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Big Test Coming Up For Kilogram Redefinition (ieee.org)
szotz writes: Electromechanical balances have got to be better than an aged lump of platinum and iridium right? Teams are working to get kilograms measured and shipped to Paris in time for a test to see whether the technology (along with another that uses ultrapure silicon spheres) is now ready to redefine the kilogram. Why is this redefinition interesting? Because it's about using physics to overcome one problem with weight standards based on tightly held exemplars in standards bodies' inner sanctums: the mass of those exemplars can change, however subtly, introducing uncertainty and confusion. From the article: The world's metrologists aim to change this state of affairs in 2018 by fixing the kilogram to the Planck constant, a fundamental physical constant. That shift would, at least in principle, allow any laboratory to "realize" the kilogram from scratch with a series of experiments and specialized equipment. But for that scheme to work, the kilogram derived by one laboratory must be the same as those derived by others.
So really it is just a global scientific test of who's is bigger.
Sounds like they won't be needing that kilo of platnium anymore... Send it to me please.
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Why the planck constant then? Why not e, or (pi), or any other constant, for that matter? If you're going to change the definition, isn't it just a matter of choosing the close enough factor?
By the way, I'm asking. I am ignorant about this.
The fundamental distinction between math and physics is measurement. We need to base the physical constants on something measured from the universe we're interested in.
As a simple example, mathematics defines and explores 3 basic forms of geometry: Euclidean, hyperbolic, and elliptic.
The distinction between these is based on the curvature of space as defined by the behaviour of parallel lines: if parallel lines eventually meet, then space has positive curvature like the surface of a sphere. If parallel lines diverge, then space has a negative curvature like the surface of a saddle. And if parallel lines stay parallel, then space has zero curvature and is Euclidean.
Three equally valid forms of geometry, but which one does the universe have? To choose the correct model, we have to measure the actual universe.
The same is true with the fundamental physical constants. There's any number of ways to base our measurements on pure math, but these don't necessarily reflect the reality we live in.
To do that, we need to take a measurement.
e and pi are numbers. You need actual physical constants like the mass of a proton or Planck's cpnstant.
It is indeed just a matter of choosing "close enough factor", but close enough (to avoiding needing to redo or change any measurements that anyone uses) is pretty close, about one part in 100 billion. Being sure that we have done that is the hard part.
This is a massive development.
Don't waste your vote! Vote for whoever you want, unless you live in a swing state it won't matter anyways
Weight Watchers International weighted in on the discussion requesting the new kg to be defined at twice the weight of the current kg ("Yes Sandy, I lost half of my weight in the blink of an eye!"), while grocers all over the planet petitioned to divide the current value by four.
All kilograms are equal
but some are more equal than others.
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Shouldn't it be the "general" definition? Fuck the metal weight - 1 kg is 1 liter of (distilled/pure) water (at 1 atmosphere pressure)? The amount of heavy hydrogen messes it up? 1 atmosphere of pressure isn't the same at all places on the earth due to varying gravity?
Perhaps; but it'll always be true that a pint's a pound the world 'round.
#DeleteChrome
I bet they're going to change the definition from 1 kg = 1024 grams to 1 kg = 1000 grams. And we'll probably have to write "kig" too to make sure we don't get confused about the old definition.
And have Bill Gates switch off the internet to save your children.
Yes. How many atoms are there in 1 liter? I guess you could go more 'general' and say how many drops of water? But then, how big are the drops of water? What about the absorbtion rate of the material, can it only be measured in glass? is this deformed at 1 atmosphere pressure? evaporation rates?
Then you get to mineral/chemical impurities, atmospheric disturbances, etc.
Maybe 1 kg vs 0.999997 kg doesn't mater to you but there are many cases where it will. And calibrating our scales to allow that fine-grained approach is nothing but a Good Thing.
The unit formerly known as the "pound" shall now be called the "kilogram". The prices will be adjusted accordingly.
The Pound is defined as a fraction of a kilogram...
Whatever standard you adopt needs to be reproducable within the limits of the best current measurements by any other technique. Otherwise when people want a stable reproducible result they will use the other technique and the standard won't have worked. Measuring volume of water, purity, temperature and pressure is just not precisely reproducible enough
First we define what Avogadro's number is. Based on a measurement of the number of atoms in a silicon sphere of known mass. The ratio between the weight of a single silicon atom and plancks constant is already known, so this would give us a way to convert from plancks constant to a new definition of a kilogram.
Of course, measuring the number of atoms in a silicon sphere is hard to reproduce. Enter the other competing method, the watt balance.
Place an object on a speaker cone, then measure the current required to hold it aloft. Move the speaker cone, measure both the created voltage and the velocity. We can use these measurements of current, voltage, velocity and a measurement of the local acceleration of gravity, to calculate the mass of the object. This is equivalent to measuring the value of an electrical watt in SI units, which allows us to also compare the measured mass to plancks constant.
09F91102 no, 455FE104 nope, F190A1E8 uh-uh, 7A5F8A09 that's not it, C87294CE no. Ah! 452F6E403CDF10714E41DFAA257D313F.
So it'll be 999.000000001 grams or something?
Maybe they'll redefine gram one of these days
Isn't a litre 1kg of pure water at normal room temperature and normal atmospheric pressure, so presumably that will change if the definition of 1kg changes?
I don't know why they don't switch a litre to being 1000cc.
By definition, 1 litre is 1 dm^3, which is exactly 1000 cc (1 cc = 1 cm^3), units of volume are derived from length, not mass.
And about 1 litre of pure water having a mass of 1kg at 1 atm, yes, but not at room temperature, at 4C instead, and it was the initial definition of a kg.
I have discovered a truly marvelous proof of killer sig, which this margin is too narrow to contain.
By definition, 1 litre is 1 dm^3, which is exactly 1000 cc (1 cc = 1 cm^3)
That's actually incorrect and in reality 1cc = 0.99997ml. You can see this in various text books, for example the "Handbook of Chemistry and Physics" or "A Laboratory Textbook of Anatomy and Physiology":
https://books.google.co.uk/books?id=Av-xb_AEHmIC&pg=PA529&lpg=PA529&dq=1+cc+%3D+0.99997+ml&source=bl&ots=rv-eGLZ9xW&sig=s9Y3m8NRmuEWF-H1me-ON49avIk&hl=en&sa=X&ved=0ahUKEwiSxcmur5DLAhWIVxoKHQmRCtYQ6AEIKDAC#v=onepage&q=1%20cc%20%3D%200.99997%20ml&f=false
I believe the discrepancy is caused by the weight of the kilogram being poorly defined. That's why I wonder if the litre will have to be redefined if the kilogram is redefined and why I said I think it would be better to use 1000cc for the definition of a litre.
Not in the UK, where a pint of water weighs a pound and a quarter.
That seems rather daft.
Surely an ounce should be defined in terms of grams.
Initially, 1kg was defined as the weight of 1 litre of water but it changed because it isn't something that is easy to measure accurately. Currently, there is no link between mass and volume.
The litre is just an alias for the cubic decimeter, the same way that the (metric) ton is just an alias for the megagram. Just different names for the same thing. So 1 litre is and has always been 1000cc or 0.001m3.
...the Imperial system of weights and measures is bad because it's "arbitrary".
-Styopa
I thought it was a stupid conversion mistake, but investigating on the topic :
One litre of liquid water has a mass of almost exactly one kilogram, due to the gram being defined in 1795 as one cubic centimetre of water at the temperature of melting ice.
So, originally as I wrote.
From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at maximum density and standard pressure. The kilogram was in turn specified as the mass of a platinum/iridium cylinder held at Sèvres in France and was intended to be of the same mass as the 1 litre of water referred to above. It was subsequently discovered that the cylinder was around 28 parts per million too large and thus, during this time, a litre was about 1.000028 dm3.
Oops. Not too bad, given that at that time the metre was wrong too:
it was later determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre.
And all is fine again:
In 1964, the definition relating the litre to mass was abandoned in favour of the current one.
The litre [...] is an SI accepted metric system unit of volume equal to 1 cubic decimetre (dm3), 1,000 cubic centimetres (cm3) or 1/1,000 cubic metre.
Sources:
Litre
Metre
I have discovered a truly marvelous proof of killer sig, which this margin is too narrow to contain.
Because if Planck's constant changes - every law of physics is diffferent and we can't make any predictions about how. Seriously, a universe where Planck's constant is different could be 3x3m square vaccuum containing a single deck chair. There is nothing in modern physics that preclude the big bang forming into this tiny pet universe with it's comfortable single amalgamation of matter that is NOT dependent on Planck's constant being the one we know.
Unicode killed the ASCII-art *
Actually - it would make more sense to define that one the other way around. If you have an atomic-accuracy measurement for mass, then it's much more sensible to define volume from mass than the other way around: so you would instead define liter as "the volume of a kilogram of water when these conditions are all at these specific values".
Unicode killed the ASCII-art *
The US approach is silly. The apparatus must be isolated from the environment to such a degree that it is impractical. Oner must monitor and dissuade wildlife a quarter mile away from the apparatus to get useful measurements. In essence the US approach is not to make a standard but a very impractical scale. The German approach is not so touchy. There is nonsense about only one Australian guy being able to form the spherical reference but that is ridiculous cult of personality. The German approach is both defined by a physical description and produces an actual physical kilogram reference. The US approach has the wow factor of a physical constant used to define the kilo but who cares? The US approach would result in inconsistent kilos if adopted. Anything that touchy is not suitable as a definitive reference.
It should be defined by Pope Francis
He used to be a chemist, and is infallible.
There is great deal of variation throughout the world, to the extent that the saying I was taught was "A pint's a pound the world 'round...within 5%" [more]
I come here for the love
except your 1 atmosphere is 101325 Pa, a Pa being 1 newton per square meter, a newton being defined as force needed to accelerate *1 kilgram* at 1 meter per second squared
do you see any problem?
This was the definition for a few years in the eighteenth century, before it was quickly changed.
It's such a bad definition, it was not worthy using even back then.
That was the definition of a kilogram for a few years, several centuries ago. You're a little bit out of date.
That's right, I take every an AC says with a grain of salt and a fifth of tequila.
After all my standard is that 1 us dollar equals 1 million US dollars and that is true because my own world view says so
[/sarcasm may be present in the above. Read at your own risk. Not liable for any stupidity you get on you]
i thought once I was found, but it was only a dream.
the SI unit is the kilogram, not the gram. The gram is defined as 1/1000 of a kilogram.
> Why the planck constant then? Why not e, or (pi), or any other constant, for that matter?
Because:
a) the universe is quantized / discrete / digital,
b) Plank Length and Planck Time are thought to be the smallest possible divisions of space and time respectively, (if there are any smaller divisions we're unable to measure them)
c)
Planck units also has this interesting tidbit:
Cleaning up the "sloppy" definition of kg for something extremely precise is LONG overdue.
However, the bigger problem with the SI system is that the 7 fundamental (sic.) units are NOT independent from one another; that is, the definitions for Candela, Mole, Amp and Kelvin, are *dependent* upon the definition of the kg !? Worse, the mole and candela are completely _redundant_. So much for being "fundamental units."
See this pic:
http://www.blazelabs.com/pics/...
--
When are Scientists going to discover the 6 fundamental forces?
Use the D1 discussion system. It still works just fine, and it has both a dropdown and a "confirm" button. Find it in your account options under 'Discussion'.
Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
It's more than 2.2 times better..
Which itself is daft, considering the morpheme kilo-
But we already have one for the liter?
"1 liter = 1.18101066 Ã-- 10^(-51) cubic light years"
(that one likely rounded off but you get the idea.)
"Add one 6 Ã-- 10^(-54) cubic light years of tea-leaves per cup."
The idea was that 1 atmosphere would be the the pressure of 10 meters of water (where?! :D) and it would all be solved out by having the same water and the same light-speed.
Bwah, imperial is better: ;D
One liter = "The volume of the brain-substance you easily can scrape out with some residues left in the skull."
That wouldn't be a problem, because the universe would change accordingly, and the kilogram in relation to the rest of the universe would remain unchanged.
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In fact, the litre *could* be redefined to be exactly 1kg of water and simultaneously exactly 1dm^3 of water. The definition just needs to adjust the atmospheric pressure and temperature of water at the moment of measurement - while thermal and pressure expansion/compression of water is minuscule, a change by 0.003% is well within reasonable limits of what occurs on Earth.
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> Why exactly is this a problem?
"Proposed_redefinition_of_SI_base_units#Impact_on_base_unit_definitions"
https://en.wikipedia.org/wiki/...
> You don't have to advertise that
I don't get it why you always keep confusing those two. The one for implants is called silicone.
Capito?
But my balls are sandy.
(people, my point was that if the universe is contracting or expanding, something as co-involved as Planck's constant could easily change and we wouldn't be able to measure it as all of our measuring devices and things they're measuring would be contracting or expanding simultaneously. sheesh. how i got downvoted to 0 on a subject that sprang so much discussion is typical slashdot and yet completely beyond me.)
"Stratigraphically the origin of agriculture and thermonuclear destruction will appear essentially simultaneous" -- Lee