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supercollider
superconducting



Registered: 10/13/00
Posts: 1,234
Loc: Waxahachie
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The Kilogram is Shrinking!
#7423575 - 09/18/07 12:42 PM (16 years, 4 months ago) |
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http://www.physorg.com/news108836759.html
Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.
"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," he said. "We don't really have a good hypothesis for it."
The kilogram's uncertainty could affect even countries that don't use the metric system - it is the ultimate weight standard for the U.S. customary system, where it equals 2.2 pounds. For scientists, the inconstant metric constant is a nuisance, threatening calculation of things like electricity generation.
"They depend on a mass measurement and it's inconvenient for them to have a definition of the kilogram which is based on some artifact," said Davis, who is American.
But don't expect the slimmed-down kilo to have any effect, other than possibly envy, on wary waistline-watchers: 50 micrograms is roughly equivalent to the weight of a fingerprint.
"For the lay person, it won't mean anything," said Davis. "The kilogram will stay the kilogram, and the weights you have in a weight set will all still be correct."
Of all the world's kilograms, only the one in Sevres really counts. It is kept in a triple-locked safe at a chateau and rarely sees the light of day - mostly for comparison with other cylinders shipped in periodically from around the world.
"It's not clear whether the original has become lighter, or the national prototypes have become heavier," said Michael Borys, a senior researcher with Germany's national measures institute in Braunschweig. "But by definition, only the original represents exactly a kilogram."
The kilogram's fluctuation shows how technological progress is leaving science's most basic measurements in its dust. The cylinder was high-tech for its day in 1889 when cast from a platinum and iridium alloy, measuring 1.54 inches in diameter and height.
At a November meeting of scientists in Paris, an advisory panel on measurements will present possible steps toward basing the kilogram and other measures - like Kelvin for temperature, and the mole for amount - on more precise calculations. Ultimately, policy makers from around the world would have to agree to any change.
Many measurements have undergone makeovers over the years. The meter was once defined as roughly the distance between scratches on a bar, a far cry from today's high-tech standard involving the distance that light travels in a vacuum.
One of the leading alternatives for a 21st-century kilogram is a sphere made out of a Silicon-28 isotope crystal, which would involve a single type of atom and have a fixed mass.
"We could obviously use a better definition," Davis said.
-------------------- Supercollider? I just met her!
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Madtowntripper
Sun-Beams out of Cucumbers



Registered: 03/06/03
Posts: 21,287
Loc: The Ocean of Notions
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I thought that silicon crystal was under production?
-------------------- After one comes, through contact with it's administrators, no longer to cherish greatly the law as a remedy in abuses, then the bottle becomes a sovereign means of direct action. If you cannot throw it at least you can always drink out of it. - Ernest Hemingway If it is life that you feel you are missing I can tell you where to find it. In the law courts, in business, in government. There is nothing occurring in the streets. Nothing but a dumbshow composed of the helpless and the impotent. -Cormac MacCarthy He who learns must suffer. And even in our sleep pain that cannot forget falls drop by drop upon the heart, and in our own despair, against our will, comes wisdom to us by the awful grace of God. - Aeschylus
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maggotz


Registered: 06/24/06
Posts: 7,539
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i had read about the avogadro project and the watt balance a while back. i think they're trying a bunch of other methods to redefine the kilogram also.
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Diploid
Cuban



Registered: 01/09/03
Posts: 19,274
Loc: Rabbit Hole
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The Kilogram is Shrinking
Aha! Now I know why my weed disappears so fast!
-------------------- Republican Values: 1) You can't get married to your spouse who is the same sex as you. 2) You can't have an abortion no matter how much you don't want a child. 3) You can't have a certain plant in your possession or you'll get locked up with a rapist and a murderer. 4) We need a smaller, less-intrusive government.
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demiu5
humans, lol


Registered: 08/18/05
Posts: 43,948
Loc: the popcorn stadium
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how does a fictitious unit of measure shrink?
-------------------- channel your inner Larry David
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Rustifer
prestige worldwide



Registered: 04/10/05
Posts: 7,071
Loc: Central Texas
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Re: The Kilogram is Shrinking! [Re: Diploid]
#7424279 - 09/18/07 03:31 PM (16 years, 4 months ago) |
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Quote:
Diploid said: The Kilogram is Shrinking
Aha! Now I know why my weed disappears so fast!
hahahaha.
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Seuss
Error: divide byzero


Registered: 04/27/01
Posts: 23,480
Loc: Caribbean
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Re: The Kilogram is Shrinking! [Re: Rustifer]
#7424503 - 09/18/07 04:39 PM (16 years, 4 months ago) |
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I'm curious why the one is shrinking rather than the others growing?
-------------------- Just another spore in the wind.
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skydog
Coffee & Blunts



Registered: 08/03/05
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Re: The Kilogram is Shrinking! [Re: demiu5]
#7425175 - 09/18/07 07:07 PM (16 years, 4 months ago) |
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Quote:
demius said: how does a fictitious unit of measure shrink?
Fictitious?
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DieCommie


Registered: 12/11/03
Posts: 29,258
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Re: The Kilogram is Shrinking! [Re: skydog]
#7425768 - 09/18/07 09:02 PM (16 years, 4 months ago) |
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I think he meant arbitrary...
In either case its a stupid question.
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DieCommie


Registered: 12/11/03
Posts: 29,258
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Quote:
"We could obviously use a better definition," Davis said.
Im surprised they havent redefied it yet with regards to some natural object (like has been done with c and the meter).
How about make the kg some multiple of electron's rest mass.
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maggotz


Registered: 06/24/06
Posts: 7,539
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Re: The Kilogram is Shrinking! [Re: DieCommie]
#7427136 - 09/19/07 07:27 AM (16 years, 4 months ago) |
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they're trying a bunch of methods to redefine the kilogram but apparently have had no success yet.
Quote:
A new approach to defining and realising the SI unit of mass (kg) is being explored.
Silicon crystal structure
It is possible to define the kilogram as a fixed number of atoms of a particular substance, thus relating the kilogram to an atomic mass. Silicon is a good candidate for this approach because it can be grown as a large single crystal, in a very pure form. For such an artefact, whose molar mass M and volume Vo of the unit cell (with n atoms) are known, the mass m of the crystal can be derived from a determination of its volume V if NA (the Avogadro constant) is known:
Mass of a crystal formula
i.e. m = mass of a single atom multiplied by the number of atoms present
The molar mass, unit cell volume and volume of the artefact can all be measured directly. However, the above equation can be re-arranged in terms of NA:
The Avogadro constant
i.e. NA = molar volume divided by the atomic volume
where is the density of the artefact and is calculated from its mass m (measured using the current definition) and volume V. This approach is therefore reduced to the problem of measuring NA with a relative uncertainty of 1 part in 108, which is equivalent to the uncertainty in the present definition of the kilogram.
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Seuss
Error: divide byzero


Registered: 04/27/01
Posts: 23,480
Loc: Caribbean
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Re: The Kilogram is Shrinking! [Re: maggotz]
#7427305 - 09/19/07 09:08 AM (16 years, 4 months ago) |
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Perhaps define mass in terms of gravity warp?
-------------------- Just another spore in the wind.
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maggotz


Registered: 06/24/06
Posts: 7,539
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Re: The Kilogram is Shrinking! [Re: Seuss]
#7427447 - 09/19/07 10:06 AM (16 years, 4 months ago) |
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there are two main types of experiments, the first is the avogadro project and the other one uses the watt balance. i'm pretty sure there are other experiments but i can't seem to remember what they were.
Quote:
This experiment measures a kilogram against the amount of magnetic force required to balance a 1-kilogram mass against the pull of Earth’s gravity. The experimental apparatus used to make the measurement is called a watt balance. A kilogram mass is placed on a balance plate that is surrounded by a coil of copper wire, which in turn is surrounded by a coil of superconducting wire. Magnetic fields produced by sending electricity through the coils push on the balance plate to offset the artifact's weight. The amount of electric current and its voltage then is used in defining a kilogram. Electrical power can be related to the Planck constant, defined as the ratio between the frequency of an electromagnetic particle such as a photon of light and its energy. This experimental method of defining the kilogram relies on selecting a fixed value for the Planck constant, which is currently determined experimentally based on the fixed value of the kilogram artifact.
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Seuss
Error: divide byzero


Registered: 04/27/01
Posts: 23,480
Loc: Caribbean
Last seen: 2 months, 20 days
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Re: The Kilogram is Shrinking! [Re: maggotz]
#7428111 - 09/19/07 01:14 PM (16 years, 4 months ago) |
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"against the pull of Earth’s gravity"
Unfortunately, the pull of Earth's gravity is not constant.
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maggotz


Registered: 06/24/06
Posts: 7,539
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Re: The Kilogram is Shrinking! [Re: Seuss]
#7428212 - 09/19/07 01:31 PM (16 years, 4 months ago) |
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trendal
J♠



Registered: 04/17/01
Posts: 20,815
Loc: Ontario, Canada
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Re: The Kilogram is Shrinking! [Re: maggotz]
#7428224 - 09/19/07 01:34 PM (16 years, 4 months ago) |
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I like the "Silicon crystal structure" idea the best, because it ties mass in the macroscopic world to mass in the atomic world the best (closest).
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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demiu5
humans, lol


Registered: 08/18/05
Posts: 43,948
Loc: the popcorn stadium
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Re: The Kilogram is Shrinking! [Re: DieCommie]
#7430079 - 09/19/07 09:13 PM (16 years, 4 months ago) |
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did we not 'invent' the kilogram? is it not 1000grams, which we also invented grams? are these not man-made measures, or am I missing something entirely here?
-------------------- channel your inner Larry David
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DieCommie


Registered: 12/11/03
Posts: 29,258
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Re: The Kilogram is Shrinking! [Re: demiu5]
#7430164 - 09/19/07 09:35 PM (16 years, 4 months ago) |
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.
Edited by DieCommie (11/12/16 11:14 PM)
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demiu5
humans, lol


Registered: 08/18/05
Posts: 43,948
Loc: the popcorn stadium
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Re: The Kilogram is Shrinking! [Re: DieCommie]
#7431220 - 09/20/07 06:13 AM (16 years, 4 months ago) |
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Quote:
What is happening is the standards that we pin our invention of the kilogram on are changing so they are no longer equal. Something is happening that we didnt predict, and is bad for standard measurements.
So, what myself and others on here have said is why not pin the invention of the kilogram on to something that is less likely to change, and more likely to remain a standard that future generations can reference. This can be done by defining the kg in terms of some atom or subatomic particle. This was done to the meter to make the standard less subject to change. Now the meter is defined to be 1/299792458 of the distance that light travels in one second (second being another of mans invented units, defined for a transition in a cesium atom). This leads to the speed of light being defined as 299792458 m/s. This is a good reference point because we always measure the speed of light the same, no matter where we are or how we are moving.
thanks for breaking that down; makes a little more sense now
-------------------- channel your inner Larry David
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