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  • OT - Kilo prototype mysteriously loses weight

    Thought you might find this interesting...

    TMT

    http://news.yahoo.com/s/ap/20070912/...MYIDpZcsZn.3QA


    Kilo prototype mysteriously loses weight By JAMEY KEATEN, Associated Press Writer
    Wed Sep 12

    A kilogram just isn't what it used to be.

    The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly. 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.

  • #2
    It probably really hasn't lost any weight. The others just have fingerprints on them.
    .
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

    Comment


    • #3
      What kind of material is it made out of --- It either didnt say or i missed it, im sure certain materials would matter, then again thier leaving this all up to the french? wut up wit dat?

      Comment


      • #4
        Originally posted by Too_Many_Tools

        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.
        I believe they mentioned it.

        Makes you wonder what it would have weighed if they machined it to metric rather than imperial dimensions though.
        .
        "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

        Comment


        • #5
          maybe someone breathed on one before measuring it,seriously maybe they didnt have the precision tools for measuring we have today Alistair
          Please excuse my typing as I have a form of parkinsons disease

          Comment


          • #6
            I think the article says that they compare them on a regular basis so they must be seeing some consistent drift, improvements in measurement notwithstanding.

            Perhaps like Mae West - "I used to be Snow White, but I drifted." Who knows what those things are doing in the dark when they're not out being measured.
            .
            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

            Comment


            • #7
              Originally posted by TGTool
              Makes you wonder what it would have weighed if they machined it to metric rather than imperial dimensions though.
              It wouldn't matter what its physical dimensions are, it would still weigh a kilogram. That's the problem - it has lost or gained mass, not really known, but no matter, it still weighs a kilogram. If it lost half its mass it would still weigh a kilogram. When you grab the kilogram standard down off the shelf and put it on a scale you have to adjust the scale until it reads one kg. A quandry? Sure. A paradox? Not really. A problem? Of course.

              Comment


              • #8
                Rats??

                Maybe a Big Rats Gnawin on it ??

                Comment


                • #9
                  This just illustrates the need to move to natural constants for our standards. They already did it with the two most important ones, time and length, and now the remaining prototype standards just have to follow suit.

                  Our measurement apparatuses are plenty accurate, but they aren't constant. Like back when Kr-86 was the standard for length. Interferometers were capable of higher resolution than the Kr-86 source, but there's drift over time in an interferometer, and they have to be referenced back against a primary standard periodically. The Kr-86 is stable forever, but you can't measure it all that accurately. Mass and force are the same way.

                  The big problem, like many people have already posted, is that you can't know with any absolute certainty what is going on. You don't have any standard unit, so all you can do is use comparative devices. Like comparing two parts with a dial test indicator with arbitrary graduations; if you don't have a gage block stack as a reference, all you can say is "hey, this one is less big than this one."

                  I've seen pictures of the kilo prototype and the vault, and believe me, there aren't any fingerprints or rats gnawing on the thing.

                  Comment


                  • #10
                    maybe dark matter is sticking to the rest of them. since you can't see it, how would you know it's there?

                    andy b.
                    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

                    Comment


                    • #11
                      Originally posted by toastydeath
                      This just illustrates the need to move to natural constants for our standards. They already did it with the two most important ones, time and length, and now the remaining prototype standards just have to follow suit.

                      Toasty,
                      At the National Institute of Standards and Technology in Gaithersburg, MD, they have been working on this issue for years. One, the Electronic Kilogram, is especially interesting.

                      To give you an idea of the level of accuracy they are measuring/comparing mass, the scientists there can sense changes in the mass of the Kg with variations of temperature and humidity as these conditions change the buoyancy of the air. The Kg mass at NIST is kept in a room whose air temperature is controlled to +/-0.01C and +/-1% RH to help negate the effect.

                      In another lab, they are using a smaller version of the electronic Kg to measure the force needed to pull a single atom from the surface of a test sample.

                      See this link to an article on the E-Kg
                      http://www.eeel.nist.gov/817/news/pr...rokilogram.htm

                      and this link to other efforts to redefine the Kilogram. (including a perfect sphere of crystaline silicone.)
                      http://www.nist.gov/public_affairs/n...f_kilogram.htm

                      Enjoy the articles,
                      Todd.
                      Todd Snouffer
                      Littlelocos Model Engineering
                      www.LittleLocos.com

                      Comment


                      • #12
                        So, what do you replace a mass standard with except another mass standard? BTW, 50 micrograms is a lot. One of the meds I take has a starting dose of 125 micrograms. That's an easy amount to measure.

                        I think that some sort contamination was present when the masses were originally compared and has been evaporating slowly since. I bet if they look at the materials used to clean it that they will find that those materials have become more pure over the years and that some unsuspected impurity used to be present in greater quantity than it is now. Perhaps something like a minute trace of an oil or wax dissolved in the solvents used to clean the artifact was left behind after cleaning. If that is the case it will be very difficult to verify unless they still have some samples of the earlier cleaning solutions.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          You replace the mass standard with a value that can be experimentally determined using universal constants.

                          For example:

                          The second is some ridiculous number of hyperfine level oscillations in a cesium-133 atom in its ground state. That's going to be the same anywhere, and anyone who really wants to can generate their own primary time standard can do so. There's no reliance on some artifact for accuracy, and your resolution of the second is limited only by your resolution in the experiment.

                          Same with distance. The meter is some fraction of the distance light travels in one second, which works out to some number of wavelengths of light at some frequency, which can be directly measured by an interferometer to a very close value. Again, no physical standard is necessary and can be reproduced by anyone with enough time and money on their hands.

                          Comment


                          • #14
                            Originally posted by Evan
                            So, what do you replace a mass standard with except another mass standard? BTW, 50 micrograms is a lot.
                            ... two contenders are combinations of well-known electrical standards and counting the number of silicon atoms in an artifact grown an atom at a time. Both of these are described in the links above.

                            I am pretty sure the AP article is misquoting the dimension. 50 micrograms is HUGE at the level they are talking about.

                            This seems to be a better article. It focuses on the work being done at NPL in Great Britain. (although it gives the drift rate at 50 milligrams per century, ...argh)

                            http://pubs.acs.org/cen/science/83/8329sci1.html


                            Todd.
                            Todd Snouffer
                            Littlelocos Model Engineering
                            www.LittleLocos.com

                            Comment


                            • #15
                              Originally posted by toastydeath
                              This just illustrates the need to move to natural constants for our standards. They already did it with the two most important ones, time and length, and now the remaining prototype standards just have to follow suit.

                              Our measurement apparatuses are plenty accurate, but they aren't constant. Like back when Kr-86 was the standard for length. Interferometers were capable of higher resolution than the Kr-86 source, but there's drift over time in an interferometer, and they have to be referenced back against a primary standard periodically. The Kr-86 is stable forever, but you can't measure it all that accurately. Mass and force are the same way.

                              The big problem, like many people have already posted, is that you can't know with any absolute certainty what is going on. You don't have any standard unit, so all you can do is use comparative devices. Like comparing two parts with a dial test indicator with arbitrary graduations; if you don't have a gage block stack as a reference, all you can say is "hey, this one is less big than this one."

                              I've seen pictures of the kilo prototype and the vault, and believe me, there aren't any fingerprints or rats gnawing on the thing.

                              The link I supplied has a photo of the standard.

                              TMT

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