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Why the USA does not use the metric system

  1. Aug 2, 2015 #1


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  2. jcsd
  3. Aug 2, 2015 #2
    Lame, we need to go metric!
  4. Aug 2, 2015 #3


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    We must have been editing my post simultaneously. I originally went on autopilot and used HTML 'a href' tags for the link because I had just been editing some of my own web pages. Then I realized what I had done and tried to fix it, but it came out differently from what I intended! Your version works, so I'll leave it alone. :-p
  5. Aug 2, 2015 #4


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    These types of stories just serve as Click-Bait for CNN. :mad:

    The metric system gets plenty of workout in the US in science and technology, especially manufacturing. Just about every car and truck on the road now is designed using the metric system, not only those models made by the Big Three domestic car makers, but also all the European and Asian brands which have set up manufacturing facilities in the US, a lot of their output which is exported back into their home markets.

    I'm an engineer by profession, so while I do most of my work in the USCS system, I do have to understand SI as well. Even though I was not raised to think metric, I believe knowing two systems has been beneficial to me in my work because I can check a metric result to see if it is reasonable.

    On the pages here at PF, I have seen students raised wholly in the metric system who sometimes calculate fantastically wrong results in their native measurement system and not realize what has occurred. For whatever reason, they're not sure if a cubic meter is bigger or smaller than a litre, and the welter of different SI, MKS, and CGS units can often give the unwary fits.

    Face it, measurement systems are conventions, where a group of people agree that this unit of measurement (the foot, the meter, the pound, the kilogram, etc.) will be the standard used in trade or science. No one convention, all such being human constructs, will be perfect or will satisfy all who use it.
  6. Aug 2, 2015 #5


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    ... and, you've had to develop the mental agility to use both. Hear-hear.
  7. Aug 2, 2015 #6
    The big question is, 'is the US gallon a superior measure of volume to the British Imperial gallon?'
    Never mind them weird foreign liters and stuff.


    I once heard (can't recall source), that an early Mars probe missed the planet because of a part designed in one system of units was mistakenly made with a different system.
    Dunno if that's true.
    Last edited: Aug 2, 2015
  8. Aug 2, 2015 #7


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    IMO, it's just different.

    The Imp. gallon was sized so that 1 gallon of fresh water at 62 F weighed exactly 10 pounds. This makes it a snap to figure of the weight of so many Imp. gallons of water, and if you know the specific gravity of a different liquid, you can quickly figure its weight as well.


    Apparently, the US gallon is a holdover unit from the reign of Queen Anne (d. 1714), when it was used for measuring wine.

    Both gallons are divided into quarts, pints, and so many fluid ounces, such that the UK pint is about 1.2 times the size of a US pint. There are 128 fluid ounces in a US gallon, but 160 ounces in 1 Imp. gallon.
  9. Aug 2, 2015 #8
    What! .. decimalisation!
    What's wrong with dozens, scores, and bales and reams!
  10. Aug 2, 2015 #9
    You're probably thinking of the Mars Climate Orbiter. Great fodder for illustrating the importance of labeling units to students.

    Being adept at working in different unit systems is certainly a skill worth having. It seems like there are still many units in use that are very field specific. The bolt (fabric length unit) and brix (sugar concentration) come to mind. I wonder how many different unit standards there are today. Apparently toward the end of the 18th century in France there were more than 250,000 different units in use because each town had their own system (source) - hence the push for standardization.
  11. Aug 2, 2015 #10
    Yes that would be it, but I was wrong about it missing Mars.
    It was meant to go into orbit but instead it crashed into the atmosphere and the problem wasn't to do with the manufacture of a part, it was to do with software that used a different measurement system to the hardware.
  12. Aug 2, 2015 #11
    Britons use Imperial in every day life - pints, miles, feet, inches, stones. Most people my age or older still mentally convert (double it and add thirty) centigrade to fahrenheit - 40 is chilly, 50 is cool, 60 is warm 70 is perfect, 80 is hot, 90 is a heat wave coming on. 23°C - not so much of a mental picture there. I have no mental picture of what somebody 167cm tall and 74kg looks like. But 5'10 and 9 stone - I can see that. I can imagine a hike up a mountain 4000ft. 1300 meters not so much.

    But, for most calculations, Imperial (and the strange units) are just way too clumsy.
  13. Aug 2, 2015 #12
    Hmm, That would be quite a noticeably thin person but not extemely thin, could probably benefit from eating more and daily exercise.
  14. Aug 2, 2015 #13


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    There's still plenty of those. There's 8 stone to a hundredweight (cwt), and 20 cwts. to the ton (2240 lbs), which is a couple of percent larger than a metric ton (1000 kg).

    The world still prices some commodities using non-metric units, like oil is priced at so many US dollars for a barrel of 42 US gallons. You can't actually buy a physical container with a capacity of 42 gallons any more, as most steel drums measure 55 US gallons.



    Beer is also sold by the barrel, but these barrels measure 31 gallons in the US.
  15. Aug 3, 2015 #14
    I've spent my career using non-metric units (what are they called, "Imperial." "US," "customary"??) in other words: feet, pounds, gallons and so on. I don't understand the fuss people make over which system to use. My approach? Use the system your co-workers use.

    On a whim I checked the pipe standards, to compare the ANSI sizes to the DIN sizes. Using 6-inch pipe as an example, the ANSI pipe is 6.625 inch OD. The DIN 150mm pipe OD 168.3 mm. The ANSI schedule 80 pipe wall thickness is 0.432 inch; the DIN pipe has 11.0 mm wall. Now for the surprise: the two pipes are identical - 6.625 inches is 168.3 mm; and 0.432 inches is 11.0 mm. So, are we not using metric pipe? Or are the Europeans not using ANSI pipe? Actually I was surprised; I had always assumed that the DIN sizes would be maddeningly different. Cooler heads obviously prevailed when the "new" standard was created...

    If there is anything I really like about SI, it is the separation between mass & weight, to avoid the endless confusion we have here in the US (pounds mass, pounds force, do I divide by 32.2 here or not...). For the SI aficionados: anyone report their body weight in newtons? Or are you all still using kg-force? To me, that's just leaving the best part off.
  16. Aug 3, 2015 #15
    Mass in Newtons?
  17. Aug 3, 2015 #16
    Weight in kilograms??
  18. Aug 3, 2015 #17

    Vanadium 50

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    How many scruples are in a hogshead again?
  19. Aug 3, 2015 #18
  20. Aug 3, 2015 #19
    11 imperial gallons is almost exactly 50 liters in the metric system.
    Have I discovered a new universal constant?
  21. Aug 3, 2015 #20


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    Or how many ergs are there in a poundal?

    Every measurement system comes with bagfuls of obsolete and obscure units, even the (one of many) metric systems. How many people know what a sthene is?
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