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International System of Units overhauled in historic vote

npl.co.uk

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Re: International System of Units overhauled in historic vote

#151

Post by gattr »

eutropia wrote: post #61
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?

Heinlein's "Starship Troopers" has the space marines using "kiloseconds" and "megaseconds" conversationally, and it was always tricky for me to convert those to hours and minutes in my head accurately.

And in Dukaj's "Perfect Imperfection" [1] occasionally multiples of Planck time are used (with metric prefixes), as the post-humans and "out-of-space computers" can operate on very small time scales.

[1] https://en.wikipedia.org/wiki/Perfect_Imperfection

Re: International System of Units overhauled in historic vote

#152

Post by ChuckMcM »

pfbtgom wrote: post #83

How would you use the new definition to calibrate instruments? My current understanding is that there is a lineage of artifacts calibrated against another artifact until one of those was calibrated against the one true artifact. So how would NIST or another certifying source say that my 1kg standard is 1kg +/- tolerance? Is it anyone with a kibble balance can now certify calibrations? How do you know your kibble bala…

The pictures in that article about NIST reminds me of the adage, "The smaller the measurement, the bigger the lab."

I like to use metrology labs as an example of something people often take for granted (measuring things) and showing how deep that invisible rabbit hole goes.

Re: International System of Units overhauled in historic vote

#153

Post by jackpirate »

jcranmer wrote: post #114
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?

Understanding mass in molar terms is necessary to do a lot of chemistry correctly. The mole is effectively a count of the number of molecules kicking about, although the count is large enough that terms like "quadrillion" don't cut it. (One mole is about 600 sextillion molecules). Knowing how many molecules are around lets you actually compute how much stuff can react in a given chemical environment, and other aspect…

I think the GP is making the claim that Avogadro's constant should be 1 (effectively eliminating it), not that there's no need to count molecules.

Re: International System of Units overhauled in historic vote

#154

Post by jimktrains2 »

piano wrote: post #21
throwaway2048 wrote: post #10

Earlier quoted context omitted.

It does actually, US measurements are legally defined in terms of metric units. https://en.wikipedia.org/wiki/United_States_customary_units

They really should cut the middle man. What surprised me reading that wiki page is that apparently the metric system was opposed in the US based on religious reasons . That is mind-boggling.

I've actually become quite fond of liquids being powers of 2 and lengths being broken fractionally. The base unit doesn't really matter (and you can always use decimal length, as is often done when building precision items).

So, for liquids,

2 tablespoon = 1 ounce 2 ounce = 1 jack 2 jack = 1 gill 2 gills = 1 cup 2 cup = 1 pint 2 pint = 1 quart 2 quart = 1 pottle ( ½ gallon) 2 pottle = 1 gallon

I find it much easier to switch units and do conversions in my head, especially when scaling recipes.

With respect to base-2 fractional length measurements, I just find it much easier to work with fractions than than with decimals. Half of ⅛ is ¹/₁₆ with next to no thought. I don't need to do division of 25 to get 12.5. It's a personal thing, but I find it nice.

Re: International System of Units overhauled in historic vote

#156

Post by tzs »

artimaeis wrote: post #123
Digit-Al wrote: post #119

Can anyone tell this poor ignoramus whether the kg is getting heavier or lighter - and how much by (approximately, I know it's not going to be an exact figure given the reason they are changing it)?

The mass of the kilogram is remaining the same. These changes don't affect the "size" of any of the units. > "[...] the size of these units will not change (a kilogram will still be a kilogram) [...]"

> These changes don't affect the "size" of any of the units.

The size of electrical units is changing slightly. According to this BIPM document [1]: "The transition from the 1990 convention to the revised SI will result in small changes to all disseminated electrical units. For the vast majority of measurement users, no action need be taken as the volt will change by about 0.1 parts per million and the ohm will change by even less. Practitioners working at the highest level of accuracy may need to adjust the values of their standards and review their measurement uncertainty budgets".

[1] https://www.bipm.org/utils/common/pdf/SI-statement.pdf

Re: International System of Units overhauled in historic vote

#158

Post by whoopdedo »

eutropia wrote: post #61
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?

Heinlein's "Starship Troopers" has the space marines using "kiloseconds" and "megaseconds" conversationally, and it was always tricky for me to convert those to hours and minutes in my head accurately.

I'm sure measuring "days" becomes silly when you're not spending a significant amount of time on a rotating spheroid orbiting a single star.

Rounding up to 4Ks is a reasonable substitute for an hour. Also gives you the convenient 15min ~ 1Ks or "a quarter of a metric hour."

Re: International System of Units overhauled in historic vote

#159

Post by ggcdn »

jbay808 wrote: post #105
ggcdn wrote: post #86

Earlier quoted context omitted.

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 sud…

I don't deal with building envelope. Its not surprising or unexpected that there are differing opinions among various professions on which set of units are more convenient.

In Canada, all our building code, material design codes, etc are in metric, and yet we are still using US units for day to day design.

Re: International System of Units overhauled in historic vote

#160

Post by tbirrell »

bryondowd wrote: post #133
eutropia wrote: post #79

Earlier quoted context omitted.

(10/24) (100/60) (100/60)=1.1574 Our biggest revolution yet: extending the length of the day by 16%!

Presumably, the second was shorter, rather than the day was longer. EDIT: More specifically, if you take an average rotation of the Earth as 86164.1 seconds, and divide by 10, then 100, then 100, you get 0.861641, which would be the conversion from our seconds to the metric second in that scenario. Likewise, the metric minute would be 86.1641 of our seconds or about 1.43607 of our minutes, the metric hour would be 86…

You could just define the second to be a 1/100,000 of a day and go from there. Aside from screwing with literally everyones perception of time, it could work.
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