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International System of Units overhauled in historic vote

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Re: International System of Units overhauled in historic vote

#101

Post by cesis »

ggcdn wrote: post #86
lb1lf wrote: post #24

Earlier quoted context omitted.

Fun (?) anecdote - metric apparently has been used in US engineering for quite a while; a petrolhead buddy of mine was puzzled as to all the fractions used on the drawings of his (I think) Chrysler Hemi V8 from the fifties - on a hunch, we converted a few to metric. Bingo. (Just making up a number here) 3.937" stroke? Why on Earth... Ah. 100.0mm. That's why.

Another anecdote - In structural engineering, US units are way easier to work with, and even in Canada, about 90% the buildings I work on use kips, ft, ksi, etc.

Also electronic device screen size is expressed in inches all over the world, also pipes are often inches, the same applies to nails.

Re: International System of Units overhauled in historic vote

#102

Post by zamadatix »

jbay808 wrote: post #87
microcolonel wrote: post #33

Earlier quoted context omitted.

I don't know about trade, but kilo standards were deviating by tens of micrograms from eachother, some things are sold at prices which warrant accounting for those micrograms, so a completely stable international definition seems helpful. Certain types of scientific instrument will need to be recalibrated to meet the new definitions.

Is there any scale in the world that can measure a kilogram to within the accuracy of a microgram? And if you buy a kilogram of something and they accidentally short you by a few micrograms, haven't you only overpaid by a few parts per billion? Even on a billion dollar order you've only overpaid by a few dollars...

For your first question some Kibble balances have accuracy parts per billion in measurement of the kilogram.

For your second question, agreed - no trade deals care about the accuracy of the new kilogram vs old.

Re: International System of Units overhauled in historic vote

#103

Post by khawkins »

redial wrote: post #76
reaperducer wrote: post #56

Earlier quoted context omitted.

I guess the next redefinition will happen if and when there's detectable drift in "fundamental" constants? And until then, all the metric fanbois will constantly tell you that metric is superior to imperial because its measurements are immutable. Until suddenly they are.

I've never heard anyone claim that as the reason for its superiority. Metric is superior because it makes sense as a system .

1/2 m = 50.00 cm, 1/2 ft = 6 in

1/3 m = 33.33 cm, 1/3 ft = 4 in

1/4 m = 25.00 cm, 1/4 ft = 3 in

1/6 m = 16.67 cm, 1/6 ft = 2 in

This is why imperial makes more sense to me than metric. If we had a base-12 number system, metric would be perfect, but base-10 is terrible under division. For practical divisors like these, imperial shines.

If you're doing science, metric makes more sense because units work out. But most all US science has already adopted metric.

Re: International System of Units overhauled in historic vote

#104

Post by pbhjpbhj »

Jedi72 wrote: post #45
3pt14159 wrote: post #12

This is probably the dumbest thing I'll type on HN. In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?

No I agree, it seems stupid. What we did is take a block of metal and call it a kilogram, figure out how many atoms are in 1/1000 of it (a gram) and call that a mole. What we should do is redefine the gram to be whatever 1e10 atoms of Hydrogen weighs, or something similar. When I read the headline I thought thats what they did, and I admit first reaction was "oh god I'm going to be dealing with conversions and associ…

1E10 atoms of hydrogen isn't a fixed mass.

Cf binding energy, electron excitation, E=mc^2 (the m there is m0, the rest mass; the full equation includes the momentum and "relativistic mass").

The situation is actually worse for hydrogen (cf hydrogen bonding).

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.htm... is a pretty coherent and readable approach to the subject.

Re: International System of Units overhauled in historic vote

#105

Post by jbay808 »

ggcdn wrote: post #86
lb1lf wrote: post #24

Earlier quoted context omitted.

Fun (?) anecdote - metric apparently has been used in US engineering for quite a while; a petrolhead buddy of mine was puzzled as to all the fractions used on the drawings of his (I think) Chrysler Hemi V8 from the fifties - on a hunch, we converted a few to metric. Bingo. (Just making up a number here) 3.937" stroke? Why on Earth... Ah. 100.0mm. That's why.

Another anecdote - In structural engineering, US units are way easier to work with, and even in Canada, about 90% the buildings I work on use kips, ft, ksi, etc.

They aren't easier to work with for any reason other than that sizes of standard components (pipes, beams, etc) are sized conveniently in US units and have US units printed on the spec sheets.

If you go overseas outside of North America, you find that the sizes of everyday objects are conveniently sized in metric, and building codes and standards and material strengths and densities are specified in SI units, and suddenly working with the metric system in those industries is easy and convenient.

Do you deal with building insulation? How would you interpret a material spec of "1 BTU ft/(in^2 hr °F)"? I had to work with these units in the US and it was not at all convenient.

Re: International System of Units overhauled in historic vote

#106

Post by School-Cotton »

Oletros wrote: post #94
School-Cotton wrote: post #66

Earlier quoted context omitted.

I already made it clear that I totally agree metric should be standard in engineering or scientific applications. I wasn’t aware that this isn’t the case in the US — thanks for the info. I believe it is at least 95% the case in the US and I think we should make every effort to get that to 100%. I still stand by my argument that it does not matter much for everyday life.

Why have two separate sets of unit systems?

Well, the point I was arguing was "why not" have two separate systems ?

As for "why" to have them, well there isn't a good reason intrinsically -- if there were a way to magically convert the US to metric overnight, it wouldn't bother me. It just seems very unlikely and difficult in a country as huge and culturally diverse in the US. Especially since, by the standards of the rich/developed world, the US is pretty poorly educated, and also very difficult to govern (Obamacare, a law that would have seemed like a moderate reform, relatively simple to pass in any parliamentary system, is the most radical change in any area of policy enacted by the US federal congress in the last decade).

The thing a lot of people miss about the ultra-gridlocked US system is that there's a huge gulf between it being obvious to most people that "we should enact some policy" and anything actually changing. The best answer to "why doesn't the US do this or that" is often just "its political institutions can't".

Since it's so unlikely to change, and given my argument that it isn't a big deal in practice, I guess my main point is that we rationally-minded people should stop worrying/complaining about it so much.

Re: International System of Units overhauled in historic vote

#107

Post by njarboe »

MichaelDickens wrote: post #73
kozak wrote: post #59

Earlier quoted context omitted.

24 and 60 do make sense because they are highly composite numbers: https://en.wikipedia.org/wiki/Highly_composite_number

You could say the same thing about most Imperial units, but most people still prefer the metric system.

I would say most people prefer the one they learned first. For doing science metric is usually better. Easier unit conversions. I think inches/feet are better for construction as you have more options at what level of accuracy you want to work with and splitting things up unless you need to have a fifth of something.

Re: International System of Units overhauled in historic vote

#108

Post by kps »

kozak wrote: post #59
ballenf wrote: post #35

Has a "metric" version of time ever been proposed? Seems odd to me that we're "ok" with divisions of 12 for time but not length. I guess for science seconds are basically the only measure of time that usually matters?

24 and 60 do make sense because they are highly composite numbers: https://en.wikipedia.org/wiki/Highly_composite_number

12 and 60 are superior highly composite numbers¹ — as is 360, the number of degrees in a circle and the number of days in a year (with a little engineering work TBD).

Speaking of circles, SI hasn't fixed Hz vs rad, have they?

¹ https://en.wikipedia.org/wiki/Superior_highly_composite_numb...

Re: International System of Units overhauled in historic vote

#109

Post by namirez »

3pt14159 wrote: post #12

This is probably the dumbest thing I'll type on HN. In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?

For the same reason that we use both temperature and energy and find them both useful. We can talk of the energy of an electron. On the other hand, temperature, is an statistical property defined for many particles.

Using mole (based on Avogadro constant) makes it easier to do statistical mechanics, but it's not a microscopic property like mass.

Re: International System of Units overhauled in historic vote

#110

Post by SamBam »

MichaelDickens wrote: post #73
kozak wrote: post #59

Earlier quoted context omitted.

24 and 60 do make sense because they are highly composite numbers: https://en.wikipedia.org/wiki/Highly_composite_number

You could say the same thing about most Imperial units, but most people still prefer the metric system.

That's actually exactly why I like working in Imperial when woodworking. You're composing and dividing things by 2 all the time, so a base-2 fractional system is great.
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