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For decades, metrologists have strived to retire ‘Le Grand K’ — the platinum and iridium cylinder that for 126 years has defined the kilogram from a high-security vault outside Paris. Now it looks as if they at last have the data needed to replace the cylinder with a definition based on mathematical constants.
The breakthrough comes in time for the kilogram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures (CIPM) will meet in Paris to thrash out the next steps.
“It is an exciting time,” says David Newell, a physicist at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. “It is the culmination of intense, prolonged efforts worldwide.”
[...] In 2011, the CIPM formally agreed to express the kilogram in terms of Planck’s constant, which relates a particle’s energy to its frequency, and, through E = mc2, to its mass. This means first setting the Planck value using experiments based on the current reference kilogram, and then using that value to define the kilogram. The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.
(Score: 2) by schad on Friday October 16 2015, @01:30AM
Eh. I'm American, and honestly, it entirely depends on what you grew up with. I'm utterly hopeless with US units of volume, for instance, because I learned science before I learned to cook. My wife gives me shit every time I try to cook something because I have to look up conversion tables on my phone every 30 seconds.
It's really kind of strange how it works. 62mph seems very ordinary to me, but 100kph is hard to grasp. Tell me 91 ft/sec and I'm lost, but 28 m/s makes total sense. Tell me your car has a 349 cu-in engine and I'll give you a blank stare. But tell me that it's 5.7 L and I'll be duly impressed. At the small end, I have no problem visualizing 10mm (it's a common bolt head size) but 3/8" is weird. And forget about shit like 15/32" -- I have to think just to understand which side of 1/2" that's on (I wish I were kidding). Even after realizing that those "odd" sizes are almost always just 1/n to either side of 1/2 (15/32 = 1/2 - 1/32) I still struggle with it.
The most annoying thing about the US system is definitely that every type of unit has probably 5 or 10 different names. Teaspoon, tablespoon, cup, quart, gallon -- all units of volume. Is it really so hard to say "4 cups" instead of "quart?" (It's 4 cups to a quart, right?)
(Score: 1) by Francis on Friday October 16 2015, @01:54AM
This kind of reinforces my belief that people that don't know the imperial system shouldn't be knocking it.
1 cup is 8 ounces. 1 pint is 16 ounces, 1 quart is 32 ounces, 1 gallon is 128 ounces. The only bit that gets a tad confusing is that a tablespoon is 1/16 of cup. But in general, you don't normally go between cups and tablespoons or teaspoons very often. The only time that happens is if a recipe calls for 1/4 cup of something and you need to go smaller. If you find that annoying, you can mostly dispense with those and use fluid ounces. It's not really that hard to go with .5 fluid ounces in a table spoon and so forth.
Yes, that sounds confusing, but really, you spend 10 minutes learning it and then you get to benefit from the utility of the system. You can start using all sorts of cups that aren't technically measuring cups for measuring. A 16 ounce cup that you use for drinking is all of a sudden double the size of a measuring cup. Which is a real convenience if you don't have an extra measuring cup on you.
As far as visualizing, why on earth would you be visualizing that sort of crap? 15/32" is just slightly smaller than half an inch. 349cu-in isn't really any harder or easier to visualize than 5.7L is. In both cases it's a relatively small engine.
(Score: 2) by tangomargarine on Friday October 16 2015, @02:45AM
Dividing something in half is rather easier to eyeball than into 10 as well.
Imagine trying to cut a yardstick/meterstick into 10 equal pieces without using the markings. First you cut it in half...then...hmm...you have to figure out a good way to eyeball cutting it into equal fifths.
(but of course a yardstick is a multiple of 3 so that doesn't work either...except foot is 12 which is divisible by 2, 3, 4, and 6 so you can do some juggling)
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"