Weight vs. Mass: I know their NOT the same, but cannot comprehend why

[Monkeh]

I suppose this is why when interplanetary with the Kerbal engineer redux mod the TWR's get so screwy

Pretty sure this single nuke engine isn't producing 1300 twr...

[rkman]

Kilograms are a measure of both mass and weight. Weight kilograms are equal to mass kilograms multiplied by the local gravity.

Except that nobody ever uses "weight kilograms" and "mass kilograms". And because "1 kg = 9.81 kg" would be confusing, science and engineering use kilograms and Newtons instead.

[Diche Bach]

I appreciate the merits of metric and I try to use it whenever possible. Certainly in the papers I have published where units of measurement are involved I've used metric.

But in defense of the old Imperial system . . . I think for length at least, feet and inches are more 'intuitive' for the 'hands on' contexts where non-scientists (but including craftsman, workmen, and just plain homeowners) tend to use them. Compare:

My ceilings are 8ft ceilings vs. 2.438 meters ceilings

[Bunsen]

Except that nobody ever uses "weight kilograms" and "mass kilograms". And because "1 kg = 9.81 kg" would be confusing, science and engineering use kilograms and Newtons instead.

I have seen instances, disturbingly many in fact, of the perverse unit called the "kilogram force" or kgf. Naturally, it is the weight experienced by a kilogram of mass at standard gravity, but I'm not sure whether it's the product of intentional trolling or if some deranged minds were simply jealous of the confusion and silliness enjoyed by users of the Imperial system. I think anyone who commits such a sin should be forced to spend a week doing thermal analysis in slugs, millifurlongs, BTUs, and microfortnights.

[Holo]

Except that nobody ever uses "weight kilograms" and "mass kilograms". And because "1 kg = 9.81 kg" would be confusing, science and engineering use kilograms and Newtons instead.

When you step on the scales, you are using weight kilograms. When you read how heavy a plane is? Weight kilograms.

[Anton P. Nym]

When you step on the scales, you are using weight kilograms. When you read how heavy a plane is? Weight kilograms.

Not really.... that's really a shortcut for "has the same weight as a mass of x kilograms at the Earth's surface". Any time we start seriously talking about weight as a force instead of a mass* in SI we do talk in terms of Newtons.

-- Steve

* colloquially they do get confused, a lot; a '70s kids educational show Eureka! used that confusion to good effect by proposing that while diet and exercise helped reduce your mass, going into orbit was a much better weight reduction plan than giving up donuts.

[Xeldrak]

Over here we would simply place the ceiling at 2.4 meters

Well, to be hones, if you grow up with metric system it's just as intuitive to you. I'm from a craftsman family - it's just a question of familiarization.

@Holo Not, the scale tell you your mass. But the scale only works on Earth - for some reason no manufacturer cares to mention that. On Moon the scale would give you a nonesensical number - neither your weigt, nor your mass.

Edited September 2, 2013 by Xeldrak

[Randox]

I appreciate the merits of metric and I try to use it whenever possible. Certainly in the papers I have published where units of measurement are involved I've used metric.

But in defense of the old Imperial system . . . I think for length at least, feet and inches are more 'intuitive' for the 'hands on' contexts where non-scientists (but including craftsman, workmen, and just plain homeowners) tend to use them. Compare:

My ceilings are 8ft ceilings vs. 2.438 meters ceilings

Only because houses/buildings are built to the imperial standard. The metric equivalent to a foot would really be the decimetre (10 cm, 30.24 inches, or ~0.33 feet). Instead of an 8 ft ceiling, you could probably go with 24 decimetre ceiling (just under an inch shorter), and instead of 18 inch spacing on the wall studs, perhaps 4.5 decimetre spacing (less than a cm off if I am doing all my conversions right). Imperial is quite convenient, but metric would give you pretty similar sizing, particularly because the decimetre is almost a perfect third of a foot (it's a little bit less past the second decimal). That said, imperial does work quite well, since the inch divides into useful sizes (down the eighth's), but not being in base 10 is a royal pain.

For the whole mass/weight thing, I find it easiest to keep in mind the units. Kg is weight, and the I'm going to say the idea of Kilogram-weight is literally going backwards seeing as metric already has the Newton. The Newton has units of KG*m/s^2, the units of force (mass times acceleration) which is what weight is. The force an object exerts because of gravity acting on it's mass. Looking at the actual units of Newtons, "kilogram meters per second squared", you can see why we just use N. Usually you only start expanding the units for the sake of conversions, or solving particular problems, where it's more convenient to have everything in terms of the base units, like mass and length and time (m, kg, s) all multiplying and dividing.

[Stochasty]

Pounds, btw, are a unit of mass. When talking about force, you'll invariably see lbf (pounds-force) used, which are each the amount of force gravity exerts on one pound of mass at Earth's sea level = 32.174049 lb*ft/s^2

I always see it used the other way: pounds as a measure of thrust, pound-feet for torque, etc. The only time I ever see anyone explicitly use pound-mass (or, for that matter, even distinguish between the two) is when I see an engineer or a scientist forced to work in the Imperial system.

As an aside, despite being originally from the US I now think almost exclusively in metric; it's just so much easier to do so. About the only Imperial units I still use are inches (centimeters are a little too small, and decimeters too large, to make for easy eyeball guesstimation of short distances); however, I think meters rather than feet for large distances. This makes for interesting conversions between the two; I've gotten reasonably good at dividing by factors of 39. Also, because I haven't done much driving outside of the US I haven't internalized kilometers per hour yet. Miles per hour of meters per second are fine, but kilometers per hour require me to mentally convert.

[lajoswinkler]

Kilograms are a measure of both mass and weight. Weight kilograms are equal to mass kilograms multiplied by the local gravity.

Weight kilograms? What deranged man came with that idea? I've never heard of it before. Kilograms were invented as a unit of mass, and any "weight kilograms" would be a backward step to an incredible mess.

kilograms - mass

newtons - weight (force)

Plain and simple.

I appreciate the merits of metric and I try to use it whenever possible. Certainly in the papers I have published where units of measurement are involved I've used metric.

But in defense of the old Imperial system . . . I think for length at least, feet and inches are more 'intuitive' for the 'hands on' contexts where non-scientists (but including craftsman, workmen, and just plain homeowners) tend to use them. Compare:

My ceilings are 8ft ceilings vs. 2.438 meters ceilings

That's an issue only in the regions where ceilings are 2.438 metres high. My ceiling is at 2.7 m though modern apartments can use 2.7 or even 3 metres. Offices often use 3.4 or 3.5 metres.

What confuses me with metric is the lack of decimal approach. Why would anyone think of dividing length into 12 pieces? Why not 10? We've got 10 fingers. It's intuitive from a prehistoric approach, and became incredibly useful when things like logarithms were developed. You just shift the decimal point. It lets you explore and compare stuff from quarks to galaxy clusters.

As an aside, despite being originally from the US I now think almost exclusively in metric; it's just so much easier to do so. About the only Imperial units I still use are inches (centimeters are a little too small, and decimeters too large, to make for easy eyeball guesstimation of short distances); however, I think meters rather than feet for large distances. This makes for interesting conversions between the two; I've gotten reasonably good at dividing by factors of 39. Also, because I haven't done much driving outside of the US I haven't internalized kilometers per hour yet. Miles per hour of meters per second are fine, but kilometers per hour require me to mentally convert.

It takes a few years, I guess, but people can shift to it.

Let me tell you from a standpoint of someone who lives on the European continent - decimetres aren't units you'll hear in the everyday conversation. We use millimetres, centimetres, metres and kilometres. Occasionally micrometres, when someone bumps in talking about precision drilling, microbes or wavelengths.

You'll never hear decametres or hectometres. Decagrammes and hecrolitres (not a true SI unit, but derived from it) yes.

Edited September 2, 2013 by lajoswinkler

[Ralathon]

That's an issue only in the regions where ceilings are 2.438 metres high. My ceiling is at 2.7 m though modern apartments can use 2.7 or even 3 metres. Offices often use 3.4 or 3.5 metres.

What confuses me with metric is the lack of decimal approach. Why would anyone think of dividing length into 12 pieces? Why not 10? We've got 10 fingers. It's intuitive from a prehistoric approach, and became incredibly useful when things like logarithms were developed. You just shift the decimal point. It lets you explore and compare stuff from quarks to galaxy clusters.

base 12 is actually much more useful than base 10. You know how the table of 2 and the table of 5 are really easy because they keep repeating the same pattern? For base 12 you have that for the table of 2, 3, 4 and 6. And the universe really doesn't care what numerical system we use, the laws of mathematics apply whether you use base 10 or binary. The problem about the imperial system is that it isn't self consistent like the metric system is. 1 kilometer is 1000 meter and 1000 millimeter is 1 meter, but a mile is 1760 yards and 36 inches is 1 yard.

Also, base 12 can be very intuitive. Ancient Egyptians used base 12. You have 12 finger bones in your 4 fingers, and you can keep track with your thumb.

[Mr Shifty]

About the only Imperial units I still use are inches (centimeters are a little too small, and decimeters too large, to make for easy eyeball guesstimation of short distances); however, I think meters rather than feet for large distances. This makes for interesting conversions between the two; I've gotten reasonably good at dividing by factors of 39. Also, because I haven't done much driving outside of the US I haven't internalized kilometers per hour yet. Miles per hour of meters per second are fine, but kilometers per hour require me to mentally convert.

Yeah, I do electronics design, and there are lots of parts still specified in inches. (Thous or mils, which are thousandsth of an inch, are very common in precision machining and sort of a metricization of the Imperial unit.) I actually estimate in yards (or more precisely: (American) football fields) for longer distances, which are approximately the same as meters, so an easy conversion. Interesting to note that 1 m/s is a little over 2 miles-per-hour, which is an easier in-your-head conversion than to kph.

[lajoswinkler]

base 12 is actually much more useful than base 10. You know how the table of 2 and the table of 5 are really easy because they keep repeating the same pattern? For base 12 you have that for the table of 2, 3, 4 and 6. And the universe really doesn't care what numerical system we use, the laws of mathematics apply whether you use base 10 or binary. The problem about the imperial system is that it isn't self consistent like the metric system is. 1 kilometer is 1000 meter and 1000 millimeter is 1 meter, but a mile is 1760 yards and 36 inches is 1 yard.

Also, base 12 can be very intuitive. Ancient Egyptians used base 12. You have 12 finger bones in your 4 fingers, and you can keep track with your thumb.

Of course, whatever the base you use, the math is the same. I'm aware of that. It's the consistency I like. Most people who are raised on metric don't really appreciate it because they take it for granted.

12 finger bones in 4 fingers, thumb excluded? Yeah, I'm sure people first noticed that, instead of the fact they have 10 of them on their hands.

I'd understand base 5 (one hand) or even base 20 (fingers+toes). But 12... just no. I'm talking from an late evolutionary standpoint.

Yeah, I do electronics design, and there are lots of parts still specified in inches. (Thous or mils, which are thousandsth of an inch, are very common in precision machining and sort of a metricization of the Imperial unit.) I actually estimate in yards (or more precisely: (American) football fields) for longer distances, which are approximately the same as meters, so an easy conversion. Interesting to note that 1 m/s is a little over 2 miles-per-hour, which is an easier in-your-head conversion than to kph.

Sometimes I wish m/s would be used instead of km/h (kph is a faulty unit, it's the same backward issue as weight-kilogramme) because m/s is closer to our motion.

I still normally use km/h because I'm accustomed to it, and the conversion (factor 3.6) does not amuse me.

Edited September 2, 2013 by lajoswinkler

[rkman]

I have seen instances, disturbingly many in fact, of the perverse unit called the "kilogram force" or kgf.

Also "pound-force". As far as i know it is/was used in rocketry... http://en.wikipedia.org/wiki/Kilogram-force http://en.wikipedia.org/wiki/Apollo_Command/Service_Module Service Propulsion System: "The 20,500-pound-force (91,000 N) SPS engine was used to place the Apollo spacecraft into and out of lunar orbit..."

When you step on the scales, you are using weight kilograms. When you read how heavy a plane is? Weight kilograms.

Nobody calls it "weight kilograms" nor "mass kilograms". Without that distinction the difference between one and the other is not apparent, so you would end up with 1kg=9.81kg.

[rkman]

12 finger bones in 4 fingers, thumb excluded? Yeah, I'm sure people first noticed that, instead of the fact they have 10 of them on their hands.

Merchandize in one hand, with the other hand counting to twelve using the thumb. Quite convenient. http://en.wikipedia.org/wiki/Dozen

[Diche Bach]

Absolute zero and absolute hot boggle my mind.

I also have a hard time understanding how "length" is a true ratio scale that has a true absolute zero point. Temperature, sure something can exist and have zero temperature (though getting to that point has proven to be rather challenging it seems); also seems to be that reality can have zero electrical charge or mass (photons).

But length, duration and 'energy' I'm not clear on how anything can truly exemplify an absolute zero point for any of these dimensions.

Something with zero length doesn't exist does it? Or perhaps it is safe to say that photons or "a" photon has zero length?

Has there ever been anything in existence that was "zero duration?"

Lastly 'energy;' if something exists then it must either have mass or energy or both, right?

[lajoswinkler]

Merchandize in one hand, with the other hand counting to twelve using the thumb. Quite convenient. http://en.wikipedia.org/wiki/Dozen

True, but people learned to count before they invented economy. Maybe 10 was the first base used, but somehow some societies diverged from it...

Absolute zero and absolute hot boggle my mind.

I also have a hard time understanding how "length" is a true ratio scale that has a true absolute zero point. Temperature, sure something can exist and have zero temperature (though getting to that point has proven to be rather challenging it seems); also seems to be that reality can have zero electrical charge or mass (photons).

But length, duration and 'energy' I'm not clear on how anything can truly exemplify an absolute zero point for any of these dimensions.

Something with zero length doesn't exist does it? Or perhaps it is safe to say that photons or "a" photon has zero length?

Has there ever been anything in existence that was "zero duration?"

Lastly 'energy;' if something exists then it must either have mass or energy or both, right?

Why is that boggling your mind?

At 0 K every motion except the fundamental (quantum crap, let's not go into it, let's keep it simple) stops. Absolute hot is not what bugs me. It's the notion that there is no upper limit to temperature.

Realistic zero length is perhaps impossible, if Planck length exists. Something like voxels with Planck length base. It's a hypothesis. We don't know. It would solve one paradox.

Planck time also. As for energy, though we're sure about it.

Everything that exists has either a mass or energy, though I'm pretty sure everything that exists has both, however small. Photons have one type of mass, which helps them push against stuff (solar sail). Zero rest mass, though. (controversial subject, this rest and relativistic mass, let's keep it simple)

[rkman]

True, but people learned to count before they invented economy. Maybe 10 was the first base used, but somehow some societies diverged from it...

Source? I'm not so sure: put two people together, chances are each has something that the other wants. Next thing you know they are trading. They wouldn't have a stock market but it counts as economy in my book. And people have been living together ever since there are people. For all i know 12-base is older than 10-base, the latter came with the arabic number system (10 symbols including zero) that most of the world has adopted (in Europe during the late middle ages).

Absolute hot is not what bugs me. It's the notion that there is no upper limit to temperature.

I'm not sure what you mean there. Do you mean that "absolute hot" is the notion that there is no upper limit to temperature, or do you mean that the notion of no upper limit to temperature bugs you? In any case: "Absolute hot is a concept of temperature that postulates the existence of a highest attainable temperature of matter. ... Current cosmological models postulate that the highest possible temperature is the Planck temperature," - wiki http://en.wikipedia.org/wiki/Absolute_hot Edited September 2, 2013 by rkman

[Diche Bach]

Why is that boggling your mind?

Probably because my mind is fairly simple

However, what boggles my mind about it is this. My fairly simple training in statistics has led me to understand that, the mathematical inferences one can legitimately make (particularly statistical inference) are constrained by the nature of the numbers involved.

As a simple example, it would be invalid to use a nominal (categorical) or ordinal scale measure to calculate a square or a square-root, operations that are integral to many forms of hypothesis testing. There are of course nonparametric statistical algorithms, but those tend to offer more limited options.

At least historically, there seems to have been some debate about whether it is safe to treat interval scale measures like Celsius temperature as if it were actually a ratio scale in this case. So I have for example, heard people complain that "You can't do a linear regression on anything that is not absolutely, positively a ratio-scale variable." For example, these issues are captured here in the wiki page on Levels of measurement.

Interval scale

The interval type allows for the degree of difference between items, but not the ratio between them. Examples include temperature with the Celsius scale, which has an arbitrarily-defined zero point (the freezing point of a particular substance under particular conditions), and date when measured from an arbitrary epoch (such as AD). Ratios are not allowed since 20°C cannot be said to be "twice as hot" as 10°C, nor can multiplication/division be carried out between any two dates directly. However, ratios of differences can be expressed; for example, one difference can be twice another. Interval type variables are sometimes also called "scaled variables", but the formal mathematical term is an affine space (in this case an affine line). . . .

Central tendency and statistical dispersion

The mode, median, and arithmetic mean are allowed to measure central tendency of interval variables, while measures of statistical dispersion include range and standard deviation. Since one cannot divide, one cannot define measures that require a ratio, such as the studentized range or the coefficient of variation. More subtly, while one can define moments about the origin, only central moments are meaningful, since the choice of origin is arbitrary. One can define standardized moments, since ratios of differences are meaningful, but one cannot define the coefficient of variation, since the mean is a moment about the origin, unlike the standard deviation, which is (the square root of) a central moment.

Ratio scale

The ratio type takes its name from the fact that measurement is the estimation of the ratio between a magnitude of a continuous quantity and a unit magnitude of the same kind (Michell, 1997, 1999). A ratio scale possesses a meaningful (unique and non-arbitrary) zero value. Most measurement in the physical sciences and engineering is done on ratio scales. Examples include mass, length, duration, plane angle, energy and electric charge. Ratios are allowed because having a non-arbitrary zero point makes it meaningful to say, for example, that one object has "twice the length" of another. Very informally, many ratio scales can be described as specifying "how much" of something (i.e. an amount or magnitude) or "how many" (a count). The Kelvin temperature scale is a ratio scale because it has a unique, non-arbitrary zero point called absolute zero. The zero point of the Celsius scale is at 273.15 kelvins, so Celsius is not a ratio scale.

Central tendency and statistical dispersion

The geometric mean and the harmonic mean are allowed to measure the central tendency, in addition to the mode, median, and arithmetic mean. The studentized range and the coefficient of variation are allowed to measure statistical dispersion. All statistical measures are allowed because all necessary mathematical operations are defined for the ratio scale.

So here is where it boggles my mind: you've just pointed out that there may actually be nothing like "zero length" in reality. Zero temperature, zero electrical charge, sure, sure, those exist.

But zero length? Zero 'time?' Zero energy?

What if those are in fact "impossible?" Does that mean that our measures of these things are really nothing but interval scale measures and mathematical operations that assume they are in fact true ratio scales are actually erroneous?

I'm fairly primitive when it comes to maths, and what little physical science I have is just sort of 'absorbed' over the years. So forgive me if I'm just being silly.

Actually it has been a while since I've picked up a statistics textbook, and I do recall some of my more accomplished colleagues poo-pahing the argument that variables must be ratio scaled to do things like least-squares linear regression. I seem to recall "ratio scale" being declared as one of the operative assumptions of least-squares linear regression in my older textbooks, but I'm not seeing it mentioned as such in what appears to be a pretty nice and up to date wiki page on the topic.

Edited September 2, 2013 by Diche Bach

[lajoswinkler]

Source? I'm not so sure: put two people together, chances are each has something that the other wants. Next thing you know they are trading. They wouldn't have a stock market but it counts as economy in my book. And people have been living together ever since there are people. For all i know 12-base is older than 10-base, the latter came with the arabic number system (10 symbols including zero) that most of the world has adopted (in Europe during the late middle ages). I'm not sure what you mean there. Do you mean that "absolute hot" is the notion that there is no upper limit to temperature, or do you mean that the notion of no upper limit to temperature bugs you? In any case: "Absolute hot is a concept of temperature that postulates the existence of a highest attainable temperature of matter. ... Current cosmological models postulate that the highest possible temperature is the Planck temperature," - wiki http://en.wikipedia.org/wiki/Absolute_hot

I've picked that up during my highschool sociology and psychology classes, but you might be right on that. Even if you're right, I don't see why base 10 wouldn't be the easiest. There are ten highly visible appenages on your frontal manipulatory tools (hands, lol). They just beg for attention.

The notion that there might be infinitely hot bugs me, and so far, that's the accepted idea. There is no limit to the energy a particle can have. I don't know... I just find it weird.

Diche Bach, whenever my brain starts derping with such problems, it quickly tries to save itself by postulating quanta of whatever there is. I imagine space like a voxel grid, with each voxel of Planck length dimensions and unimportant shape. There is no "between" and there is no "travelling across the voxel". Something either is or isn't exactly at some voxel. Then I'm fine and can get back to whatever I was doing.

Edited September 2, 2013 by lajoswinkler

[CrazyFizik]

Absolute zero and absolute hot boggle my mind.

I also have a hard time understanding how "length" is a true ratio scale that has a true absolute zero point. Temperature, sure something can exist and have zero temperature (though getting to that point has proven to be rather challenging it seems); also seems to be that reality can have zero electrical charge or mass (photons).

But length, duration and 'energy' I'm not clear on how anything can truly exemplify an absolute zero point for any of these dimensions.

Something with zero length doesn't exist does it? Or perhaps it is safe to say that photons or "a" photon has zero length?

Has there ever been anything in existence that was "zero duration?"

Lastly 'energy;' if something exists then it must either have mass or energy or both, right?

Absolute zero is unattainable. Temperature of 0K impossible to obtain any way. This is the third law of thermodynamics.

Photons can exist only in the moving at speed of light. At this speed the rest mass (invariant mass) of the photon approaches zero. It is derived from the Lorentz transformations (special theory of relativity). Also there is a particle having a negative and imaginary rest mass.

But that does not mean that a photon can not have mass. For example the light beam is deflected by massive celestial objects.

The fact is that there are several varieties of types of mass. There are inertial mass, passive gravitational mass, active gravitational mass, invariant mass. In classical physics, they are equal, but in modern physics are different concepts. And in different frames of reference mass of the same object will be different.

[Jackissimus]

Coming a bit late into the discussion, but anyway:

In my work I often perform installations of scientific instruments which are either American-made, Japan-made or German-made. I have to say that I like the German instruments the most. The Japanese have their horrible "Japanglish", which makes the manuals nearly unreadable, but the imperial units sometimes really boggle my mind. Like the first time I installed an antivibration table with the air pressure measured in psi. Pounds per square inch? Really? How do I convert that into bars? My toolbox is basically twice the size because I need to carry the metric tools and imperial tools. And what's with the weird ratios on the allen keys? How is it easier for anyone to have an allen key of the size 5/32 inch or 7/64 inch?

That said I have to say that the little inconsistencies in SI units also tick me off sometimes, being the perfectionist that I am. Why is the kilogram the base unit of mass? Shouldn't it be simply the gram without the prefix? Why don't we use megameters or gigameters (well, except KSP)? Why don't we use gigagrams instead of tons? Shouldn't this be the more logical system?

I also think we shouldn't be using degrees in angle measurement anymore, it's just completely arbitrary to have 360 degrees, 60 minutes, 60 seconds. We should be using radians instead, it's just a matter of getting used to it and it makes the math simpler.

Regarding Dichebach's point: if you grow up in metric, you don't think of imperial. I have no concept of the ceiling being 12feet high, I have to convert to meters. I never measured in feet and when I try to use my feet to measure something, I quickly realize that my foot is smaller than 30cm. Usually when I try to guess the height of a ceiling, I use me as a quick mental measuring stick, because I am about 180cm high.

Edited September 3, 2013 by Jackissimus

[lajoswinkler]

Jackissimus, the weird "Japanglish" is called Engrish. Use Google Images... I promise you'll laugh your ass off.

Pounds per square inch... one of the most irritant units I've ever encountered. I remember once having to convert data written on a gas tank in the era before WWW. It gave me a headache. That should be converted to kilograms per square metres, and then into newtons per square metres, which are pascals, and then dividing by 101325. Correct me if I'm wrong.

Bars and pascals aren't SI units, though. Pascals are derived, and bars are like mmHg, kind of obsolete.

I don't know why they've chosen kilogramme for the base unit instead of gramme. I presume it's because it existed before the things became official. It has something to do with gramme-centimetre-second system used before that. Gramme and centimetre are too small units for most applications, so kilogramme-metre-second was used. I don't know.

The other stuff you're complaining about aren't inconsistencies in SI. Megametre and gigametre are SI units, but you'll rarely encounter them because of the same reason you won't hear about terametre or petametre. Nobody cares.

Tonnes do not belong to SI. They're derived from SI, but they're allowed for usage. If you want, you can use gigagrammes. There's no law stoping you from doing that.

Radians would be more convenient for some applications, but navigation would be difficult, and degrees are so incredibly stuck into the society it would be nearly impossible to replace them. It's a worse case than imperial units in some countries. One thing that makes me vomit when it comes to navigation is the usage of knots. What the hell... :S

[Diche Bach]

Ah, conversions from one unit of measure to another . . . such a 'small' thing relatively speaking but with such capacity to cause a bad, bad day; even to the tune of $655,200,000

The Mars Climate Orbiter (formerly the Mars Surveyor '98 Orbiter) was a 338 kilogram (750 lb) robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander. However, on September 23, 1999, communication with the spacecraft was lost as the spacecraft went into orbital insertion, due to ground based computer software which produced output in non-SI units of pound-seconds (lbf×s) instead of the metric units of newton-seconds (N×s) specified in the contract between NASA and Lockheed. The spacecraft encountered Mars at an improperly low altitude, causing it to incorrectly enter the upper atmosphere and disintegrate.[1][2]

[Jackissimus]

Jackissimus, the weird "Japanglish" is called Engrish. Use Google Images... I promise you'll laugh your ass off.

Oh maaaan ... Random outbursts of laughter in my office ... I am trying to hold it in now, I hope my boss doesn't notice...

Some gems (sorry for OT):

Pounds per square inch... one of the most irritant units I've ever encountered. I remember once having to convert data written on a gas tank in the era before WWW. It gave me a headache. That should be converted to kilograms per square metres, and then into newtons per square metres, which are pascals, and then dividing by 101325. Correct me if I'm wrong.

Bars and pascals aren't SI units, though. Pascals are derived, and bars are like mmHg, kind of obsolete.

Pascals are derived, so they are recommended, and all derived units are actually really easy to derive, there are never any conversion constants to remember (with the sole exception of Celsius, which is Kelvin + 273). Bars are actually non-SI units, you are right, but they are exactly 100 000Pa, so they are sort of pegged to Pascals. We don't usually use pascals to talk about gas pressure, only the weathermen use them for this (they usually say "we will have 1013 hectopascals today", how is it your country?). Everyone uses bars here, but they could just as easily be using Pascals, the real pressure unit.

Edited September 3, 2013 by Jackissimus