Wikipedia:Reference desk/Archives/Science/2016 March 10

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March 10

Why have two units, like Calories and Joules?

Why the redundancy? Wouldn't science be better off with just one? I understand that some duplicity is possible since difference geographical regions use different units. But, for example, in food packages, you have both side-by-side, although they can be converted unequivocally. --Scicurious (talk) 00:13, 10 March 2016 (UTC)

Some people use one unit, others use the other, so why not do the conversion for them ? StuRat (talk) 00:23, 10 March 2016 (UTC)

Some people use one unit, so, why not drop the other and impose this one on them?

And some people confuse cal and kcal. This is a further reason to drop cal/kcal. --Scicurious (talk) 00:33, 10 March 2016 (UTC)

Being off by a factor of 1000 means it's not a mistake people are likely to make. (If you eat a meal with 1000 kcals, it would be hard to imagine it has only 1, or a million.) StuRat (talk) 18:39, 10 March 2016 (UTC)

George Washington scolded Congress for failing to do anything about the chaotic weights and measures in the early US. Nothing ever changes. Jc3s5h (talk) 00:37, 10 March 2016 (UTC)

I went searching for sources to cite for that... I found that President Washington mentioned uniform weights and measures in the First Annual Message to Congress on the State of the Union (1790). This was notable enough to mention on NIST's Presidential Measurements Timeline. Nimur (talk) 04:44, 10 March 2016 (UTC)

If you made a food product for sale in the US, and dropped listing calories (if that was allowed), in favor of Joules, then your sales would drop off. That's reason enough not to do it. StuRat (talk) 00:38, 10 March 2016 (UTC)

It isn't allowed; the FDA mandates specify "calorie labelling". There are similar rules throughout layers and layers of federal, state, and local bureaucracies. The switch to another unit would have to be promulgated by hundreds of agencies, and they'd have to do it at the same time to avoid the nuisance of labelling in multiple units. It *could* be made to happen, I suppose, but there's have to be a good reason to go to all that trouble. So we don't even have to get to the point where "Joules" winds up confusing Americans. - Nunh-huh 05:00, 10 March 2016 (UTC)

The question is more about why sciences deal with two units that mean the same, than about practical aspects. But I see what you mean. It would only work if all implemented it at the same time. Scicurious (talk) 00:40, 10 March 2016 (UTC)

The calorie is a unit of heat, whereas the Joule is a unit of work. They both have units of energy, so there's an equivalence between them, but they were both natural for their own purposes at the time. --Trovatore (talk) 01:51, 10 March 2016 (UTC)

Why do you assume "sciences" deal with both units? In my field we're standardized on SI and would get a scolding from the editor if we submitted a paper using calories instead of joules. (Unfortunately we then have to translate when talking to members of the U.S. public, but such is life.) Shock Brigade Harvester Boris (talk) 05:00, 10 March 2016 (UTC)

Within the scientific community, isn't metric the standard? It's the general public that uses the customary system. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:50, 10 March 2016 (UTC)

See previous discussion about the use of "parsecs" and "lightyears" instead of kilometers (or gigameters or terameters) in astronomy. Scientists frequently use units that are neither SI nor even metric in their specific fields. However, if they needed to figure out the amount of the luminous flux of a star that reaches the earth from a distance of 100 lightyears - you can bet that the very first step in their calculations would be to convert 100 lightyears into meters. Furthermore, if the distance to the star was initially measured by the redshift method, the result of that calculation would probably have been expressed in meters and then converted to lightyears "for convenience". The point being that while there is a "convenience" factor to talking about lightyears (because in astronomy, time and distance are intimately related) - everyone knows that the SI system is the underlying stratum upon which everything is built. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

Calories and joules are both "metric". Calories are not SI. --Trovatore (talk) 08:03, 10 March 2016 (UTC)

The scientific community would use the joule. To the general public, "calorie" was already established, and "joule" sounds like "jewel" (or "Jewel" for that matter). ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:00, 10 March 2016 (UTC)

That's ridiculous - not everyone speaks English. Don't you think that "feet" and "inches" might get confused in other languages? The entire point of SI (System International) is that it transcends language barriers. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

Thanks, as always, for the unwarranted personal attack. Last I checked, this is the English Wikipedia. Whether other countries use calories or joules, I wouldn't know. But I note that caloría is used in Spanish, while the other unit is called julio, which normally means a month of the year. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:16, 10 March 2016 (UTC)

The question (which we are indeed answering in English) is about scientists...not "English-speaking scientists". Science is an international effort - cross-border (and cross-language) communication being a huge part of what most scientists have to do. I've never heard of anyone being confused between "Joules" and "Jewels" - it's pretty clear from context - and if your argument is that words that sound like other words shouldn't be used as units of measurement then I'd ask how many feet long my feet are and how many yards wide my yard is, how many pounds (force) do I pound my nails in with and...well, let's just get a second opinion about the second shall we? Your responses, are not well thought through - they are frequently incorrect. This time seems to be no different. SteveBaker (talk) 20:16, 10 March 2016 (UTC)

SI snobbery is unbecoming. All systems of units are essentially equally good. The conversions between them are trivial; you just have to use good integration testing to make sure they get done right. --Trovatore (talk) 06:22, 10 March 2016 (UTC)

No - not all units are equally good. Having a standard way to make big units and little units from standard ones, for example. I have no idea how many hogsheads there are in a firkin or teaspoonfulls there are in a cubic mile. But I know immediately how many micro-joules there are in a mega-joule or how many gram centimeters there are in a kilogram meter. Furthermore, the relationships between derived units like the joule and the underlying kg.m².s^-2 base unit is very clear. The BTU, on the other hand, requires you to know how much energy it takes to raise one pound of water through one degree Fahrenheit - which makes it really insanely difficult to use BTU's to calculate (say) the amount of rocket fuel you need to get to the moon where raising water temperatures are not involved. Then we get into the abbreviations of units being a mess...the confusion that some idiots introduced between the calorie and the kilocalorie is a terrible error - and SI units forbid that kind of crap - but what is the standard abbreviation for "a million BTUs"? It can be MBTU, MMBtu or mmBtu? All are allowed - but what about a million feet? So I'm sorry, but it's complete bullshit to say that no system of units is better than another. That's clearly, blindingly freaking obviously not true! So please stop propagating this untruth. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

I'm going to say THE TRUTH again. No set of units is better than any other.

You have no idea how many X are in a Y. So what? You can look it up. If it's something you do a lot, you'll learn it. --Trovatore (talk) 18:21, 10 March 2016 (UTC)

But why should I *have* to look it up? We can (and indeed have) designed a system that makes it entirely clear without having to look it up...or do pointless arithmetic to convert from one set of units to another. See my response below about trying to divide the width of a window into three parts using a stupid imperial tape measure. Even though I know the conversion - it's a pain in the butt to have to do it - and I'm very likely to make a mistake entirely BECAUSE of the stupid units problem. Sure you can memorize a bunch of random numbers and you can search online if you don't happen to remember how many grains are in a pound - then haul out a calculator to do it - but why on earth should you have to do such an incredibly stupid thing when there is a very well tried and tested system that the WHOLE of the rest of the world now uses? (er, except Liberia, and Myanmar). SteveBaker (talk) 20:43, 10 March 2016 (UTC)

Why should you have to? That's like saying, why should you have to have both a flat screwdriver and a Philips. You don't have to. But if you don't, you'll have trouble tightening screws of the other sort. Do you feel entitled to demand that people provide only the screws that fit your preferred screwdriver? --Trovatore (talk) 22:52, 10 March 2016 (UTC)

Sure. In my home workshop I have sets of flat, philips and torx screwdrivers - and about three dozen ball-tipped allen wrenches (metric and imperial) in my collection of tools (I also have some 'security by obscurity' robertson, triangular and other oddly shaped ones). I am also capable of operating in the realms of feet, yards and miles as well as SI units. However, when I'm building something new, I don't ever use screws with slotted heads - they strip too easily, and if the screwdriver slips out of the screw (which happens easily) it can gash your hand. I used to only buy philips-headed screws because, although they still strip - it's not as bad as flats, and the tool doesn't slip out of the screw. This has been the case for about the last 40 years - until just six months or so ago when DIY stores suddenly flooded with torx screws. Since Torx is vastly better than philips, I'm now actively "deprecating" my stock of philips screws and replacing with torx whenever possible. So, yeah - I can cope with flat-head screwdrivers - and with hogsheads, firkins, katals, pyrons, mireds and gilberts. But those are all obsolete. Yes, can still use them if I must - but no, I'm not going to use them for new work - especially if it's in the realms of engineering or science. But I have to recognize that while my car is made of torx bolts and screws - my laser cutters use allen and my house appears to use philips. I haven't seen a slotted screw in anything other than antique furniture for quite a while - and I like it that way! SteveBaker (talk) 14:51, 11 March 2016 (UTC)

The story of my 'conversion' to Torx (and problems related to that) are described in a medium.com story I wrote. SteveBaker (talk) 14:51, 11 March 2016 (UTC)

That's like saying that no system of mathematical notation is better than any other, or no programming language is better than any other. In reality, some are inherently less error-prone than others because humans don't work from formal specs; they rely to a large extent on cognitive abilities that haven't changed much in 100,000 years. And some are better because they are more widely supported/understood. -- BenRG (talk) 20:59, 10 March 2016 (UTC)

OK, look, I didn't literally mean that there were no system-specific advantages. That isn't the point at all. I assert that any inherent conveniences of any particular system are relatively minor. I also assert that trying to shame people into conformity with one preferred system just to avoid some potentially inconveniences is a bad thing. --Trovatore (talk) 22:52, 10 March 2016 (UTC)

Tell that to Mars Climate Orbiter or the Gimli Glider.... The sooner we get rid of non-SI units, the better. Fgf10 (talk) 08:07, 10 March 2016 (UTC)

Point of clarification: the Gimli Glider was caused by confusion due to Canada switching to metric. One could argue that it wouldn't have happened if Canada had stuck with imperial units. clpo13_(talk) 08:12, 10 March 2016 (UTC)

That's a point, but the more important point is that the testing was inadequate.

Same exact thing for the Mars Climate Orbiter. There's not a thing wrong with either set of units. There's not even anything necessarily wrong with using one set of units in one module, and a different set in another; it admittedly introduces more opportunities for error, but with correct testing procedures, you would find them. If you don't do the integration testing, there are all sorts of other errors you can miss that are not units-related. --Trovatore (talk) 08:31, 10 March 2016 (UTC)

Yes, I agree the Mars Climate Orbiter failed because they didn't test it properly - and because someone wasn't sufficiently clear in the specifications for interfaces between subsystems. It could equally have happened in an entirely metric environment if one subsystem used kilometers and another meters. However, we can find plenty of other cases - some potentially far more serious than either the MCO or the Gimli Glider incident. The US had for years used "grains" for weighing dry medicines...the abbreviation was 'g'. When imported bulk pharmacuticals from Europe started to turn up containers marked in grams ('g'), the US FDA insisted that they be re-labelled with 'gr' as the abbreviation for grams (a really, truly, classically stupid reaction to the problem!) Then grains stopped being commonly used and grams went back to being labelled 'g'...so there was ANOTHER change-over period while that was sorted out. What could possibly go wrong? Fortunately, one grain is 0.064 grams - so you're comparing grains to milligrams and there wasn't MUCH chance for an error in practice. But stupid things like that have the potential to cause tremendous harm. SteveBaker (talk) 21:28, 10 March 2016 (UTC)

The calorie was a base unit of thermal energy, the joule a derived unit of mechanical energy (kinetic, gravitational, electric). In the 19th century it was discovered that, using the proper conversion factors, mechanical energy and thermal energy could be converted into one another, keeping their sum constant. This meant that the joule could be applied to thermal energy too and made the calorie obsolete. It's no longer used, except for food. When talking about food, people for some strange reason stick to an irregular unit, even those people who have used SI units or their precursors for two centuries now in other fields. Maybe it's because there is a lot of pseudo-science in the food industry. In Europe, food is labelled in both kilocalories and kilojoules.

Not all scientists use SI. Some use cgs, which uses the erg as unit of energy. Both systems are equally good (and so is the FFF system), as both use conversion factors of 1 between combinations of base units and their derived units. 1 erg = 1 g·cm²/s², just as 1 joule = 1 kg·m²/s². This means there are no strange numerical factors in your formulas. The imperial or US customary systems don't: 1 btu ≠ 1 lb·ft²/s², 1 lbf ≠ 1 lb·ft/s² (using another unit of length instead of foot doesn't help). For the same reason the calorie is unwanted. PiusImpavidus (talk) 13:43, 10 March 2016 (UTC)

A it's heart, the original idea was that FFF is identical to SI except in the choice of the base units. It still uses milli and mega and the concept of having three fundamental base units (mass, length and time) that SI standardized. SI (as a concept) works just fine if you change the definition of a meter or a second (both have indeed changed since the inception of the system - the kilogram is about to go the same way). The point of SI is to define a system where we clearly understand that meters, kilograms and seconds are the fundamental things and derived units like joules are merely convenient shorthands that don't introduce new constants.

After the FFF system was first (jokingly) proposed, people have subverted it by talking about "BTU's per foot-fathom" (see our article on FFF) - which clearly puts FFF back into the realms of stupid antiquated systems where the derived units are not simply defined in terms of the base units. You can't tell how many BTU's are in a firkin fathom-squared per fortnight-squared (which would be the 'pure' FFF unit of energy) because you need to know the specific heat capacity of water and the definition of a foot and a degree farenheit in the FFF system to do that.

In the SI system, you know - without looking it up or memorizing weird constants that the number of joules in a kilogram meter-squared per second squared is exactly 1. You know that because the system defines derived units in terms of base units in a clear and unambiguous manner. How many joules is a pascal per cubic meter or a newton per square meter? I hardly ever need to do those conversions - but I know the answer is 1. How many BTU's is one atmosphere per cubic foot or one pound-force per square foot? Good luck with that! SteveBaker (talk) 15:13, 10 March 2016 (UTC)

What is at the heart of the misunderstanding of the SI-versus-imperial debate is that the pro-imperial people are only arguing that the foot, the pound and the second are just as good and useful as the meter, the kilogram and the second as "base units". I don't have any argument that the choice of base units is arbitrary in both SI and imperial - and one is as good as the other.

BUT that's not why SI is popular among scientists. It's for many more reasons than that:

1. Unit multipliers are the way that you abbreviate big and small numbers. SI defines a standard set of these: kilo, mega, giga, tera for big things. cent-, milli-, micro-, nano- for small things. There is no such thing as a kilo-foot in imperial - there could be - but there isn't. You have to convert feet into miles - which is a pain because you have to memorize the stupid conversion factor. Same deal with pounds, ounces and tons - these are all measures of mass - but they suck because there are more stupid conversion factors to memorize. If you're dealing with the more common units, you can maybe memorize quite a few of them - but the conversion from a grain to pound is not going to be tripping off the tongue if you don't use grains routinely.
2. Derived units. SI defines all 'convenience' units in terms of the base units. Joules, Pascals, Watts - all of these things are nothing more than abbreviations. A "joule" is merely a shorthand way of saying "kilogram meter-squared per second-squared". So you can have equations like F=m.a and so long as m and a are in standard units, F will come out in standard units too. In imperial units, 'force' will be in pounds-force (lbf) - and computing pounds-force from pounds (er pounds-mass I guess) and feet per second-squared requires you (bizarrely) to know the standard value for the force of gravity at the surface of planet Earth. Not so great if you're on the moon or something!
3. Standard abbreviations. What is the abbreviation for pounds-force? Well, you get to choose! lbf, lb_f or, if you prefer, just 'lb'...er...wait...run that by me again? The abbreviation for the standard unit of force is the same as the standard unit of mass? OMFG! What could *possibly* go wrong?!
4. Physics-based definitions for the base units: This is actually a fairly new thing for SI units - and we're not done with it yet. But the meter and the second are defined in terms of physically reproducible experiments. The kilogram still isn't - it's definition is "the mass of a specific lump of metal that's stored in a building just outside of Paris". The meter used to be defined as "the length of a specific lump of metal that's stored in that same building at such-and-such temperature" - but no longer, it's the distance that light travels in vacuum in some specific tiny fraction of a second (about 3 nanoseconds)...and the second is defined in terms of the amount of time it takes some specific atom to vibrate some ungodly number of times. This is important because the building with the standard meter in it could get hit by a meteor impact and we'd have no way to know how big a meter is anymore. The kilogram is going the same way - and probably it'll be redefined as the mass of some specific number of carbon atoms within the decade or so. How is the "foot" defined? Well, currently, it's defined as some exact fraction of a meter...which is pretty much an admission of defeat on this point! We long ago stopped defining the second as 1/(24x60x60) of the time it takes the Earth to make one revolution...which is just as well because that keeps changing. However, all of the funky old units are now defined in terms of the SI units...so SI has won that particular war and you 'imperial units' fans have to give up here!

So - the argument about SI versus imperial isn't about whether the foot is better than the meter. It's about having a consistent set of units with clear ways to make bigger and smaller versions, with clear derived units without wierd and changing "constants" like the gravity of the planet or the speed it revolves, with clear and rigorously defined abbreviations. Once we fix the kilogram, we'll be able to make instruments to measure things without having to calibrate them against copies of copies of copies of the lump of metal in Paris. We have atomic clocks that keep perfect time because by definition they are perfect. That's why scientists use SI - it's nothing to do with the convenience (or otherwise) of the three base units.

My one significant problem with SI is that kilogram doesn't have an un-prefixed name. We should really have gone with something like the french word "Grave" (which means "one kilogram") so that we wouldn't have a base unit with a prefix. There is pressure to make that change - but it probably won't happen. SteveBaker (talk) 15:43, 10 March 2016 (UTC)

SteveBaker (talk) 15:43, 10 March 2016 (UTC)

My hat off to you sir, hardly seen it argued better before. Fgf10 (talk) 15:55, 10 March 2016 (UTC)

@SteveBaker: I had thought a kilogram was "the mass of 1 liter of pure water, i.e. a cubical volume of water 10cm on a side (1000 cubic cm) at standard temperature and pressure." I've always thought it was a damn convenient way to convert quickly between volume and mass for a liquid. Weights and volume conversions in cooking become a snap too (most liquids you cook with — raw eggs, milk, alcohol, even oils — are near enough in density that 1kg=1L is a good approximation. Imperial units have a similar convenience: 1 fluid ounce of water is approximately equal to 1 ounce in weight, so a pint of water is about 1 pound. ~Amatulić (talk) 05:42, 12 March 2016 (UTC)

They say, "a pint's a pound the world around", but the last time I was over there, it was only about 90p. Which may give you some idea how long it's been.... --Trovatore (talk) 06:05, 12 March 2016 (UTC)

The physics-based definitions are important, but not by any means unique to SI. Most customary units have been redefined in terms of the SI ones anyway, so they are implicitly just as physics-based. The "admission of defeat" thing is silly; you're still using (almost exactly) the unit you were using before.

The rest of it is all essentially about minor conveniences. Sure, things are more systematic, and there are times that that saves you ten seconds or so of looking stuff up. The ten seconds don't really accumulate; if you're going to do something repeatedly, you will build the conversion factor into whatever you're doing. --Trovatore (talk) 18:29, 10 March 2016 (UTC)

Powers of 10 are handy for scientists, but they are not very good human-oriented measurements. There's nothing inherently better about the meter vs. the yard, or the kilometer vs. the mile. And decimeters are both too large and too small, and centimeters are too small, for humans to relate two. The foot and the inch are much more relatable. That's part of the reason the metric system remains mostly a curiosity in America, outside of the scientific community. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:21, 10 March 2016 (UTC)

Powers of 10 are NOT the point. Powers of 2 or 12 would be just as useful - arguably more so. I already said that meters versus yards isn't important. But "decimeters are too large or small"...???!!! What for? If I need to measure things that fit into the bed of my 2'x4' (60cm x 120cm) laser cutter - approximately - then feet are far too big for any kind of useful approximation and inches are too small. A decimeter is actually the perfect size for that (although, personally, I'd think in centimeters). That feet and inches are "more relatable" is utter BS. When putting up a curtain rod last night, I needed to divide the width of the window in three. My wife handed me her "sewing" tape measure that has only feet, inches and some random-looking number of tick-marks between the inches. Is that tenths? Eighths? Who knows? OK...look carefully - ah - it's 16ths. OK so I have 8 feet, 7 inches and 11 sixteenths of an inch. Great...what's a third of that? I can't do (8x12+7+11/16)/3 in my head - certainly not while balancing on the top of a ladder! Oh crap - go off to my workshop, grab a metric/imperial tape measure, OK 263.4 cm. I can do 2634/3 in my head - it's 87.8 cm. Hooray.

It's just what you grew up with. I went to school in the UK right on the cusp of the metric introduction - so I was taught both systems. I "think" in metric and imperial with utter ease and have no more problem thinking in either set of units. Neither is more convenient as absolute distances - I don't "prefer" an inch or a centimeter - but I *do* prefer the SI system. The only reason it's not popular in the US is because it's not popular in the US.

You can't deny the value of the four points I described above - you just can't. You're down to pathetic arguments about the "relatability" of ONE of the base units - and you can't even back that up with anything more than a gut feel. If the metric base units were hard to relate to - don't you think there would be pressure in (say) France or Germany to use feet and inches? I don't see that. All I see is pressure in the USA to convert the last major country on the planet from an antiquated system to something a little more modern. The fix for your "relatablity" issue is to teach children the metric system in school as their PRIMARY units of measurement. Within a generation, the pressure to dump the old fashioned units would be overwhelming. SteveBaker (talk) 20:09, 10 March 2016 (UTC)

Your vulgar personal attacks defeat any points you may raise. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:16, 10 March 2016 (UTC)

So you've run out of counter-arguments? OK. SteveBaker (talk) 20:47, 10 March 2016 (UTC)

No, I stand by what I said. What you said has become irrelevant. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:49, 10 March 2016 (UTC)

Huh! That's an interesting debating style. I'm not sure "You upset me, so you must be wrong" is one of the ways to convince people...but it's your call. SteveBaker (talk) 21:06, 10 March 2016 (UTC)

Vulgarity doesn't upset me. It merely diminishes the one who uses it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:13, 10 March 2016 (UTC)

I don't want to get into this discussion too much but when people talk about "powers of" are they referring to the Base (exponentiation)? If so, I think the key point which often seems to be missed is that decimal is the system almost universally used nowadays with a few limited exceptions like in computing science. Other systems were used in the past but we've almost universally settled on 10, perhaps because we humans have 10 fingers or toes. Easier divisions may mean duodecimal (12) would be a better base and as SB I think has said binary (2) also has advantages. But as much as we can imagine how much better it would be if we humans generally had 12 fingers or we'd stuck with some other way of counting or whatever but sadly that didn't happen.

In other words, like it or not, decimal has become the natural system to most humans regardless of any possible flaws or better alternatives. This is the case even for nearly all users of imperial/US customary users. When something is 10 decimal or 130 decimal inches, pretty much everyone writes it as 10 inches or 130 inches, not a inches or aa inches. Maybe the later will be written as 10 feet 10 inches or 3 yards, 1 foot, 10 inches but never a feet a inches. The fact that we don't really have a symbol other than the letters of the English/latin alphabet for any bases beyond 10 is a sure sign of this. And as SB has said, I'm guessing even for many normal users it took longer to convert the 130 decimal inches into yards, feet and inches then it ever should a similar metric unit conversion.

If people using imperial/customary units were actually using a different base universally then it may make more sense, but they're not. In fact as SB has said and the yard-foot-inch example has shown, it's not like the bases used are consistent in the units they use anyway, so they can't.

Nil Einne (talk) 21:14, 10 March 2016 (UTC)

If metric was so wonderful, we would have adopted it already. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:17, 10 March 2016 (UTC)

But, um, we have? Nil Einne (talk) 21:29, 10 March 2016 (UTC)

Where appropriate. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:35, 10 March 2016 (UTC)

Which is nearly everywhere. As mentioned above and below, I use SI nearly everywhere. The only places I may not use SI are time (I do use the second, but also the minute, hour day etc) and temperature (I normally use celsius rather than Kelvin which while making now difference in terms of magnitude, is different in terms of absolute values) and for units in space (I do use the lightyear etc on occasion as it's a useful unit). Oh and I normally use PSI for tyres because that tends to be what the meters and data book displays by default and I don't do any calculations. (Most meters can actuall change to kPA but the unit used here is actually fairly arbitary so I don't really give a damn. I wouldn't likely use PSI were I actually calculating something.) If I was a pilot I may be forced to use feet but I'm not and I'm pretty sure your not a pilot either so it's largely a moot issue. Since I'm not a pilot, when I do fly I tend to view the SI flight information units. And frankly, the main reason why pilots still use feet seems to have more to do with tradition and the risks of switching over. If I were navigating or in charge of a ship I may use nautical miles but I'm not and again I suspect you're not either. (Although this, along with time and celsius as temperature is perhaps one of the few units where there's a reason to keep using it.) I do see any reason to use inches, yards, ounces, pounds, Fahrenheit etc etc and there are probably over a billion people like me, definitely more than those using inches, yards etc. (Although possibly even more do have some usage of other units.) In other words, where appropriate is "nearly all the time". Nil Einne (talk) 17:53, 12 March 2016 (UTC)

You're choosing to use it for your own reasons, but generally it's non-standard in America. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:05, 12 March 2016 (UTC)

P.S. It's perhaps worth remembering that even for people like me who almost never has any need to use non SI for most units (except when reading something written by someone who doesn't use SI and the limited non SI) and frankly only have a vague idea on the conversion for even some more basic units like inches, pounds etc (and I'm pretty sure I'm better than my younger brother who's doing a PhD in engineering); it's not like we don't deal with the problem of inconsistent bases.

Time is one of the few areas which hasn't properly changed and for various reasons probably isn't likely to change any time soon. As SB has said, when I'm going between other units it's trivial (worst case you make an order of magnitude mistake which you'd normally pick up). Working out how long 518 seconds let alone 572782 seconds is annoying and I at least have okay mental maths. Sure I can pull up a calculator on my computer in a few seconds if needed but this doesn't mean it isn't still annoying. In fact since I sometimes specify stuff in milliseconds when scripting for various reasons, even within the units it's obvious how much simpler it is.

Nil Einne (talk) 21:29, 10 March 2016 (UTC)

Yes, the world needs a wristwatch with a decasecond and kilosecond hand! Sadly, the rotation rate of the Earth isn't some handy power-of-ten seconds - but it was never a good choice as a basis for time because it doesn't spin or orbit at a sufficiently uniform rate and we have to fritz around with leap-seconds. Certainly for fractions of a second, you're forced into SI because there don't seem to be imperial units of time less than a second. As a programmer of video game graphics, ruled by a 16.667 millisecond frame time, a millisecond starts to seem like a long time, and microseconds are a useful unit. Most of the time, an inch is close enough to 25mm and a foot is more or less 30cm...the rest don't generally impinge much on my daily life. When I need precision, as a user of Linux (or Cygwin under Windows or BSD under OS-X), I install the wonderous command-line "units" program - which can happily tell me how many oersted furlongs there are in a gilbert (20,116.8!) - and 'bc' which is a command-line calculator that can provide 100 digit precision and work in base 37 if you want it to. I have a similar program to 'units' on my phone - but most of the time, Google does the job easier (it doesn't do oersted-furlongs though). But for most work, doing things approximately in your head is strongly desirable - and for that, it's hard to beat SI. SteveBaker (talk) 15:15, 11 March 2016 (UTC)

I think the reason why Calories (note distinction from "calories", even though they are almost written "calorieinch

s"!) hang on with food is pretty obvious: they're not practically convertible with anything else. A few biodiesel geeks excepted, you don't burn food in your furnace, and you sure as hell can't make it using kilogram weights and a high cliff (excepting if they land on something with tasty meat). So you're asking the whole dieting world to change its units to something they don't know, sentence themselves to a lifetime of multiplying any figure they ever learned in their life by 4 point something in order to compare it to what they're reading on the label today to see if this is a higher- or lower-calorie equivalent, all based on a theoretical correspondence with a unit of heat that they by and large wouldn't know how to do calculations with even if there were any relevant calculations they needed to make. This reform is not going to happen until the days when the consumers are shackled to tracking robot devices that tell them what people of their class and health status are allowed to eat or not, and when it happens it will be an internal update in the software that the consumers don't have the right to reverse engineer even if they had the inclination or mental capability to do so. Wnt (talk) 13:30, 11 March 2016 (UTC)

There are two problems with the calorie - as used for foods and diet plans. Firstly is the horrible mixup between calories and kilo-calories - and second is the problem of what exactly is being measured, and how. The problem is to know how much energy an average human being will extract from one serving of some food or other, you have to either submit some poor experimental subject to having their poop and pee and sweat and breath measured while sitting in a tank of warm water - or you have to kinda guess by measuring their CO2 production. That's a horrendous ordeal to go through for every change in the shape and size of a gummy-bear or every one of the (allegedly) 57 flavors of Cambell soup. So what they actually do is to use a 'bomb calorimeter' and burn the food to ashes to get it's "true" energy content and make assumptions about the efficiency of a typical human gut.

So it's not just that the numbers aren't convertible into other units - it's that we're not even measuring the thing we're claiming that the number represents.

There are few other units that suffer from that kind of issue - perceptual sound and light levels are another - the pain scale - that kind of thing.

Since the science behind what is being measured is so flakey - it's perhaps just as well that we define a special unit and use it (more or less) only for that one purpose. Hoping that when someone decides to build a car that runs on gummy-bears (oh, trust me, there are nut-jobs out there who are thinking about it as we speak!), they don't try to use the calorie number on the packaging label.

I do recall at least one case of confusion caused by the calorie versus the kilo-calorie - and that was when someone claimed that drinking cold beer cause your body to burn more energy in maintaining body temperature than the beer itself contained - so beer must be a good diet food. As expected, the label on the beer bottle said something like "200 calories" and the math done on the bodily cooling was done with joules and converted to proper SI calories and came up with the answer 3,600 calories to warm a bottle of beer to body heat. So on the face of it, drinking beer will be an extremely effective diet!

SteveBaker (talk) 15:33, 11 March 2016 (UTC)

It see arbitrary what unit of energy something is expressed in. I like kilowatt-hours. Edison (talk) 02:42, 13 March 2016 (UTC)

Do Americans still buy their petrol (gasolene) in gallons? There are 20 fluid ounces in a pint, so a pint of water weighs 1lb 4oz. Then there are eight pints in a gallon - a gallon of water weighs ten pounds. The US gallon is a little smaller, but if you divide it into eight I think the weight of water would be more than one pound. Metric is not very well organised - for example the base unit of area is (unsurprisingly) the are, although everyone deals in hectares. And let's not forget that imperial units are conveniently related to parts of the body - a foot is, well, a foot, and when I was working in the market, if I didn't have my yardstick handy I could measure a length of cloth from my outstretched hand to my nose. The stock market doesn't bother with decimals - it's more convenient to quote prices in halves, quarters, eighths and sixteenths. An important feature is the mid - price - the average of what traders are buying and selling at. So if they're buying at 32 and selling at 33 the mid - price is 32 1/2. Simple. 5.150.93.133 (talk) 12:16, 13 March 2016 (UTC)

Yes, Americans still use US gallons for gasoline (and water, milk, paint, pretty much any bulk liquid). In the US there are 16 fluid ounces in a pint, Eight pints in a gallon. The old british system was yet more confusing with 16 ounces in a pound and 20 fluid ounces in a pint. SteveBaker (talk) 04:00, 14 March 2016 (UTC)

Hence the old expression, "A pint's a pound the world around." Our American world, anyway. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:27, 14 March 2016 (UTC)

Clinical engineering

How difficult is it to become a hospital clinical engineer if you have a degree and work experience in civil engineering but plan on doing a postgraduate degree in biomedical engineering? 2A02:C7D:B907:6D00:801E:EA0C:2468:72D9 (talk) 05:13, 10 March 2016 (UTC)

See Clinical engineering. If you have an inventive mind and you like engineering, then this role could be right for you. You will need excellent technical knowledge and also good communication skills to work with patients and understand their needs. To get into this job you will need a relevant degree in physics or engineering. To work in the English NHS you will then need to apply for the postgraduate NHS Scientist Training Programme. - See more at: [1] AllBestFaith (talk) 15:20, 11 March 2016 (UTC)

Field engineers

Which types of engineers work in the field and away from desks/cubicles the most? 2A02:C7D:B907:6D00:801E:EA0C:2468:72D9 (talk) 05:24, 10 March 2016 (UTC)

I'd go with Civil_engineer. 196.213.35.146 (talk) 06:21, 10 March 2016 (UTC)

Why is that? And any sub-disciplines of civils in particular? 82.132.237.203 (talk) 07:45, 10 March 2016 (UTC)

Military engineering has most distance form desks/cubicles id say. But its hard to tell because Engeneers typically become specialists in their job and thus its much more dependent on what job you take then what branch of engeneering you pick at start. --Kharon (talk) 08:38, 10 March 2016 (UTC)

When it comes to things like dams, bridges, roads, etc. the engineer has to spend a lot of time on site. Sure he's given the contractor the specs but he has to make sure they are implemented properly. New dams are not likely to be built anywhere near your office. You spend a lot of time in the field and often this is in the boonies - further than is practical to commute - so you may even live on site for weeks/months at a time. 196.213.35.146 (talk) 12:25, 10 March 2016 (UTC)

Here is an example in the news. The engineers are based in Italy and the project is in Iraq. http://news.sky.com/story/1657170/mosul-dam-humanitarian-catastrophe-warning 196.213.35.146 (talk) 12:30, 10 March 2016 (UTC)

The Field engineers that spend most of their working lives in the field must be the Farm “farm laborers”. They engineer fields, turn the soil, transplant cauliflower when the rain and sleet is flying horizontal, ensure Monsanto earns a fortunes by spaying Roundup here there and everywhere, harvests the wheat all night under the harvest moon. In fall (autumn), they become arborists by cutting hedges and relaying them. Their hydrogeological skill are employed when clearing drainage ditches. Living on a farm they probably don't have access to the internet, so in their free time they are probably out in the garden tending to their lettuces, rhubarb, tomatoes and kohlrabi. Then perhaps get into a bit of Environmental Bioengineering by turning over their compost heaps from time to time. Compared to a graduates fresh out of agricultural collage they shine brighter than the midday sun and they are out in it -come all weathers – in the field. To appreciate their many skills, one one has to communcate with them. In the UK that means knowing a little bit of Polish, in the US of America a working knowledge of Hispanic and Google Translate on the mobile helps. Remember, with out their skills, will would starve.Where as, a civil engineer gets upset when his green wellies get muddy.--Aspro (talk) 20:31, 10 March 2016 (UTC)

No way! A company calls a "field" a defined area of customers. An engineer who maintains projects and problems occuring at the customer site might also be called a field engineer.[2] This is an engineer who travels. --Hans Haase (有问题吗) 12:52, 12 March 2016 (UTC)

Electric utilities send mechanical, civil and electrical engineers into "the field" at some point in their careers. They check field conditions, draw up plans for additions or modifications, and create "as-built" drawings. The electrical engineers might test relays or test transformers and circuit breakers. At other points in their careers they might stick to the office, creating general plans and budgets for system expansion.Edison (talk) 02:48, 13 March 2016 (UTC)

Energy content of water and carbon dioxide

I know that water and carbon dioxide are both energy-poor compounds, the end products of the oxidation of high-energy, organic compounds. Water and carbon dioxide do not burn. I was intrigued, however, when I read that carbon dioxide can react with water to produce carbonic acid, an exothermic reaction. I read on a website (I think it was by Harvard) that carbonic acid is lower in free energy than carbon dioxide, I suppose the way that carbon dioxide is lower in free energy than oil. I asked my biology teacher about this last part, and she said that of the two, water has more energy, but seeing the Harvard website gave me a different impression. I have also found Wikipedia's article, water-fueled car, and it is plain to see that water has a very low energy content. However, you can burn water; you just can't do it in oxygen. Water burns in fluorine, suggesting it must contain some chemical energy. So I was wondering: which has more energy - water or carbon dioxide? I was also wondering what else reacts with water (besides fluorine). Is there any other way to obtain chemical energy from water (using a different electron acceptor)? Finally, I was wondering if anyone could tell me more about the dissolution of carbon dioxide in water to form carbonic acid. I have references that specifically say this is an exothermic reaction. Does that mean that if I dissolve some carbon dioxide in water, the temperature of the water will increase (assuming I don't use dry ice, which is very cold and would cool off the water)? Will the temperature of the water drop when the carbonic acid breaks down into carbon dioxide and water again?162.40.215.36 (talk) 05:39, 10 March 2016 (UTC)

The reaction of water and fluorine doesn't necessarily mean that the water gave off energy, it could also be the fluorine. Note that pure sodium (not sodium chloride/table salt) reacts violently with water, but, again, the energy released may well come from the sodium. A more rigorous way to think about it is that the reaction products have less binding energy than the reactants. StuRat (talk) 06:46, 10 March 2016 (UTC)

Yeah - this is a common idea among the water-fuelled car crazies. The reactant with the abundance of energy in it is what we call "the fuel". So if you add fluorine or sodium into the water, the "fuel" is the fluorine or the sodium - not the water. So, yeah - you could make a sodium-fuelled car (which happened to need a tankful of water to make it work) - but that's no different than an old-style steam car that uses coal or wood as the fuel and needs a tankful water to make it work. The problem with both of those things is that we don't have cheap, abundant (and definitely not renewable) sources of elemental fluorine or sodium. You'd have to put a LOT of energy into the system to make either of those products - and that would by far exceed the energy you'd get back from reacting it with water. Sodium is extracted from salt by electrolysis, and fluorine from potassium fluoride, also by electrolysis. So rather than going the roundabout route of using the electricity to produce one of those lethally dangerous chemicals, then transporting and storing them under horrific hazmat conditions - why not just use the electricity to charge the batteries of an electric car?

The carbonic acid thing is somewhat more interesting. I'm not a chemist - but you should note that very little CO2 combines with the water - even under pressure. So you'd need a truly, insanely, vast amount of water and CO2 to produce any significant amounts of net energy - and with such huge quantities of reactants, the temperature rise would likely be too small to measure, let alone exploit as a source of power. This is clearly a non-starter. Note that so little of it forms that it wasn't until 1993 that anyone was able to show that carbonic acid even exists as a pure compound - and that claim wasn't confirmed until 2011!

Both water and CO2 are common byproducts because they are the lowest energy state of the chemistry that produced them. It's like burning some logs in a fireplace and then expecting to extract heat by doing chemistry with the resulting cold ashes the next day. Even if there is the tiniest amount of energy to be had via the carbonic acid route, for any practical use, you need a much denser fuel. If you wanted to run a vehicle on water and compressed CO2, you'd get more propulsion by using the pressure of the CO2 to drive a pneumatic motor and build a small over-shot waterwheel to drive the wheels as the water flows out of a gigantic water tank on the roof! (And in that case, the water and CO2 aren't fuels, just ways of storing gravitational or pneumatic energy.)

SteveBaker (talk) 14:18, 10 March 2016 (UTC)

I don't disagree with the logic, but it actually is possible to extract some heat by doing chemistry with cold ashes. Wood ash is highly alkaline -- many "folk" technologies relied on dissolving wood ash in water to get a rather potent base. Looie496 (talk) 15:23, 10 March 2016 (UTC)

To put some numbers here, I calculate the heat of reaction for the H2O (l) + CO2 (g) -> H2CO3 reaction to be -20.3 kJ/mol. That's exothermic, but still 2 orders of magnitude lower than a typical combustion reaction (propane is ~2,000 kJ/mol). The other problem is that the equilibrium constant for this reaction is small (our article says 1.7×10⁻³). So only 0.17% of the carbon dioxide that you put into the water actually reacts to form carbonic acid, while the remaining 99.83% either dissolves in the water or just sits there. COULD you run a car this way? I doubt that the energy that you would get out of it wouldn't even move the mass of equipment, water, and CO2 required to run it, much less move a car effectively. shoy (reactions) 14:57, 10 March 2016 (UTC)

For the last bits, see Carbonic_acid#Chemical_equilibrium and perhaps Ocean_acidification. SemanticMantis (talk) 15:18, 10 March 2016 (UTC)

Hi, me again (different IP address). Some great answers here. I was under the impression that fluorine was a stronger oxidizer than oxygen and so water really was the electron donor (fuel) in this reaction. Is that not true? To be fair, though, I also read that it takes energy to produce the fluorine, so you can't use it to fuel a car anyway. I really wasn't interested in water-fueled cars, just curious if water has any chemical energy in it? It doesn't have any at all? Just gravitational energy? Also, I really appreciate your answering my question about the dissolution of carbon dioxide in water. I especially liked the bit about confirming the existence of carbonic acid. Could someone provide a reference for the heat of reaction? I thought it released more energy.174.131.45.84 (talk) 15:42, 10 March 2016 (UTC)

You can't talk about chemical energy that way. There's a reason chemists use change in enthalpy, change in free energy, etc, when they report the results or models. It's because that's what you can measure. Even in the case of gravitational binding energy, this is also just a change in energy (specifically the difference between "current state" and "exploded to infinity"). Any time the reactants in a chemical reaction have more energy than their products, this change is called a release of chemical energy. There is still energy inside a water molecule in the form of electrical, nuclear, and gravitational bonds (. You can define water molecules as having zero "chemical" energy but that would be totally arbitrary, and not to mention the energy inside a water molecule changes with its environment. Someguy1221 (talk) 02:56, 11 March 2016 (UTC)

See Le_Chatelier's_principle and here [3]. There's also a nice animated graphic in this [4] related discussion. SemanticMantis (talk) 16:01, 10 March 2016 (UTC)

I couldn't find a direct reference for the heat of reaction for the formation reaction, it was calculated using Hf data from Perry's Chemical Engineers' Handbook. shoy (reactions) 16:30, 10 March 2016 (UTC)

As far as your use of the term "fuel", that's a bit misleading. While we don't normally think about the oxygen in the air as fuel, it really is every bit as much fuel for the reaction as whatever gets oxidized. It's just semantics that has us not call it that. (Kind of like we don't normally call people animals, although we obviously are, from a scientific POV.) StuRat (talk) 18:36, 10 March 2016 (UTC)

Distinct types within a species

I am trying to find out if there is a term for what might be called "intra-species morphological differentiation"; in other words, distinct forms or types within a species such as worker vs. soldier ants, etc. (?) --2600:1004:B002:C399:C9B7:34:47D9:C78D (talk) 18:10, 10 March 2016 (UTC)

Perhaps you mean Polymorphism (biology) (or "castes" for ants specifically). Sean.hoyland - talk 18:31, 10 March 2016 (UTC)

The term "breed" is used for domesticated animals, though it's apparently kind of loosely defined. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:06, 10 March 2016 (UTC)

What it's called can depend a little bit about where it comes from, and whose sense of the words you are following, how much of a stickler you are, etc. Fortunately I have a very reliable source hand from which I will quote - The Insect Societies by E.O. Wilson, p. 136:

"Polymorphism is defined in a special sense in the social insects as the coexistence of two or more functionally different castes within the same sex. The castes must be stable during one or more instars. ... Most commonly it denotes noncontinuous genetic variation within a population, and as such it is especially well entrenched in the literature of genetics. Consequently Mayr (1963) has proposed the alternate term polyphenism for nongenetic variation of the sort seen in the caste systems of social insects."

Now, it is important to note that many castes are actually not genetically controlled. Certainly not in the bumblembees, nor in queen determination of honeybees, but there is genetic control in the Melipona [5] and in many other clades. Understanding the interplay between genetic and environmental cues in caste determination in specific species and groups remains an active area of research, regularly appearing in Nature [6] and new results appearing as recently as last year [7]. So, if you are referring to social insects, "caste" is a fine word used by experts in the field. Polymorphism is more general, but do watch out for polyphenism, and the fact that you don't want to necessarily imply genetic control when it isn't there. SemanticMantis (talk) 19:14, 10 March 2016 (UTC)

Hmmm, interesting distinctions not clearly explained in articles Polymorphism (biology) and Polyphenism (Too bad I have "retired" from WP editing) -2600:1004:B002:C399:C9B7:34:47D9:C78D (talk) 19:59, 10 March 2016 (UTC)

I think it's ok. The first sentence of polyphenism clearly says arising from a single genotype, and lists social insect castes as a prominent example. The third paragraph of polymorhism explains that sometimes it means a genetic basis and sometimes it doesn't. I have shoe-horned a linked "polyphenism" into the intro, that should help a little. SemanticMantis (talk) 20:17, 10 March 2016 (UTC)

Ring modulation

Is ring modulation just a way of saying that a circuit implements convolution? I think that's what the article is saying but it's not totally clear to me. For the purposes of this question, I don't care about the fact that a real-world heterodyne of this sort may fail at accomplishing mathematically perfect convolution. Thanks, SemanticMantis (talk) 18:54, 10 March 2016 (UTC)

Yes that is what the article says. But real life heterodyne, eg guitar tuning, is additive, not multiplicative, in the time domain. The spectral content of that result is the same as the sum of the input spectra signals, the time domain waveform looks as though it is the average frequency, with an amplitude envelope at the difference in frequency, for equal amplitude signals. Greglocock (talk) 19:56, 10 March 2016 (UTC)

Thanks! I had also missed some of the back-and-forth between time and frequency domains. So ring modulation is multiplicative on the time domain, and convolutional on the frequency domain, which is sort of backward from the way I first came across these issues (that time convolution is simply multiplication on the frequency domain). SemanticMantis (talk) 20:20, 10 March 2016 (UTC)

Heterodyne means different frequencies (literally same power). Whereas homodyne means same frequency. Amplitude Modulation can be achieved by adding two signals and then passing the resultant through a nonlinear process. Also observe the Beat frequency page. Greg is correct though obscure.--31.109.183.147 (talk) 01:33, 11 March 2016 (UTC)

See also single-sideband modulation. --Hans Haase (有问题吗) 12:56, 11 March 2016 (UTC)