Unit conventions (SI versus others)

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The discussion centers on the United States' reluctance to fully adopt the International System of Units (SI), unlike most other countries. Participants express concern that the lack of SI adoption complicates education, particularly in physics, where unit conversions can hinder understanding of fundamental concepts. While some argue that SI is already used in scientific contexts within the U.S., others highlight the persistence of customary units in everyday life and industry, which can create confusion and inefficiencies. The conversation also touches on the historical context of the U.S. being metric since 1866 and the challenges of transitioning to SI, including economic implications for various sectors, such as sports and trade. Additionally, there are debates about the practicality of SI versus customary units, with some claiming that SI simplifies calculations while others assert that both systems can be effectively used depending on the context. Overall, the discussion reflects a deep-seated tension between tradition and modernization in measurement systems.
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Can anyone explain to me how it comes that US not have accepted the use of SI ?
Do you not understand the benefits ?

Would it not be more effective if the new generation of students could concentrate on understanding fundamental physics relations rather than struggle whith old-fashioned and confusing unit transformations ?

As far as I know it is only US beside Liberia and Burma who has not understod the importance of this.
Why ?
 
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JR Jonsson said:
Can anyone explain to me how it comes that US not have accepted the use of SI ?
Do you not understand the benefits ?

Would it not be more effective if the new generation of students could concentrate on understanding fundamental physics relations rather than struggle whith old-fashioned and confusing unit transformations ?

As far as I know it is only US beside Liberia and Burma who has not understod the importance of this.
Why ?

Struggle with confusing unit transformations? I don't think I ever had a physics class that didn't use SI, except the odd course that used Gaussian units. Certainty, no course ever asked me to convert foot pounds to Newton meters if that's what you mean.

So we do use SI primarily in science courses, and not Imperial units in the US.
 
But the US has been metric since 1866!
 
JR Jonsson said:
Do you not understand the benefits ?
I don't understand the benefits. Scientists and engineers are already free to use SI if they want, and so are manufacturers. So what are the benefits?
 
Choppy said:
This is best answered by The Frantics.
Thank you for that.
"YARDS! What happened to CUBITS!?"
:biggrin:
 
Dale said:
I don't understand the benefits. Scientists and engineers are already free to use SI if they want, and so are manufacturers. So what are the benefits?
It would be nice not to have fifty bajillion sizes of sockets in my set.
 
jbriggs444 said:
It would be nice not to have fifty bajillion sizes of sockets in my set.
So auto mechanics could reduce the cost of their tools. That would be a benefit to them, but tool manufacturers would lose sales so that would be a disadvantage to them.
 
  • #10
Dale said:
So auto mechanics could reduce the cost of their tools. That would be a benefit to them, but tool manufacturers would lose sales so that would be a disadvantage to them.
Although you can run an economy by paying one batch of people to make holes and another batch of people to fill them in and while both groups of people will consider this to be to their benefit, there are better options.
 
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  • #11
jbriggs444 said:
Although you can run an economy

Run? I thought you said "ruin". :woot:
 
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  • #13
JR Jonsson said:
Can anyone explain to me how it comes that US not have accepted the use of SI ?
Inertia.
 
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  • #14
256bits said:
Some non-SI units are still very much common ex calorie ( or does any country with SI as the legal system of measurement just outright ban and fine usage ??o0) )
https://www.nist.gov/pml/nist-guide-si-chapter-5-units-outside-si
Would be interesting to know, where Joule is actually used instead of calories. I mean, they don't get even this right, as usually all talk about cal and mean kcal. And I can't remember a correct weather report. I usually don't get understood very well, if I complain about temperatures above 300. But °C is SI you could argue. Well, that's right, although not logical, but e.g. °mC isn't allowed here. I vote for Delisle!

P.s.: I counted 89 (sic!) different miles on the Wiki page!
 
  • #15
JR Jonsson said:
Can anyone explain to me how it comes that US not have accepted the use of SI ?
Do you not understand the benefits ?
Maybe you would like to volunteer to come here (U.S.) and change all of the millions of property descriptions, all of which are relative to some township (36 square miles), and one or more sections (1 square mile = 640 acres) within the township.

Here is an example property description for a place in the state of Florida. Care to take a crack at this one?

metes-and-bounds[1].png
 
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  • #16
We have the benefit of hybrid units, e.g., kW/ft (linear power) and cal/g (specific enthalpy/energy), in one particular industry. Most of my reports have incorporated both units since they were used in the US, Europe and Asia. I much prefer SI/mks, or mixed units, e.g., W/cm.
 
  • #17
Mark44 said:
Here is an example property description for a place in the state of Florida.
Well, at least that description didn't use chains...

Although, mostly related to wildland fires, the LMAs still do, to a certain extent.... :oldeyes:

And then... there's also the good old DBH measurement... so if you want somebody to cruise your timber for a sale, try to find a real short person ... lol

I'm not even going to talk about log scaling, and the Scribner Decimal C rule....:oldgrumpy:
 
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  • #18
The drawback to the number 10, the basis of the metric system, is its lack of divisors. No one is complaining about a 24 hour day. One could invent a 10-part year, but then you'd lose the 4 seasons. Many things come in 12's. Some things come in 20's. When something is not metric, there's usually a very pragmatic reason to prefer that system of measure. I like inches and feet, also quarts and gallons. I hope they are not abolished.
 
  • #19
Helios said:
The drawback to the number 10, the basis of the metric system, is its lack of divisors.
Except most engineering applications, particularly in manufacturing, use decimals even when using inches.

Using divisions like 1/16 inch or 1/32 inch might work for construction, or something similar, but it doesn't work well in precision engineering and manufacturing. When it comes to small parts, we often use mils, or fractions of mils, and sometimes micro-inches.
 
  • #20
Tenths are convenient because we use base ten because we have ten fingers. I always said we ought to have evolved an extra finger.
 
  • #21
Ibix said:
Tenths are convenient because we use base ten because we have ten fingers. I always said we ought to have evolved an extra finger.
A penny for your thoughts! The Sumerians used the base 60 ...:biggrin:
 
  • #22
I know SI is in use in U.S as well as other units are common everywhere
As a step on the way you can use both old units and SI (as for "cal" and "J" on all food declarations in sweden)
My point is that physics is hard enough to understand without unit conversions.
I had a student some years back who went to U.S. For one year between the ordinary in Sweden (17-18 years old)
He was advised not to study physics because it was considered very difficult, but did so anyway because he liked it.
I asked how he had done when he was back.
"The physics was really easy", he said, "nothing new but all the conversions. But I just converted the given data to SI, solved the problem and gave the answer in the unit that was asked for. Nobody understod how I did, not even the teacher."

The benefits with SI is simply that physics (and offcourse all technical use of it) will be easier.
 
  • #23
JR Jonsson said:
I know SI is in use in U.S as well as other units are common everywhere
As a step on the way you can use both old units and SI (as for "cal" and "J" on all food declarations in sweden)
My point is that physics is hard enough to understand without unit conversions.
I had a student some years back who went to U.S. For one year between the ordinary in Sweden (17-18 years old)
He was advised not to study physics because it was considered very difficult, but did so anyway because he liked it.
I asked how he had done when he was back.
"The physics was really easy", he said, "nothing new but all the conversions. But I just converted the given data to SI, solved the problem and gave the answer in the unit that was asked for. Nobody understod how I did, not even the teacher."

The benefits with SI is simply that physics (and offcourse all technical use of it) will be easier.

Again, no proper physics course in the US is using anything but SI or other metric type units.

At most there may be problems given in one set of units and you're asked to convet to SI, but that's only normally in the very beginning when students are learning conversions of all sorts.

I don't know where your student went, but it isn't normal. Also any physics teacher should be able to convert any type of units and understand unit conversions.
 
  • #24
Vanadium 50 said:
But the US has been metric since 1866!

Yes, and the US Bureau of Standards redefined "customary" units in terms of metric standards. One inch is defined as exactly 2.54 cm. Congress allowed customary units to be used, probably thinking for the time being, but meaning metric units would never be used if it could possibly be avoided.
 
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  • #25
JR Jonsson said:
My point is that physics is hard enough to understand without unit conversions.
What's the big deal? Unit conversions aren't difficult. They're annoying and, at times, tedious, but they're hardly difficult. And as others have pointed out, physics courses typically use SI units.

"Nobody understood how I did, not even the teacher."
I don't believe this for a second.
 
  • #26
JR Jonsson said:
The benefits with SI is simply that physics (and offcourse all technical use of it) will be easier.
I disagree with this. SI is not particularly convenient for many physics disciplines. It is bad for both general and special relativity, it is bad for QM, it is not the best for electromagnetism, and it is not used without substantial modification for particle physics.

It works for medicine and biology. It works for engineering. It works for trade, but I think a blanket statement that it makes physics easier is excessive.
 
  • #27
OCR said:
Well, at least that description didn't use chains

As Mark44 pointed out in post 15, land measure in the US is based on the acre and changing it would be very difficult. Chain-link measure in land measure is compatable with the acre.

From google headline:

"A chain (ch) is a unit of length. It measures 66 feet, or 22 yards, or 100 links, or 4 rods (20.1168 m). There are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains (that is, an area of one chain by one furlong)."
 
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  • #28
I'm sorry if i expressed myself badly.
Offcourse you in this forum understand SI and it's benefits. That is why I am taking part in here.
What i meant was the uncovinience with the imperial units ( or what it's named) when dealing whith US technical matters, and US has some influence on the rest of world.

It is interessting that the question about units seems to be so emotional.

The history of SI started whith units for length, mass and time. When needed and an agrement was made, the units for other dimensions was introduced.
In the case of elektronics, chemistry and light I don't think there is so much to choose between, it is relative new fields so there is simply no old units to argue whith.

Regarding new disciplins in physics it's totaly meaningless to say that SI don't is good. There are totaly new dimensions so if needed the science comunity hopefully will agree on definitions for units if there are something to messure.

It's easy to convert units when you know how, that's wright, but it's so unconvinient and makes it harder to introduce understanding for the fundamental physics relations.

I am in the technical field as profession and countless examples of the problem whith different unit- systems.

Another aspect of this is the communikation between scientists and the craftsman. It's difficult to introduce new ideas when there is no common language.

I'm no liar, the story was true. It was some years ago but I'm afraid there still are some old units in school, in US as well as in the rest of this world.
And it will be some problems if technical students come's to the first employment with only SI in mind.

I started this thred in hope of ideas about how to overcome communikation problems and phasing out unnecessary old-fashioned systems where we can.
 
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  • #29
JR Jonsson said:
Offcourse you in this forum understand SI and it's benefits.
I am still not convinced that there are any particular benefits. So far all you came up with is that physics is easier, and I don't think that is particularly true.

SI is already used in the US where it is beneficial and not used where it is not beneficial.
 
  • #30
Dale said:
I am still not convinced that there are any particular benefits. So far all you came up with is that physics is easier, and I don't think that is particularly true.

SI is already used in the US where it is beneficial and not used where it is not beneficial.

You make me confused.
For me it is physics to calculate f.ex. the heat loss in a building, equippment as pipes, pump's, radiators and heatpump needed to keep the house warm.
Compare the calculations needed whith SI resp. Imperial units; is there no difference ?
 
  • #31
SW VandeCarr said:
As Mark44 pointed out in post 15, land measure in the US is based on the acre and changing it would be very difficult.
Well, yes, that was my point... I thought, anyway... ??
I did say... "well, at least that description didn't use chains"… right ?
SW VandeCarr said:
From google headline:
Oh!... maybe you didn't see my chain .link ... lol... :oldwink:

From Wikipedia:

"A chain (ch) is a unit of length. It measures 66 feet, or 22 yards, or 100 links, or 4 rods (20.1168 m). There are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains (that is, an area of one chain by one furlong)."BTW, another nybble of information:

A rectangle, 8 feet wide and 1 mile long also has an area of one of 1 acre.... :approve:
 
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  • #32
JR Jonsson said:
For me it is physics to calculate f.ex. the heat loss in a building, equippment as pipes, pump's, radiators and heatpump needed to keep the house warm.
Yes (I would lump that into engineering in my previous list). My point is that it is also physics to model collisions between galaxies and atomic spectra and orbits of comets and high energy particle collisions and electromagnetism. SI is not particularly beneficial for any of those.

In the USA, the SI system is already used where it is convenient and not used where it is not.
 
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  • #33
OCR said:
A rectangle, 8 feet wide and 1 mile long also has an area of one of 1 acre.... :approve:

8x5280=42240 sq ft, 1 acre=43560 sq ft (US)
 
  • #34
SW VandeCarr said:
8x5280=42240 sq ft, 1 acre=43560 sq ft (US)
OK, 8 feet wide in one mile is actually ‪0.969,697 acre... so it rounds to 1 acre.... :oldtongue:
You're right though....:thumbup:... :blushing:

I said:
A rectangle, 8 feet wide and 1 mile long also has an area of one of 1 acre...
That's an old rule of thumb in farming... used to estimate how many acres per hour you can do...
An example... our grain drills are each 8 feet wide, and we pull 5, hitched side to side, so that makes a 40 foot wide swath, or, about 5 acres in a mile.
If we go about 6 MPH, we can do about 30 acres per hour.... :oldsmile:

Lol, it does take some pretty big thumbs for that to happen though, considering overlap and the directional changes...
 
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  • #35
The difficulties faced by the US in converting completely to metric units, let alone SI, go beyond land measure. Consider the economic impact of professional sports. It's a big deal for major US cities who compete for franchises. Football would be played on a 91.44 meter long field. A first down requires a gain of 9.144 meters after 4 downs. You could rescale the game to 100 meters, but that changes the game. In baseball, the impact of rescaling is even greater. Alternatively we could just use percents: the 50 % line for the coin toss and spotting the ball on the 20% line after the kickoff. It might take some getting used to distance gained or lost in percents rather than yards. In baseball, we could just mostly ignore the numbers and get used to 100 meter home runs.

Or we could just ignore the whole issue and use whatever units we want. That seems to have been the real intention of Congress way back in 1866 when the US became officially metric.

EDIT: For units used in commercial transactions, I believe these units are required to be those that are precisely defined in terms of metric units by the US National Institute of Standards and Technology (NIST).

https://en.wikipedia.org/wiki/United_States_customary_units
 
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  • #36
OCR said:
If we go about 6 MPH, we can do about 30 acres per hour.... :oldsmile:
Yeah, but what would that be in square furlongs per fortnight? (I.e. in ##\frac{\text{furlong}^2}{\text{fortnight}}##)
 
  • #37
  • #38
I did not see this image in the thread, so I'll go right ahead and post it... (even though "The rest of the World" is not entirely accurate)
imperial-vs-si.png


Bonus joke:
degrees.png
 
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  • #39
DennisN said:
I did not see this image in the thread, so I'll go right ahead and post it... (even though "The rest of the World" is not entirely accurate)
imperial-vs-si.png

Yes, but none of this is worth damaging the great institution of AMERICAN FOOTBALL. As I said in post 35, we cannot have 9.144 meter intervals nor can we have a 100 meter long fields. The game is sacrosanct. Nor is it acceptable to make an exception for football by allowing the game to keep its beloved "yard" That will cause gas stations, supermarkets, horse traders and who knows who else to demand exceptions. Our Congress cannot resist making exeptions to the point where it might even abolish the metric labels that already exist on canned soup.
 
  • #40
SW VandeCarr said:
Yes, but none of this is worth damaging the great institution of AMERICAN FOOTBALL. As I said in post 35, we cannot have 9.144 meter intervals nor can we have a 100 meter long fields. The game is sacrosanct. Nor is it acceptable to make an exception for football by allowing the game to keep its beloved "yard" That will cause gas stations, supermarkets, horse traders and who knows who else to demand exceptions. Our Congress cannot resist making exeptions to the point where it might even abolish the metric labels that already exist on canned soup.
Hmm, maybe the president could ask Congress to redefine the conversion to 1 yard = 1 meter. Just an idea. (sorry, I could not resist :smile:)
 
  • #41
DennisN said:
I did not see this image in the thread, so I'll go right ahead and post it... (even though "The rest of the World" is not entirely accurate)
imperial-vs-si.png
It's ironic that the graphic on the right is subtitled 'Logical Smooth Sailing,' since SI units are actually not very convenient for that! (Try looking at navigational charts and you'll know what I mean.)
Bonus joke:

:smile:
 
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  • #42
fresh_42 said:
Would be interesting to know, where Joule is actually used instead of calories. I mean, they don't get even this right, as usually all talk about cal and mean kcal. And I can't remember a correct weather report. I usually don't get understood very well, if I complain about temperatures above 300. But °C is SI you could argue. Well, that's right, although not logical, but e.g. °mC isn't allowed here. I vote for Delisle!

P.s.: I counted 89 (sic!) different miles on the Wiki page!
This miles : https://en.wikipedia.org/wiki/Myles_Standish is called "Kilometre Deboutish" In France *

* Not my original.
 
  • #43
Dale said:
I don't understand the benefits. Scientists and engineers are already free to use SI if they want, and so are manufacturers. So what are the benefits?
A very minor one: in supermarkets, in order to compare products you must compare gallons with pounds, ounces, etc. Some products include measures of both volume and weight, maybe others. So , unless you know the density and can do things in your head, or you carry a calculator, it becomes a mess.
 
  • #44
f95toli said:
People forget that the SI is mainly a practical system for use in our everyday lives (which is why the Candela is a base unit) ; meaning practical considerations are more important that what is most satisfying from a philosophical point of view.
0000

That's really funny, LOL! The unit sizes, in many cases, are completely absurd. Measure a small distance in meters (say the diameter of a pencil); much easier in inches. Measure your weight in Newton? Its already too much in pounds. Measure your tire pressure in Pascals? It takes 100000 of them to get up to atmospheric pressure.

Sure, I know about prefixes. Handy stuff like, for example, a (kilo-)^2 in the numerator will cancel a mega- iin the denominator.

Please don't try to sell SI based on practicality; it does not work.
 
  • #45
Dr.D said:
Please don't try to sell SI based on practicality; it does not work.
I prefer a metric system over any of such absurdities like inches and miles. Do you know how many versions a mile has? Dozens! The centimeter and the kilometer do far better jobs than inches and miles. It is practical. The reason that some refuse to use it cannot be accounted as an argument against practicability. And if you don't like Pascal, then use bar, it's that easy. MKSA is a reasonable system and it is proven practical for the large majority of countries.
 
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  • #46
Dr.D said:
Please don't try to sell SI based on practicality; it does not work.

it does work and very well

fresh_42 said:
I prefer a metric system over any of such absurdities like inches and miles. Do you know how many versions a mile has? Dozens! The centimeter and the kilometer do far better jobs than inches and miles. It is practical. The reason that some refuse to use it cannot be accounted as an argument against practicability. And if you don't like Pascal, then use bar, it's that easy. MKSA is a reasonable system and it is proven practical for the large majority of countries.

Hear Hear ! totally agree
 
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  • #47
f95toli said:
People forget that the SI is mainly a practical system for use in our everyday lives (which is why the Candela is a base unit) ; meaning practical considerations are more important that what is most satisfying from a philosophical point of view.
Dr.D said:
That's really funny, LOL! The unit sizes, in many cases, are completely absurd.
I think "practical" is better understood here as "practical to accomplish precisely and repeatably in the laboratory." It would be appealing from a philosophical or aesthetic point of view to define the unit of charge in terms of the charge on some number of protons or electrons, but that requires some way to count the number of protons or electrons in a sample.

Those who want elegance can use Gaussian units instead, as theorists in fact generally do, in which the unit of charge (the statcoulomb) is defined using Coulomb's law, by setting the proportionality constant to 1 instead of the "wierd" 1/4πε0.

Any size unit is going to be "practical" in terms of its numeric values only in some contexts.
 
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  • #48
jtbell said:
Any size unit is going to be "practical" in terms of its numeric values only in some contexts
That's very obvious but it clearly needed saying. Not many people have problems with c,M,k,m and μ etc..
Something that does make me smile is how the odd intermediate multipliers like d and D are used in some businesses - just because they were established a while ago. And then there's Angstroms. How can that possibly be a serious unit these days?
 
  • #49
sophiecentaur said:
Angstroms. How can that possibly be a serious unit these days?

indeed, but astronomers and a few other still seem to have a fond attachment to it
All these optical filters, like my solar filter" are all rated with an Angstrom bandwidth rather than using nanometres
 
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  • #50
davenn said:
indeed, but astronomers and a few other still seem to have a fond attachment to it
All these optical filters, like my solar filter" are all rated with an Angstrom bandwidth rather than using nanometres
It is still a meter, so the confusions are limited. AU, ly and kpc are not, but also in use and nobody complains. Maybe it's a bit of a silent revenge, because Americans can't write Ångström. :biggrin:
 
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