person does not understand that there is even a distinction between the two quantities. As a physicist, I think the current state of the article does a fairly good job of discussing how these terms are understood by physicists. What I think would help immensely would be if we could get some contributions from someone who is an engineer in the U.S., and does calculations using the fps system; they are basically the last people in the world who actually calculate things using Newton's laws in the fps system. The NBS article is, to my mind, almost irrelevant, because I know it doesn't represent a clear consensus among physicists, and I suspect it doesn't represent a consensus among U.S. engineers either. A government proclamation can't change the meaning of a word unless it actually matches the way people use the word. I'm still a little unclear about what you meant by POV issues; to me this does not seem to be an issue relating to POV/NPOV, but maybe I'm misunderstanding you. --User:Bcrowell 19:34, 15 Nov 2004 (UTC) ::::Just as ''pressure'' and ''stress'' have different meanings in physics class from what they mean in a psychology class, ''weight'' has different meanings in different fields. Sure, in physics and engineering ''weight'' means "gravitational force", but in commerce and law it means "mass". When something is sold by weight or by the pound, it's mass and the pound-mass that are being used: it's the amount of the substance that's of interest, not how hard it presses against the ground. Likewise when someone measures body weight to assess health or attractiveness, it's how much matter is in the body that is concerned: being overweight would be just as unhealthy in a low-gravity environment. Body weight is measured in pounds-mass. In fact I can't think a "layman" use of pounds that are pounds-force (except if you consider torque in foot pounds and pressure in pounds per square inch as "layman" uses). It would end a lot of ambiguity if everybody quit using the word ''weight'' completely, replacing with "gravitational force" or "mass" as appropriate, but that's not likely to happen. Just as a government can't change the meaning of a word, neither can authors of physics textbooks change the meaning of word outside their field. User:Indefatigable 23:06, 15 Nov 2004 (UTC) ::::You see the facts pretty well, Bcrowell--you just appear to have some great difficulty understanding what you know. Yes, kilograms are indeed used for body weight throughout the world, including many hospitals in the United States. And they are indeed the proper SI units for this purpose, as NIST tells us in the external reference on the article page, at [http://physics.nist.gov/Pubs/SP811/sec08.html] :::::Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of". :::::Examples: the child's weight is 23 kg :::::: the briefcase weighs 6 kg :::::: Net wt. 227 g ::::It is your failure to understand that the pounds also used for this purpose in the United States, when used in either the medical sciences or in sports--the primary reasons we weigh ourselves--are the pounds legally defined as units of mass equal to 0.45359237 kg exactly. ::::Naturally, if you have been miseducated (as your students likely have been), told that pounds are not units of mass, you have to resort to such a faulty explanation. You imagine a discordance between the use of pounds for weight and the use of kilograms for weight which does not exist. Your major problem is a failure to understand the simple fact that "weight" is an ambiguous word, and it is compounded by your failure to understand the simple fact that pounds are and always have been primarily units of mass, not force. (The pound force is such a recent bastardization that it is uniquely identified by that name. There is no troy pound force, for example. There is no metric pound force.) ::::The Body Mass Index is also properly named. It is weight in kilograms divided by the square of height in meters. Or you often see it expressed in terms of weight in pounds and height in inches, with a conversion factor added. That conversion factor is always a constant (because of rounding, different people might use different values--but each author only uses one value). The exact number used in the Wikipedia article at the time I write this is 703.07, which is clearly too many digits to be used for pounds force without specifying a location--but one correct to that many digits for the pounds we do use. Nobody ever uses a variable dependent upon latitude and altitude in this context, which it would have to be if your mistaken belief that the pounds used for this purpose in the medical sciences are pounds force were true. ::::Note also that hospitals which have scales which can measure in either pounds or kilograms (it is often the same scale) do not use different methods to calibrate them for the measurement in pounds from the methods they use to calibrate them for the measurement in kilograms. It is a constant conversion factor between the two, whether it is accomplished by flipping the bar on a balance beam to get a different set of detents for the movable weights, or a constant conversion factor programmed into a microchip. ::::Note that the pennyweight, like the troy ounce or troy pound, is always a unit of mass. Similarly, the hundredweight (even for those who think hundred is written in digits as "112") and the stone (1/8 of a long hundredweight, still used for body weight in the U.K.), unlike the pounds on which they are based, have not spawned units of force of the same name. ::::Here's American Society for Testing and Materials, Standard for Metric Practice, E 380-79, ASTM 1979: "3.4.1.2 Considerable confusion exists in the use of the term weight as a quantity to mean either force or mass. In commercial and everyday use, the term weight nearly always means mass; thus, when one speaks of a person's weight, the quantity referred to is mass. . . . When the term is used, it is important to know whether mass or force is intended and to use SI units properly as described in 3.4.1.1, by using kilograms for mass or newtons for force." ::::BTW, it is also not true that kilograms are "undeniably units of mass, not weight" because the kilogram is usually a unit of mass when it is a unit of weight. But furthermore, changing your last word to "force" wouldn't matter either. The kilogram-force was a quite legitimate unit (also known by another name even, the "kilopond") before the introduction of SI in 1960. There were even coherent systems of units devised with the kilogram force as a base unit of force, with the derived unit of mass the kgf s^2/m, known by several different names such as slug (mass), TME from a German acronym, metric slug, or mug, because this wonderful invention recurred to several different people bound and determined to show that those using metric units can be every bit as silly as those using English units. We still see far too many vestiges of the use of these obsolete kilogram-force--but rarely for anything called "weight" in anybody's book, in any of the various different meanings of this ambiguous word. We see them used for thrust of jet and rocket engines, for tension of bicycle spokes even in the U.S.A., for pressure gauges in "kg/cm²", for torque wrenches in "meter-kilograms", etc. Nobody calls those forces weight. OTOH, the kilograms that are used for body weight of humans, or of other animals as well in fields such as zoology and veterinary medicine, and the kilograms that are used for "net weight" of anything are always units of mass, not force. ("Net weight" is not a physics term.) ::::The worst of it, however, Bcrowell, is that I suspect that you are not merely a physics teacher, but also a textbook author--of a textbook distributed primarily on the Internet, no less--who has spread his misconceptions in this field far beyond his own classroom. ::::User:Gene Nygaard 17:26, 6 Dec 2004 (UTC) -------- :::::I agree with Gene Nygaard here. The entire section added about force, weight, and mass confuses the issue, and is very poorly written. And of course the pound is only a unit of mass, and has been clearly defined as only a mass by all standards bodies and legislative definitions in all countries for well over a century. I'd recommend that the entire force, weight, and mass section be removed. It's meandering, wrong, and only comes from one person's very confused misconceptions. :::::In addition, I bristle at any article that says "but physicists/laymen/(insert other confused group) take it to mean something different" and then explain only their own confused, baseless misunderstandings. All such parts should be removed. People don't come to Wikipedia to find out about what some clueless people believe--they come to find out what's actually ''right''. The standards bodies (and even legislatures) that created these definitions well over a century ago clearly understood the difference between mass and weight, and differentiated them unambiguously. Too bad those who teach our kids don't. --User:Eliasen 08:22, 9 Jan 2005 (UTC) ::::::Sounds fine with me. User:Elf | User talk:Elf 18:48, 9 Jan 2005 (UTC) ::::::Eliasen, you know darned well that pounds are also units of force. Why are you trying to bury your head in the sand? ::::::Most of the information on the pound-force and its definitions and use belongs in the article of that name, but it needs to be mentioned here as well. ::::::It is very important to retain discussions involving the ambiguous word ''weight.'' There are far too many people who have gotten the mistaken notion that because a pound is a ''unit of weight'' it cannot be a ''unit of mass'' (a notion totally contrary to the fact that of all the pounds used throughout history, only one was also used as a ''unit of force'' to any significant extent). OTOH, we also have the confused people of Eliasen's class, insisting the opposite: that pounds are not ''units of force'' (even though from what I have seem, he or she appears not to understand the ambiguous nature of the word ''weight'' so the previously mentioned confusion would seem more probable). ::::::There are also far too many confused science professors in our colleges and universities, and high school teachers and the authors of some of the textbooks they use, filling the heads of students with the nonsense idea that they should measure "their weight" in newtons rather than kilograms or pounds. (And most everybody gets somewhat confused about this—and quite understandably so—failing to understand that the ''pounds'' used for this purpose in medicine and sports are units of mass, and that the ''pounds'' used for this purpose in many science textbooks, science museum exhibits, and other discussions of "your weight on other planets" are pound-force.) ::::::There are far too many professors and textbook authors who imagine themselves to be cheesemongers or purveyors of sugar, potatoes, bananas, or whatever, who do not understand that the kilograms used for that purpose—and, most important to this article, the pounds and ounces which appear right alongside them on labels in the United States—are units of mass, not units of force. I guess they must think that talking about the sale of cheese in a physics class can somehow magically change the rules—and they are the proper rules—governing its sale. (Of those who think the pounds are units of force, some think the kilograms are units of force as well, and others imagine some weird statement of measurements of two different quantities on the labels.) User:Gene Nygaard 13:40, 11 Jan 2005 (UTC) :::::::Let me be clear. The pound is a unit of mass. The pound-force is a unit of force, but that is ''not'' the pound. I have never said otherwise. Gene, do you have references by any standards body from any country in the past century that says that the pound is a force? If so, please produce it, otherwise, we should drop the whole force sections, which are in error. I don't want a confused colloquial usage, nor an industry shorthand, but an official standard by a national or international standards body. Say, since 1878 in the UK or 1893 in the U.S.? If so, we can maybe re-open this discussion, but it's been quite clear for a long, long time to all standards bodies (and even legal bodies, except for a minor confusion in Canada's legislative heading of the section of law that defines the pound.) Again, I have placed further references for a wide variety of countries and standards bodies http://futureboy.homeip.net/frinkdocs/faq.html#pound here. Do you dispute any of these countries' definitions? :::::::Gene, why do you say that people shouldn't measure their weight in newtons? That is, in fact, totally appropriate. Do you not agree that a newton is a force and that is indeed what is measured by almost all scales? If they're indicating their mass, it should be in kilograms or pounds. Weight is, obviously, not invariant under different accelerational frames, but newtons (or pounds-force) are quite appropriate to measure this varying quantity. I don't know where the confusion lies in your understanding. :::::::I agree that discussion of the pound-force should be in this article. In fact, I believe I put discussion of the pound-force in originally and linked to the pound-force article. It was simple, concise, and sufficient to show the difference. I will reiterate my opinion that any encyclopedia should focus unambiguously on ''correct'' usage, not confuse the issue with enumerating the endless permutations of incorrect colloquial usage. That isn't what an article on the pound should be about. :::::::I do believe that if people are confused about the difference between force/weight and mass, then that should be an entirely separate article, and not crammed into the article about the pound, otherwise it will be duplicated among all articles about mass or weight. This article needs cleanup badly. --User:Eliasen 08:29, 17 Jan 2005 (UTC) ::::::::I'll number my comments to correspond to your paragraphs 1-4. ::::::::1. Even if standards bodies had defined a "pound-force" that would not mean that pounds are not units of force. Any time you define something as a noun-adjective combination, it is logical and reasonable to expect that the adjective will sometimes be dropped. ::::::::However, since standards bodies haven't bothered to define pounds-force, even that is irrelevant. The existence of the pound as a unit of force, whether it is called just a pound, or by the old name "pound-weight" (which at least one old engineering textbook used to mean the geepound or slug, a unit of mass, instead), or the "pound-force" is determined by usage, not by standards bodies who have not acted. Various standards bodies have, of course, recognized the existence of pounds force. See, for example, the footnote 24 in NIST's appendix of conversion factors in SP811, giving a conditional definition of the pound-force. [http://physics.nist.gov/Pubs/SP811/footnotes.html#f24] ::::::::The main reason I brought that point up was to make sure that those reading this Talk page know what you know. You had written it like you were a dummy who didn't know pounds-force exist; whereas you merely intended to write it like a dummy who didn't know that they are called "pounds." ::::::::2. Show us some examples of the use of pounds-force for body weight (keeping in mind that you are the one claiming that pounds are not units of force if they are not identified as such). Better yet, show us all the examples you can find, from all around the world, of people using newtons rather than kilograms for body weight of humans, or of other animals as well in the veterinary or zoological sciences, for that matter. ::::::::"[M]easured on almost all scales?" So what happens when you get serious about your weight, and go to the doctor's office or the gym, and weigh yourself on one of those platform-type beam balances? Isn't that a better indication of what you want to measure, than a substitute considered acceptable in many homes because it is cheaply made? Furthermore, those cheap bathroom scales didn't even exist until 1937, well within the lifetime of many people living today. Those spring scales are no more accurate in measuring force than they are in measuring the mass at the location in which they are used. ::::::::How about those old scales that used to be seen in public places, where you could put in a penny and get your fortune told, as well as your Honest Weight: No Springs? ::::::::"[M]easured on almost all scales?" In a hospital, where they are concerned about not having discrepancies between the scales in different departments, or when someone is transferred to a different hospital, how are those scales calibrated? ::::::::Here are some of your "standards bodies" on this point. ASTM International, Standard for Metric Practice, E 380-79, ASTM 1979: ::::::::* 3.4.1.2 Considerable confusion exists in the use of the term weight as a quantity to mean either force or mass. In commercial and everyday use, the term weight nearly always means mass; thus, when one speaks of a person's weight, the quantity referred to is mass. ::::::::NIST [http://physics.nist.gov/Pubs/SP811/sec08.html#8.3 ''Guide for the Use of the International System of Units (SI),'' section 8.3] ::::::::*Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of." :::::::::Examples: the child's weight is 23 kg :::::::: 3. You don't even have any clear-cut, universal rules for the use of pounds force (or, for that matter, of English units in general), and not much from any standards organizations in the way of any guidance in their use, so even though I disagree with your philosophy here, it is irrelevant. :::::::: 4. The confusion most often seen in this regard, the confusion specifically mentioned by many standards organizations, is the confusion you seem to share (based on your "force/weight" and "mass" dichotomy, as well as your discussion about teachers in an earlier comment) with many (other?) science teachers—the failure to understand the simple fact that ''weight'' is an ambiguous word, one with several different meanings. Just remember this to help keep it straight in your mind: in the troy weight there are no ''troy-ounces-force'' and no ''troy-pounds-force''. :::::::: You've seen on this talk page, and on edits to the article itself, how this confusion about ''weight'' is the root cause of many peoples' beliefs that pounds cannot be units of mass. Even if it is discussed adequately (and relatively permanently, by Wikipedia standards) in another article, a good, strong summary accompanied with a link to that discussion is important in this article. ::::::::User:Gene Nygaard 15:02, 17 Jan 2005 (UTC) --------- :::McKay, I hope that little sister runs into better teachers. Soon. :::Maybe you could point her to the discussion on this page. :::User:Gene Nygaard 10:43, 8 Dec 2004 (UTC) ---------- ''...which is a dimensionless constant, defined as 32.17405 lb ft/(lbf s2) and approximately equal to the typical acceleration of gravity on Earth, in ft/s2.'' Is the use of the word ''dimensionless'' appropriate here? :It could probably be worded better (mea culpa), but it is indeed ''dimensionless'' though it is not ''unitless''. See dimensional analysis (a link to that in connection to the quoted statement might be helpful). As that says, a dimension is "the type of unit needed to express it"; for example, ''feet'' and ''meters'' have the same ''dimension'', something that in this context is usually called "length", often symbolized ''L''. Other dimensions involved here can be called "time" ''T'' and "mass" ''M'' (other "dimensions" could be chosen, for example force rather than mass, with the same end result). Let's do the dimensional analysis of those units: unit dimension lb ''M'' ft ''L'' lbf = 32 lb·ft/s² ''M'' ''L'' ''T''-2 s² ''T''2 and then combining them for overall dimensions, lb ft/(lbf s²) = lb ft lbf-1 s-2, so the dimensions are: (''M''1)(''L''1)(''M''-1 ''L''-1 ''T''+2)(''T''-2) =
''M''0 ''L''0 ''T''0 (i.e., dimensionless) :Now do the dimensional analysis of a formula involving this ''gc'' and you will see that the units as they are expressed in the quote above are indeed the correct units. Note the distinction made in the article between this conversion factor used in formulas, something called ''gc'', and the standard acceleration of gravity, ''gn'' = 32.174 ft/s², which has dimensions of acceleration, or ''L'' ''T''-2. User:Gene Nygaard 14:16, 27 Jan 2005 (UTC) ::You're right, of course. Thank you for the explanation. Having been brought up on SI I'm not used to these conversion numbers. Somehow, it feels a bit less dimensionless than some numbers, though. ;-) Possibly the wording could be improved by changing ''...and approximately equal to the typical acceleration...'' to ''...and numerically equal to the typical acceleration...''. I was confused by the units on the acceleration and assumed that the units on ''gc'' cancelled to the same.
-- User:Infrogmation 01:30, 5 Mar 2005 (UTC)
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Words begining with Pound:
Pound
Pound
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Pound-force_per_square_inch
Pound-force_per_square_inch
Poundal
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Pound_(disambiguation)
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Pound_(town),_Wisconsin
Pound_(village),_Marinette_County,_WI
Pound_(village),_Marinette_County,_Wisconsin
Pound_(village),_WI
Pound_(village),_Wisconsin
Pound_and_mil
Pound_and_mill
Pound_avoirdupois
Pound_cake
Pound_force
Pound_for_pound
Pound_Hill
Pound_Hill,_Crawley
Pound_House
Pound_it
Pound_key
Pound_mass
Pound_per_square_inch
Pound_Puppies
Pound_Ridge
Pound_Ridge,_New_York
Pound_Scots
Pound_sign
Pound_Sterling
Pound_Sterling
Pound_sterling
Pound_sterling
Pound_stirling
Pound
Officially the pound is the name for at least three different physical units of mass: * The pound (avoirdupois). * The troy pound. * The metric pound, no longer officially sanctioned but still in informal use in some places. Standards bodies define the pound as a unit of mass, which are the pounds most people in everyday usage use as a ''unit of weight''. ==Origins== The Latin word ''libra'' describes a Roman unit of weight similar to a pound, and the abbreviation "lb" for the unit of weight and the signs £ and ₤ (crossed-out L's) for the currency derived from this. The word "pound" itself comes from the Latin ''pendere'', to weigh, while ''libra'' meant "weighing scale". == Measurement systems == In the Imperial units (often referred to as the pound-inch system, or ''the English system'' in the United States) there are two basic pounds defined, and also an obsolete definition of one variant of the pound. === Pound (avoirdupois) or international pound === ''Main article: avoirdupois'' The avoirdupois pound was invented by London merchants in 1303. The pound (avoirdupois) or international pound, abbreviation "lb" or sometimes number sign in the United States, is the mass unit defined as exactly 0.45359237 kilograms (or 453.59237 grams). This definition has been in effect since a 1959 agreement among the national standards laboratories of the United States, Canada, the United Kingdom, South Africa, Australia, and New Zealand. [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf] It is part of the avoirdupois system of mass units. In the United States, the pound has been officially defined as a unit of mass and defined in relation to the kilogram since 1893, but its value in relation to the kilogram was altered slightly in 1894, and again to its current value in 1959 (which only differs from the 1894 definition by approximately one part in 10 million). In the United Kingdom, the avoirdupois pound was defined as a unit of mass by the Weights and Measures Act of 1878, but having a very slightly different value (in relation to the kilogram) than it does now, of approximately 0.453592338 kg. (This was a measured quantity, with the independently maintained artifact still serving as the official standard for this pound.) This old value is sometimes called the imperial pound, and this definition and terminology are obsolete unless referring to the slightly-different 1878 definition. There are 16 ounces in a pound (avoirdupois). This pound is equal to exactly 7000 grains, where a grain (measure) is exactly 0.06479891 gram. This relationship between avoirdupois pounds and troy grains has held true since the avoirdupois pound was redefined in terms of the troy units in the reign of Henry VIII, abandoning independent standards which had been measured as about 7002 grains troy. Since then, the grain has often been considered as a part of the avoirdupois system as well, even though it does not fit very well in that system. === Troy pound === ''Main article: Troy weight'' A troy pound, named for the French market town of Troyes in France where English merchants traded at least as early as the time of Charlemagne (early ninth century), was the mass unit used in England by apothecaries and jewelers. In Canada, Australia, the United Kingdom, and other places the unit is no longer a legal unit for trade, but its ounce subdivision enjoys a specific exemption from their metrication laws. The troy pound is a unit of mass equalling exactly 0.3732417216 kilograms. There are 12 troy ounces in a troy pound. A troy pound is equal to exactly 5760 grain (measure), making a troy pound equal to exactly 144/175 pounds avoirdupois. The troy pound is now used only for measurements of precious metals such as gold, silver, and platinum, and sometimes gems such as opals. Most weight measurements of precious metals using pounds and ounces use troy pounds and ounces, even though it is not always explicitly stated that this is the case. Some notable exceptions are Encyclopædia Britannica (a U.S. encyclopedia for about a century now) which uses either avoirdupois pounds or troy ounces, likely never both in the same article (which would make an awkward system with 14 7/12 ounces to a pound), and King Tut's sarcophagus lid, which is often stated to have been 242 or 243 pounds (avoirdupois; when it is, much less commonly, stated as 296 pounds, then the pounds are troy). One troy pound = 12 troy ounces = 240 pennyweight = 5760 grains. A pennyweight was literally the weight of a penny, as adopted by Henry II of England (1154–1189). This was a sterling silver penny weighing 1/240 of a troy pound. === Metric pound === ''Main article: kilogram'' In many countries that use the SI, the pound (or its translation, for example, the German language ''Pfund'', the French language ''livre'', or the Dutch language ''pond'') is used as an informal term for half of a kilogram, therefore for this case the pound is 500 grams. In many cases, this was an official redefinition back in the 19th century, but its use is generally no longer officially sanctioned. These replaced hundreds of older pounds, for example, one of around 459 to 460 grams in Spain, Portugal, and Latin America; 498.1 g in Norway; and several different ones in what is now Germany. In the case of the Dutch language ''pond'', this was officially redefined as 1 kg, with an ounce of 100 g; the former has fallen out of use, and if the pound is used today it is likely the 500 g variety, but the 100 g ounce remains in limited use. Despite the use of the pound term persisting as a slang term no scale or measuring device exists in metric countries that measures in pounds. All scales are in grams and a pound must be determined by weighing the product in grams. Thus a pound is weighed out as 500 g. === Pound as a unit of weight === When a pound is called a "unit of weight", it is usually a unit of mass. This is always true for the term ''net weight'', for example. Pounds are also used for the force definitions of weight, in which the pound force is a unit of force equal to 4.448 newtons. That is the force due to gravity of a pound (avoirdupois) where the acceleration of gravity is 32.17405 ft/s². The troy units of weight are never units of force. Pounds-force are never used for ''net weight'', nor are they used for body weight in the medicine, in zoology, or in sports. ''Main article: pound-force'' ==Which one is meant?== If neither "avoirdupois" nor "troy" is specified, the international pound (avoirdupois) is meant and is by law the only proper definition in the United States, United Kingdom, and Canada; the troy pound has been officially abandoned in the United Kingdom. The valuation of precious metals on U.S. exchanges is specified as dollars per troy ounce, although the fact that the troy ounce is used is usually implied. In the context of vegetable and meat sales within metric countries, a metric pound (500 g) is usually implied. == Force, weight, and mass== Historically, the pound predates the understanding of the distinction between force and mass. Once that distinction became clear, it was natural to ask whether the pound should be construed as a unit of mass, or a unit of force (and weight, which is defined as the gravitational force acting on an object). But because the foot-pound-second systems are no longer used in science (and are gradually approaching extinction even in U.S. engineering work), many scientists today would be as bemused by this question as by the question of whether the shekel is a unit of mass or of force. In many contexts, there is a long history of considering the pound to be a unit of mass: * Pounds were primarily a measure of how much stuff people had, for the purposes of trade. We know what we use for those purposes today--the only pounds legal for trade anywhere in the world are those defined as units of mass exactly equal to 0.45359237 kg. * Mass-measuring weighing scales were the only weighing instruments anybody ever used before the 19th century. * Over time, the various keepers of the standards redefinedpounds in terms of the metric system (which has happened in case of the ''avoirdupois'' and ''troy pounds'' as well as the ''metric pounds''), they were defined in terms of the kilogram, not the dyne or the newton. * When units such as the British thermal unit are defined based on the pound, those pounds are units of mass just like the grams or kilograms used as the basis of the definition of calories. * On labels of products sold in the U.S., the pounds and ounces are units of mass, like the grams and kilograms which appear right alongside them. On the other hand, pounds are always to be construed as a unit of force in contexts such as these: * Thrust of rocket or jet engines in pounds-force. * Torque in foot-pounds or pound-feet. * Pressure in pounds per square foot or pounds per square inch. * Energy in foot-pounds. There are some contexts in which the word "weight" is customarily used in a misleading way: * In commerce, the terms "net weight," ''troy weight,'' and ''Carat (mass)'' actually refer to mass rather than weight. The pounds used for this purpose are units of mass. * The scientific terms "molecular weight," "atomic weight," and "formula weight" all actually refer to mass, which is why some now refer to "molecular mass," etc. If a "pound mole" is used, it is based on the pound as a unit of mass. There are three practical ways of doing calculations with mass and force in the fps systems (and other systems such as inch-pound-second systems not discussed here), which the following table summarizes and compares with the SI. {| border="1" cellpadding="4" cellspacing="0" !rowspan="2"| ||rowspan="2"| SI ||colspan="3"| fps |- ! gravitational || engineering || absolute |- ! unit of time | s || s || s || s |- ! unit of distance | m || ft || ft || ft |- ! unit of mass | kg || slug (mass) || pound || pound |- ! unit of force and weight | N || pound-force || pound-force || poundal |- ! Newton's second law | ''F = m·a'' || ''F = m·a'' || ''F = m·a/g''c || ''F = m·a'' |- ! weight of an object | ''W = m·g'' || ''W = m·g'' || ''W = m·g/g''c || ''W = m·g'' |} The absolute and gravitational fps systems are ''coherent'' systems of units which both share with the SI the advantage of avoiding needless complication in several of the formulas used, whereas the engineering fps system requires the introduction of the factor ''g''c, which is a dimensionless constant, defined as 32.17405 lb·ft/(lbf·s²) and approximately equal to the typical acceleration of gravity on Earth, in ft/s². This must be distinguished from the actual local value of ''g''. No one of the three fps systems is more correct than the other two. None of our ordinary measurements are made in the context of any of these specialized subsets of mechanical units, used only in calculations. Although the U.S. National Bureau of Standards[http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf] has defined the pound as a unit of mass, and the pound-force as a unit of force, this distinction is not widely recognized among working physicists, because the fps system has not been used in physics, even in the U.S., since the early 20th century. When giving data to be used in calculations, it is not a good idea to use the term ''pound'' without clarifying whether mass or force is intended. If force is what is meant, the symbol "lbf" or the term "pounds-force" can be used for clarification. For mass, one can specify "pounds-mass." ==Notes== It is primarily the United States which uses them today, though other places such as livestock markets in Canada do still sell cattle in cents per pound, even though they sell hogs in cents per kilogram (actually, it is most often quoted as dollars per hundred pounds and dollars per hundred kilograms). Copies of the standard pound in London were distributed to other locations, where they served as the local standard. These copies have the same mass at the new location, even though they exert a (slightly) different amount of force due to regional variations in the Earth's gravity. The standards for pounds always were standards of mass, not standards of force. ==External links== * History of the pound as a unit of mass: [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf U.S. National Institute of Standards and Technology Official Definition, showing history] * Official abbreviations and definitions: [http://physics.nist.gov/Pubs/SP811/appenB9.html#MASSinertia U.S. National Institute of Standards and Technology Special Publication 811] Customary units in the United States Imperial units Units of mass
Pound
It might be worth mentioning in this article that in France that I know of (and possibly other countries as well that use the metric system, although I only know of the French example), a "pound" is frequently used to describe 500 grams (or half a kilogram). (In France, one refers to a "livre" in this context). ---- More info: Pounds that I know of: * avoirdupois pound = 7000 grains (16 oz of 437.5 grains) * troy pound = 5760 grains (12 oz of 480 grains) * Tower pound = 5400 grains (12 oz of 450 grains, I think) * mercantile pound = 7200 grains (15 oz of 480 grains (same as troy)) The last three are all obsolete (nobody uses troy ''pounds'' today, though troy ''ounces'' are still in use for gold, etc.) Also, the section "Troy pound" says that a pennyweight is the weight of a penny in Henry II's time, and a fraction of a ''troy'' ounce, but in Henry II's time it would have been a ''Tower'' ounce, which is somewhat lighter -- the Tower pound was only replaced with the troy pound for monetary weights by Henry VIII (or maybe it was Henry VII; rather later than Henry II, anyway) ---- I read the linked article, and I've still got some problems with defining pound as mass. It seems like the governments that define a pound as mass do so just because they don't care to differentiate between the mass of an object and the force that gravity exerts on the mass. Maybe they'll come round once we get moon colonies started :-) Governments can make laws saying that dogs are actually cats, but my physics book says, :In the British system, the unit of force is the ''pound'' (or pound-force) and the unit of mass is the ''slug.'' The unit of acceleration is one foor per second squared, so :::1 pound = 4.448221615260 newtons. Webster's dictionary also specifies the aviordupois pound as a ''weight.'' -- User:Merphant :That it is called weight does not in any way imply that it is "not mass." :Those government officials not only care about the difference--but they are also a whole lot smarter than you are, and they use the definition appropriate for the circumstances. :Why in the world do you suppose governments bother to define a pound in the first place? When we buy and sell goods by "weight," we certainly should not measure some quantity which varies with the strength of the local gravitational field. We do not do so. We have never done so. That pound defined as 0.45359237 kg is the pound legal for commerce in the United States. Just as it should be--until they finally come to their senses and outlaw it, leaving only kilograms and their multiples and submultiples as the legal units for this purpose. :When that net weight appears on the label of some U.S. product, the pounds and ounces are, of course, every bit as much units of mass as the grams and kilograms which appear right alongside them. No manufacturer measures two different quantities for this purpose, measuring force for the figure in pounds and mass for the figure in kilograms. No manufacturer puts one "weight" on their products for sale in Barrow, Alaska, and a different "weight" on the same product when it is sold in Honolulu, Hawaii. Nor should they do so. :Note that nowhere in the world are newtons legal units for the sale of goods. Nowhere in the world are kilograms force legal units for the sale of goods. Nowhere in the world are pounds force legal units for the sale of goods. :This is the quite proper and legitimate original meaning of the word "weight," which entered Old English over 1000 years ago meaning the quantity measured with a balance. That quantity is mass, not force. It was used as a measure of how much stuff they had, for the purpose of trade. We still use the very same word, with the very same meaning, for the very same purposes today. :User:Gene Nygaard 16:14, 6 Dec 2004 (UTC) ---- There's lots of authoritative citations about the pound always being a mass at: These link to official legislation, history, and authoritative standards bureaus. The pound is a mass, and always has been (well, for over a century, at least.) http://futureboy.homeip.net/frinkdocs/faq.html#pound ---- I should note that my comment for the checkin to the article that read "It's not mass... if you think it is, provide references to any standards body that's defined it as a mass since 1893." were totally wrong. This should read, "It's not force/weight... if you think it is, provide references to any standards body that's defined it as anything but a mass since 1893." :If pounds are mass, then why does every (American) science text book says something like "You would weigh 42 ''pounds'' on Mars." It may not be what the standards body uses, but it is what people think. I also remember my physics professor saying that pound is a unit of weight. Now he may not be in concordance with the standards body, but it is common usage, which is what wikipedia should present?User:Mckaysalisbury 20:03, 24 Aug 2004 (UTC) ---- lbm should be mentioned, even if its use is not recommendable. It is used, see e.g. http://www.glossary.oilfield.slb.com/Display.cfm?Term=lbm%2Fbbl. -User:Patrick Indeed. In that case, we have to mention it; and also say that its use is not recommendable. Likewise, for example, writing "gm" as an abbreviation for gram. -- User:Tarquin 14:37 Dec 23, 2002 (UTC) :The pound is traditionally a unit of force and weight and is still often used in that sense. The unit was defined before people knew that mass and weight were two differnt things. For anyone who thinks a pound is always a mass, please explain the derived unit of torque, the ''foot-pound'', which is a product of a force and a length. The word ''pound'' remains quite ambiguous although, today, it is generally (but, by no means, always) used to mean a mass. User:Bluelion 19:26 Mar 23, 2003 (UTC) ::Pound is for mass, which is also the historic interpretation and definition (see historical weights and measures). Pound (for mass) is abbreviated ''lb''. Pound-force is abbreviated ''lbf''. And there is NO other abbrevitaion for a netric gram but g. Gram is a unit of mass only, always has been. (There used to be a pond unit for gram-force, but this is now totally obsolete). EOD. -- User:Egil 07:55 Mar 26, 2003 (UTC) :::No, pound is for weight historically, and AFAIK still is. Long ago, people weren't aware that mass and weight were different, of course. :::I was unaware that anyone thought of it as a mass measure. I edited the page to fix that, but undid the edit after reading the rest of the page and this discussion...someone should sort it out, though. -- User:Tacitus Prime :You could not be more wrong. Pound (lb) historically is both a force and a mass; it always has been and it still is. Drawbar pull of a railroad locomotive, expressed in pounds, is not a mass, for example. There are many others. I notice that the historical weights and measures article you referenced has a lot of empty spaces - needs to be filled in. User:Bluelion 12:53 Mar 30, 2003 (UTC) ::This is historically totally wrong: If anything, pound was at the outset a unit of mass AND a monetary unit. The pound for force must have crept in gradually in the 1700s or thereabouts, but in modern usage it has again become important to separate the two. In modern correct usage (to the degree use of the "pound" unit can be considered "modern") pound as a force is pound-force or lbf. The online EB defines "pound" as ''unit of avoirdupois weight, equal to 16 ounces, 7,000 grains, or 0.4536 kilograms, and of troy and apothecaries' weight, equal to 12 ounces, 5,760 grains, or 0.37 kg. The Roman ancestor of the modern pound, the libra, is the source of the abbreviation lb. In early England several derivations of the libra vied for general acceptance.'' -- User:Egil 05:14 Mar 31, 2003 (UTC) :"If anything, pound was at the outset a unit of mass AND a monetary unit." :Funny, I would have thought it was a weight and a monetary unit. To say it was a mass is revisionist history. If the question is what is 'proper' today, then I have no problem with saying that ''pound'' means mass. But saying that, in common usage, that is all it means is a crock. And saying that that is what it has meant historically is also a crock. Before about the middle of the 20th century, I'm quite sure it meant both a force and a mass (yes, I'm that old). And, at that time, I'd bet the prevailing opinion was that it was a force. In recent years there's been quite a campaign by the protectors of all that is good and Holy to get it to mean a mass but, historically, it was both a mass and a force. Unless all the books I have that use the abbreviation ''lb'' to represent a force don't exist, and unless the education I got in engine school didn't happen, and unless psi represents a mass per unit area, then the word ''pound'' is ambiguous. It means either ''lbm.'' or ''lbf.''; we can't be sure unless we know the context. It's a lot like the word ''billion'' in that respect. User:Bluelion 03:19 Apr 1, 2003 (UTC) FWIW, I remember physics exam questions from school (early '80s) dealing with converting kilograms to pounds on the moon, etc., i.e., taking pounds to be ''weight'', not mass (that was an American school). Also, my old physics 101 text (Physics, Paul Tipler, 1982) defines a pound as a weight/force. Seems to me, to people who really care about the difference, it's a weight; those who say it's a mass probably don't know the difference :) --- --Use of Imperial Pound-- The definition of the imperial pound as "obsolete" needs clarification as the unit is still a de facto, if not official, measurment used more frequently than metric in many areas in the United Kingdom. An example is that of measuring the weight of a person in Stones (units of 14ibs) and Pounds and virtually all medical forms completed by patients recognise this practise by allowing the use of either metric or imperial. It is not simply an allowance for older people and feet and inches are used equally for human measurment in everyday situations. Also in boxing arenas the weight of the fighter would never be anounced to the crowd in Kg It would either be in Stones/pounds, or Stones/pounds and Pounds alone where there is likely to be a transatlantic audience for a British boxer. == POV problems == This article had some serious POV problesm, and I think it mostly fixed it. I know it's not perfect so feel free to make stuff look right. if anyone has some serious griefs with my expressing pounds as weight as the de facto standard, lets discuss itUser:Mckaysalisbury 08:33, 13 Nov 2004 (UTC) :Hi McKay -- Could you explain more about what you mean? I'm actually fairly happy with the article as it stands. I'm not sure it's accurate to say that layment consider it a unit of weight; laymen actually don't understand the distinction between mass and weight. --User:Bcrowell 01:54, 15 Nov 2004 (UTC) ::How much do you weigh? It's a completely serious question. I doubt that you would express your answer in newtons or say that your mass is 42 kilos. While some (women) won't want to tell you, or will lie. Any ''answer'' you get (in the United States), scientist or not, will be expressed in pounds. That's basically it. The Pound as a unit of weight is the ''de facto'' standard. ::You also make the claim that the layman doesn't know the difference between mass and weight, and while there are a whole lot of people who don't, I would say that most "laymen" do. They teach this stuff in elementary school science classes. My little sister of 10 knows the difference, but she doesn't think that pounds are a unit of mass. When I was in elementary school science classes, I did a report on Saturn. At that time I could tell you how much you weighed on Saturn. (I forget the multiplier now, it might be in the Saturn article. I don't care to check. Mars is 0.6, Moon is 1/6? ) Such a distinction ''requires'' knowledge of the difference, or at the very least, a knowledge of the ''proper'' understanding of the weight concept (even if the mass concept is unknown). User:Mckaysalisbury 03:42, 15 Nov 2004 (UTC) :::Hmm...I teach college physics, and I wish all my students understood this distinction, coming into my class, from elementary school science. My experience is that almost none of them do. If you ask someone in the U.S. what his weight is, he'll answer in pounds. If you ask someone elsewhere in the world, he'll answer in kilograms. Since the kilogram is undeniably a unit of mass, not weight, I think that demonstrates that the typical person does not understand that there is even a distinction between the two quantities. As a physicist, I think the current state of the article does a fairly good job of discussing how these terms are understood by physicists. What I think would help immensely would be if we could get some contributions from someone who is an engineer in the U.S., and does calculations using the fps system; they are basically the last people in the world who actually calculate things using Newton's laws in the fps system. The NBS article is, to my mind, almost irrelevant, because I know it doesn't represent a clear consensus among physicists, and I suspect it doesn't represent a consensus among U.S. engineers either. A government proclamation can't change the meaning of a word unless it actually matches the way people use the word. I'm still a little unclear about what you meant by POV issues; to me this does not seem to be an issue relating to POV/NPOV, but maybe I'm misunderstanding you. --User:Bcrowell 19:34, 15 Nov 2004 (UTC) ::::Just as ''pressure'' and ''stress'' have different meanings in physics class from what they mean in a psychology class, ''weight'' has different meanings in different fields. Sure, in physics and engineering ''weight'' means "gravitational force", but in commerce and law it means "mass". When something is sold by weight or by the pound, it's mass and the pound-mass that are being used: it's the amount of the substance that's of interest, not how hard it presses against the ground. Likewise when someone measures body weight to assess health or attractiveness, it's how much matter is in the body that is concerned: being overweight would be just as unhealthy in a low-gravity environment. Body weight is measured in pounds-mass. In fact I can't think a "layman" use of pounds that are pounds-force (except if you consider torque in foot pounds and pressure in pounds per square inch as "layman" uses). It would end a lot of ambiguity if everybody quit using the word ''weight'' completely, replacing with "gravitational force" or "mass" as appropriate, but that's not likely to happen. Just as a government can't change the meaning of a word, neither can authors of physics textbooks change the meaning of word outside their field. User:Indefatigable 23:06, 15 Nov 2004 (UTC) ::::You see the facts pretty well, Bcrowell--you just appear to have some great difficulty understanding what you know. Yes, kilograms are indeed used for body weight throughout the world, including many hospitals in the United States. And they are indeed the proper SI units for this purpose, as NIST tells us in the external reference on the article page, at [http://physics.nist.gov/Pubs/SP811/sec08.html] :::::Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of". :::::Examples: the child's weight is 23 kg :::::: the briefcase weighs 6 kg :::::: Net wt. 227 g ::::It is your failure to understand that the pounds also used for this purpose in the United States, when used in either the medical sciences or in sports--the primary reasons we weigh ourselves--are the pounds legally defined as units of mass equal to 0.45359237 kg exactly. ::::Naturally, if you have been miseducated (as your students likely have been), told that pounds are not units of mass, you have to resort to such a faulty explanation. You imagine a discordance between the use of pounds for weight and the use of kilograms for weight which does not exist. Your major problem is a failure to understand the simple fact that "weight" is an ambiguous word, and it is compounded by your failure to understand the simple fact that pounds are and always have been primarily units of mass, not force. (The pound force is such a recent bastardization that it is uniquely identified by that name. There is no troy pound force, for example. There is no metric pound force.) ::::The Body Mass Index is also properly named. It is weight in kilograms divided by the square of height in meters. Or you often see it expressed in terms of weight in pounds and height in inches, with a conversion factor added. That conversion factor is always a constant (because of rounding, different people might use different values--but each author only uses one value). The exact number used in the Wikipedia article at the time I write this is 703.07, which is clearly too many digits to be used for pounds force without specifying a location--but one correct to that many digits for the pounds we do use. Nobody ever uses a variable dependent upon latitude and altitude in this context, which it would have to be if your mistaken belief that the pounds used for this purpose in the medical sciences are pounds force were true. ::::Note also that hospitals which have scales which can measure in either pounds or kilograms (it is often the same scale) do not use different methods to calibrate them for the measurement in pounds from the methods they use to calibrate them for the measurement in kilograms. It is a constant conversion factor between the two, whether it is accomplished by flipping the bar on a balance beam to get a different set of detents for the movable weights, or a constant conversion factor programmed into a microchip. ::::Note that the pennyweight, like the troy ounce or troy pound, is always a unit of mass. Similarly, the hundredweight (even for those who think hundred is written in digits as "112") and the stone (1/8 of a long hundredweight, still used for body weight in the U.K.), unlike the pounds on which they are based, have not spawned units of force of the same name. ::::Here's American Society for Testing and Materials, Standard for Metric Practice, E 380-79, ASTM 1979: "3.4.1.2 Considerable confusion exists in the use of the term weight as a quantity to mean either force or mass. In commercial and everyday use, the term weight nearly always means mass; thus, when one speaks of a person's weight, the quantity referred to is mass. . . . When the term is used, it is important to know whether mass or force is intended and to use SI units properly as described in 3.4.1.1, by using kilograms for mass or newtons for force." ::::BTW, it is also not true that kilograms are "undeniably units of mass, not weight" because the kilogram is usually a unit of mass when it is a unit of weight. But furthermore, changing your last word to "force" wouldn't matter either. The kilogram-force was a quite legitimate unit (also known by another name even, the "kilopond") before the introduction of SI in 1960. There were even coherent systems of units devised with the kilogram force as a base unit of force, with the derived unit of mass the kgf s^2/m, known by several different names such as slug (mass), TME from a German acronym, metric slug, or mug, because this wonderful invention recurred to several different people bound and determined to show that those using metric units can be every bit as silly as those using English units. We still see far too many vestiges of the use of these obsolete kilogram-force--but rarely for anything called "weight" in anybody's book, in any of the various different meanings of this ambiguous word. We see them used for thrust of jet and rocket engines, for tension of bicycle spokes even in the U.S.A., for pressure gauges in "kg/cm²", for torque wrenches in "meter-kilograms", etc. Nobody calls those forces weight. OTOH, the kilograms that are used for body weight of humans, or of other animals as well in fields such as zoology and veterinary medicine, and the kilograms that are used for "net weight" of anything are always units of mass, not force. ("Net weight" is not a physics term.) ::::The worst of it, however, Bcrowell, is that I suspect that you are not merely a physics teacher, but also a textbook author--of a textbook distributed primarily on the Internet, no less--who has spread his misconceptions in this field far beyond his own classroom. ::::User:Gene Nygaard 17:26, 6 Dec 2004 (UTC) -------- :::::I agree with Gene Nygaard here. The entire section added about force, weight, and mass confuses the issue, and is very poorly written. And of course the pound is only a unit of mass, and has been clearly defined as only a mass by all standards bodies and legislative definitions in all countries for well over a century. I'd recommend that the entire force, weight, and mass section be removed. It's meandering, wrong, and only comes from one person's very confused misconceptions. :::::In addition, I bristle at any article that says "but physicists/laymen/(insert other confused group) take it to mean something different" and then explain only their own confused, baseless misunderstandings. All such parts should be removed. People don't come to Wikipedia to find out about what some clueless people believe--they come to find out what's actually ''right''. The standards bodies (and even legislatures) that created these definitions well over a century ago clearly understood the difference between mass and weight, and differentiated them unambiguously. Too bad those who teach our kids don't. --User:Eliasen 08:22, 9 Jan 2005 (UTC) ::::::Sounds fine with me. User:Elf | User talk:Elf 18:48, 9 Jan 2005 (UTC) ::::::Eliasen, you know darned well that pounds are also units of force. Why are you trying to bury your head in the sand? ::::::Most of the information on the pound-force and its definitions and use belongs in the article of that name, but it needs to be mentioned here as well. ::::::It is very important to retain discussions involving the ambiguous word ''weight.'' There are far too many people who have gotten the mistaken notion that because a pound is a ''unit of weight'' it cannot be a ''unit of mass'' (a notion totally contrary to the fact that of all the pounds used throughout history, only one was also used as a ''unit of force'' to any significant extent). OTOH, we also have the confused people of Eliasen's class, insisting the opposite: that pounds are not ''units of force'' (even though from what I have seem, he or she appears not to understand the ambiguous nature of the word ''weight'' so the previously mentioned confusion would seem more probable). ::::::There are also far too many confused science professors in our colleges and universities, and high school teachers and the authors of some of the textbooks they use, filling the heads of students with the nonsense idea that they should measure "their weight" in newtons rather than kilograms or pounds. (And most everybody gets somewhat confused about this—and quite understandably so—failing to understand that the ''pounds'' used for this purpose in medicine and sports are units of mass, and that the ''pounds'' used for this purpose in many science textbooks, science museum exhibits, and other discussions of "your weight on other planets" are pound-force.) ::::::There are far too many professors and textbook authors who imagine themselves to be cheesemongers or purveyors of sugar, potatoes, bananas, or whatever, who do not understand that the kilograms used for that purpose—and, most important to this article, the pounds and ounces which appear right alongside them on labels in the United States—are units of mass, not units of force. I guess they must think that talking about the sale of cheese in a physics class can somehow magically change the rules—and they are the proper rules—governing its sale. (Of those who think the pounds are units of force, some think the kilograms are units of force as well, and others imagine some weird statement of measurements of two different quantities on the labels.) User:Gene Nygaard 13:40, 11 Jan 2005 (UTC) :::::::Let me be clear. The pound is a unit of mass. The pound-force is a unit of force, but that is ''not'' the pound. I have never said otherwise. Gene, do you have references by any standards body from any country in the past century that says that the pound is a force? If so, please produce it, otherwise, we should drop the whole force sections, which are in error. I don't want a confused colloquial usage, nor an industry shorthand, but an official standard by a national or international standards body. Say, since 1878 in the UK or 1893 in the U.S.? If so, we can maybe re-open this discussion, but it's been quite clear for a long, long time to all standards bodies (and even legal bodies, except for a minor confusion in Canada's legislative heading of the section of law that defines the pound.) Again, I have placed further references for a wide variety of countries and standards bodies http://futureboy.homeip.net/frinkdocs/faq.html#pound here. Do you dispute any of these countries' definitions? :::::::Gene, why do you say that people shouldn't measure their weight in newtons? That is, in fact, totally appropriate. Do you not agree that a newton is a force and that is indeed what is measured by almost all scales? If they're indicating their mass, it should be in kilograms or pounds. Weight is, obviously, not invariant under different accelerational frames, but newtons (or pounds-force) are quite appropriate to measure this varying quantity. I don't know where the confusion lies in your understanding. :::::::I agree that discussion of the pound-force should be in this article. In fact, I believe I put discussion of the pound-force in originally and linked to the pound-force article. It was simple, concise, and sufficient to show the difference. I will reiterate my opinion that any encyclopedia should focus unambiguously on ''correct'' usage, not confuse the issue with enumerating the endless permutations of incorrect colloquial usage. That isn't what an article on the pound should be about. :::::::I do believe that if people are confused about the difference between force/weight and mass, then that should be an entirely separate article, and not crammed into the article about the pound, otherwise it will be duplicated among all articles about mass or weight. This article needs cleanup badly. --User:Eliasen 08:29, 17 Jan 2005 (UTC) ::::::::I'll number my comments to correspond to your paragraphs 1-4. ::::::::1. Even if standards bodies had defined a "pound-force" that would not mean that pounds are not units of force. Any time you define something as a noun-adjective combination, it is logical and reasonable to expect that the adjective will sometimes be dropped. ::::::::However, since standards bodies haven't bothered to define pounds-force, even that is irrelevant. The existence of the pound as a unit of force, whether it is called just a pound, or by the old name "pound-weight" (which at least one old engineering textbook used to mean the geepound or slug, a unit of mass, instead), or the "pound-force" is determined by usage, not by standards bodies who have not acted. Various standards bodies have, of course, recognized the existence of pounds force. See, for example, the footnote 24 in NIST's appendix of conversion factors in SP811, giving a conditional definition of the pound-force. [http://physics.nist.gov/Pubs/SP811/footnotes.html#f24] ::::::::The main reason I brought that point up was to make sure that those reading this Talk page know what you know. You had written it like you were a dummy who didn't know pounds-force exist; whereas you merely intended to write it like a dummy who didn't know that they are called "pounds." ::::::::2. Show us some examples of the use of pounds-force for body weight (keeping in mind that you are the one claiming that pounds are not units of force if they are not identified as such). Better yet, show us all the examples you can find, from all around the world, of people using newtons rather than kilograms for body weight of humans, or of other animals as well in the veterinary or zoological sciences, for that matter. ::::::::"[M]easured on almost all scales?" So what happens when you get serious about your weight, and go to the doctor's office or the gym, and weigh yourself on one of those platform-type beam balances? Isn't that a better indication of what you want to measure, than a substitute considered acceptable in many homes because it is cheaply made? Furthermore, those cheap bathroom scales didn't even exist until 1937, well within the lifetime of many people living today. Those spring scales are no more accurate in measuring force than they are in measuring the mass at the location in which they are used. ::::::::How about those old scales that used to be seen in public places, where you could put in a penny and get your fortune told, as well as your Honest Weight: No Springs? ::::::::"[M]easured on almost all scales?" In a hospital, where they are concerned about not having discrepancies between the scales in different departments, or when someone is transferred to a different hospital, how are those scales calibrated? ::::::::Here are some of your "standards bodies" on this point. ASTM International, Standard for Metric Practice, E 380-79, ASTM 1979: ::::::::* 3.4.1.2 Considerable confusion exists in the use of the term weight as a quantity to mean either force or mass. In commercial and everyday use, the term weight nearly always means mass; thus, when one speaks of a person's weight, the quantity referred to is mass. ::::::::NIST [http://physics.nist.gov/Pubs/SP811/sec08.html#8.3 ''Guide for the Use of the International System of Units (SI),'' section 8.3] ::::::::*Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of." :::::::::Examples: the child's weight is 23 kg :::::::: 3. You don't even have any clear-cut, universal rules for the use of pounds force (or, for that matter, of English units in general), and not much from any standards organizations in the way of any guidance in their use, so even though I disagree with your philosophy here, it is irrelevant. :::::::: 4. The confusion most often seen in this regard, the confusion specifically mentioned by many standards organizations, is the confusion you seem to share (based on your "force/weight" and "mass" dichotomy, as well as your discussion about teachers in an earlier comment) with many (other?) science teachers—the failure to understand the simple fact that ''weight'' is an ambiguous word, one with several different meanings. Just remember this to help keep it straight in your mind: in the troy weight there are no ''troy-ounces-force'' and no ''troy-pounds-force''. :::::::: You've seen on this talk page, and on edits to the article itself, how this confusion about ''weight'' is the root cause of many peoples' beliefs that pounds cannot be units of mass. Even if it is discussed adequately (and relatively permanently, by Wikipedia standards) in another article, a good, strong summary accompanied with a link to that discussion is important in this article. ::::::::User:Gene Nygaard 15:02, 17 Jan 2005 (UTC) --------- :::McKay, I hope that little sister runs into better teachers. Soon. :::Maybe you could point her to the discussion on this page. :::User:Gene Nygaard 10:43, 8 Dec 2004 (UTC) ---------- ''...which is a dimensionless constant, defined as 32.17405 lb ft/(lbf s2) and approximately equal to the typical acceleration of gravity on Earth, in ft/s2.'' Is the use of the word ''dimensionless'' appropriate here? :It could probably be worded better (mea culpa), but it is indeed ''dimensionless'' though it is not ''unitless''. See dimensional analysis (a link to that in connection to the quoted statement might be helpful). As that says, a dimension is "the type of unit needed to express it"; for example, ''feet'' and ''meters'' have the same ''dimension'', something that in this context is usually called "length", often symbolized ''L''. Other dimensions involved here can be called "time" ''T'' and "mass" ''M'' (other "dimensions" could be chosen, for example force rather than mass, with the same end result). Let's do the dimensional analysis of those units: unit dimension lb ''M'' ft ''L'' lbf = 32 lb·ft/s² ''M'' ''L'' ''T''-2 s² ''T''2 and then combining them for overall dimensions, lb ft/(lbf s²) = lb ft lbf-1 s-2, so the dimensions are: (''M''1)(''L''1)(''M''-1 ''L''-1 ''T''+2)(''T''-2) =
''M''0 ''L''0 ''T''0 (i.e., dimensionless) :Now do the dimensional analysis of a formula involving this ''gc'' and you will see that the units as they are expressed in the quote above are indeed the correct units. Note the distinction made in the article between this conversion factor used in formulas, something called ''gc'', and the standard acceleration of gravity, ''gn'' = 32.174 ft/s², which has dimensions of acceleration, or ''L'' ''T''-2. User:Gene Nygaard 14:16, 27 Jan 2005 (UTC) ::You're right, of course. Thank you for the explanation. Having been brought up on SI I'm not used to these conversion numbers. Somehow, it feels a bit less dimensionless than some numbers, though. ;-) Possibly the wording could be improved by changing ''...and approximately equal to the typical acceleration...'' to ''...and numerically equal to the typical acceleration...''. I was confused by the units on the acceleration and assumed that the units on ''gc'' cancelled to the same.
Pound
-- User:Infrogmation 01:30, 5 Mar 2005 (UTC)
See other meanings of words starting from letter:
P
PA | PB | PC | PD | PE | PF | PG | PH | PI | PJ | PK | PL | PM | PN | PO | PR | PS | PT | PU | PW | PX | PY | PZ |Words begining with Pound:
Pound
Pound
Pound
Pound,_Ezra
Pound,_VA
Pound,_Virginia
Pound,_WI
Pound,_Wisconsin
Pound-force
Pound-force
Pound-force_per_square_inch
Pound-force_per_square_inch
Poundal
Poundbury
Poundbury,_England
Poundmaker
Poundon
Pounds
Poundsgate
Poundstretcher
Pounds_sterling
Pound_(currency)
Pound_(currency)
Pound_(disambiguation)
Pound_(sterling)
Pound_(town),_Marinette_County,_WI
Pound_(town),_Marinette_County,_Wisconsin
Pound_(town),_WI
Pound_(town),_Wisconsin
Pound_(village),_Marinette_County,_WI
Pound_(village),_Marinette_County,_Wisconsin
Pound_(village),_WI
Pound_(village),_Wisconsin
Pound_and_mil
Pound_and_mill
Pound_avoirdupois
Pound_cake
Pound_force
Pound_for_pound
Pound_Hill
Pound_Hill,_Crawley
Pound_House
Pound_it
Pound_key
Pound_mass
Pound_per_square_inch
Pound_Puppies
Pound_Ridge
Pound_Ridge,_New_York
Pound_Scots
Pound_sign
Pound_Sterling
Pound_Sterling
Pound_sterling
Pound_sterling
Pound_stirling
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