From the Wall Street Journal – By JEANNE WHALEN
In a vault beneath a 17th-century pavilion on the outskirts of Paris sits a platinum cylinder known as Le Grand K. Since 1889 it has been the international prototype for the kilogram, the standard against which all other kilos are measured.
But over the years, scientists have noticed a problem: Le Grand K has been losing weight. Weigh-ins at the International Bureau of Weights and Measures show that the bar has shed approximately 50 micrograms—roughly equal to a grain of sand.
The problem has vexed scientists who monitor the kilo the way tabloids track the waistlines of Valerie Bertinelli and Kirstie Alley. The stakes, however, are weightier.
“It’s a scandal that we’ve got this kilogram hanging around changing its mass and therefore changing the mass of everything else in the universe!” Bill Phillips, a Nobel Prize winning physicist, exclaimed at a scientific summit in London this week. No one knows for sure what went wrong with Le Grand K, but some theorize it lost weight from being cleaned.
Dr. Phillips and other mandarins of metrology were gathered at Britain’s Royal Society to debate an urgent question in the science of measurement—how to re-define the basic unit of mass, as well as other measurements such as the second, ampere, kelvin and mole.
The aim is to tie each to a widely accepted property of nature, rather than to a lump of metal or some other imprecise benchmark. The meter, for instance, was once measured as the distance between two notches on a metal bar. It is now defined as the distance light travels in a vacuum in 1/299,792,458 of a second.
The new definitions are “as big a change as the introduction of the metric system during the French Revolution,” says Terry Quinn, a dapper Briton who organized the seminar and once served as director of the International Bureau of Weights and Measures, which ensures world-wide uniformity of measurements. Frequent clashes about the best approach mean the temperature of debate has at times “risen quite high,” he added, without specifying by how much.
Full story at the Wall Street Journal
If the metric system was really so great and easy to understand, users would say something weighs so many Newtons.
When we say how many pounds something weighs, at least we’re using the correct units for the system. ☺
>>>>Enchamp… The moral of this little tale is, I suppose, that you should always check your units of measurement. Failure to do so could result in either a very costly plant shut-down, or an explosion.
Or a Boeing 767 to run out of fuel in midflight…. Anyone here remember the Gimli Glider incident in 1983?
http://en.wikipedia.org/wiki/Gimli_Glider
It used to be, 40 years ago, that the kilogram was defined (in school) as the mass of one liter of H20 at STP. One liter being defined as the volume created by a 10 centimeter cube and one centimeter as 1/100,000,000 of 1/4 the Earth’s diameter.
The origins of the meter go back to at least the 18th century. At that time, there were two competing approaches to the definition of a standard unit of length. Some suggested defining the meter as the length of a pendulum having a half-period of one second; others suggested defining the meter as one ten-millionth of the length of the earth’s meridian along a quadrant (one fourth the circumference of the earth). In 1791, soon after the French Revolution, the French Academy of Sciences chose the meridian definition over the pendulum definition because the force of gravity varies slightly over the surface of the earth, affecting the period of the pendulum.
Thus, the meter was intended to equal 10-7 or one ten-millionth of the length of the meridian through Paris from pole to the equator. However, the first prototype was short by 0.2 millimeters because researchers miscalculated the flattening of the earth due to its rotation. http://physics.nist.gov/cuu/Units/meter.html
The whole point of the kilogram was that is was unit of MASS not weight. The problem is gravity changes over time and from place to place, so any 50 mircograms of change/weight could easily be accounted for on Earth a change in gravity. You can claim all day long that you are measuring mass BUT on earth you are weighing something in a gravity field and I don’t care how fancy your equipment is or what technobabble you come up with you are still WEIGHING the object even IF it is against a reference mass.
This is a tempest in a teapot. Stick with what you got and go with it otherwise all your previous measurements are worthless. You do know there is such a thing as significant digits and we used that math concept with sliderules to get to the moon.
Slightly off Topic but I have to share…
I told my 8 year old that we will be getting a foot of snow on Tuesday. He looked at me with a serious face and asked “My foot or your foot”.
Long live man-defined-measurement. If a meter is the distance light travels in a vacuum in 1/299,792,458 of a second. One has to ask how accurate is a second?
Every measurement compares an ‘unknown’ with a ‘reference’ (even if it is your thumb); so fundamental mass measurement always involves a ‘beam balance’ comparator, with two pans and a central pivot to compare two Pt-Ir cylinders. Visit the BIPM website to see just how carefully they do it with le Grand K.
2. The BIPM website gives a very full description (with colour photographs) of the ‘cleaning process’ applied to every pair of prototype Pt-Ir ‘std’ kilogram masses before any two of them are compared with each other.
3. Changes due to cleaning are obvious candidates for observed ‘variations’ in the differences between any selected pair of ‘std’ 1.000000±0.000025 kg masses over any 40 year period. Gravity is not, because, by definition, a beam-balance comparison places the compared masses at the same place and time when each comparison is made.
For crying out loud, it’s only 50 micrograms in 1000 grams, over 100 years, and of no practical significance in any actual measurement program anywhere in the world. It’s not a serious problem! [Not like trying to cut 0.01 C per CENTURY off the average slope of a temperature anomaly calculation, based on dubious quality temperature measurements].
Merovign has evidently not ever had someone give him moment of inertia, variously, using ounces of force, ounces of mass, lbs of force, lbs of mass, and distances in feet or inches, depending on who it was and how they felt on a given day.
Occasionally you see mass given in slugs. But that’s rare. In my decades-long conversion to metric aficionado, I can count the number of times I’ve seen Newtons used as a unit of force on the toes of my hind feet.
I’d want to know more about how they’re measuring mass before I started jumping to conclusions, here.
“”””” Smokey says:
January 28, 2011 at 5:08 pm
Measuring mass at the microgram level is much more difficult than it would seem. Mass is often confused with weight, but they are not the same. “””””
Prior to the two most recent America’s Cup contests, a series of pre-events were held to keep sailor, and team sponsor interests alive and gather points towards deciding the Challenger to the then current Cup holder; Swiss Alinghi Team.
The first Regatta was held an the Mediterranean off Spain.
Part of qualifying the boats, involved verifying the wieght of the boats. Teams wanted to run their boat up to the maximum weight limit, to have available the maximum righting moment from the lead keel bulb.
Following that regatta, the next set of qualifying races was set for Malmo, in Sweden (snake eyes over the ‘o’ ); which happens to be at 58 deg 21′ North latitude, so it is far enough North to be major affected by the oblateness of the earth, so (g) is higher in Malmo.
Every single boat in the fleet failed the weight limit remeasure. The dummies that wrote the roolz, specified the Weight limit for the boats, rather than specifying a Mass limit. Don’t remember how they resolved the fox pass; whether they waved the transgressiosn, or made everybody cut a piece off their boat.
Emirates, Team New Zealand, ended up challenging the Swiss for the cup, and sort of blew a contest they should have won; but a successful defence to the Alinghi Team.
“”””” V in PA says:
January 31, 2011 at 6:24 am
Slightly off Topic but I have to share…
I told my 8 year old that we will be getting a foot of snow on Tuesday. He looked at me with a serious face and asked “My foot or your foot”.
Long live man-defined-measurement. If a meter is the distance light travels in a vacuum in 1/299,792,458 of a second. One has to ask how accurate is a second? “””””
The definition just given means that (c) is 2.99792458 x 10^8 m/s
That number is exact by definition. The second is defined in terms of the frequency of the emission due to a specific transition in 133Cs; specifically between the hyperfine structure levels of the Ground State; which is 9,192,631,770 periods at that frequency. It is considered accurate to a part in 10^14, which is good enough for most sports events.
Since (c) = 1/sqrt(mu_nought x epsilon_nought); and mu_nought is 4pi x 10^-7 V.s/A.m (Volt. sec/Amp. metre) which is exact; then epsilon_nought = 8.85418781762 x 10^-12 A.s/V.m must also be exact (and is).
It used to be that the second was defined in terms of the frequency of one spectral line (as now) and the metre was defined in terms of the wavelength of another spectral line ( in 86Kr I think), so (c) was dependent on a comparison of those two lines.
But now (c) and the electric constants which give (c) from Maxwell’s equations, are defined exactly.
“”””” dscott says:
January 30, 2011 at 8:01 pm
………………..
The whole point of the kilogram was that is was unit of MASS not weight. The problem is gravity changes over time and from place to place, so any 50 mircograms of change/weight could easily be accounted for on Earth a change in gravity. You can claim all day long that you are measuring mass BUT on earth you are weighing something in a gravity field and I don’t care how fancy your equipment is or what technobabble you come up with you are still WEIGHING the object even IF it is against a reference mass. “””””
Well actually you are comparing the gravitational attraction between the earth and each of the standard mass, and the test mass. Yes it is true that if you do this with a beam balance, the two masses are in different places in that “gravitational field” you mentioned. That problem is trivially solved by providing an electromagnetic field to cancel the weight of the standard mass, and then swapping the two masses, and comparing the EM field comparison. So now the two masses are in exactly the same gravitational field, and the em field can be set in the same center of mass location in that field.
Weight unfortunately is not a very good measure; well just the sloshing around of the oceans, must perturb the weight due to varying accelerations of water masses.
I have “weighed” the entire earth myself; and it typically runs in the range of 180 pounds avoirdupois. You can do it yourself; but you likely will get a different answer from mine.
You need a plane mirror, and a stout bucket or footstool; well you also need a bathroom scale to weigh the earth on.
So you put the plane mirror on the floor face up, alongside the footstool or bucket (upturned); and then you place the bathroom scale on top of the footstool; upside down so you can read the scale in the mirror. When I do this I get some totally chicken**** weight for the earth of about 2-3 pounds.
So then I climb up and stand on top of the upsidedown scale, to add some stability to the system, and peer over the edge with my computer glasses on so I can read the scale upside down. Right now it reads about 177 pounds; but more often, than not, it reads 182 pounds.
The weight of the earth is highly variable, and not something you can depend on for anything.
“”””” Alexej Buergin says:
January 29, 2011 at 11:23 am
I have yet to meet an American who can tell me
1) how many feet to a mile
2) how many square-feet to an acre
3) what a pound is, and what is measured by it
4) how many Watts in a horsepower
5) the unit one measures blood pressure in
All very simple if you know metric. “””””
Well Alexei; I’m an American, and without googling or yahooing, or wikipiddling, I can guess the following answers to your questions:-
#1 5280 ft per mile.
#2 43560 squ ft per acre, or 4840 squ yds if you like.
#3 As they say; “a pint of water weighs a pound and a quarter”, except in the USA, where they say; “a pint’s a pound, the world around.” which of course it isn’t at all. And it measures both the mass and the weight of a body under the assumption of a standard acceleration due to gravity (g) of 9.80665 m/s^2, which I believe is the value accepted for sea level at about +45 deg North Latitude. Various conventions would dictate using “pound” if referring to mass, and “pound weight, if meaning the weight of a pound (mass). Then one could mention the “poundal” which would be defined loosely by saying the weight of one pound (mass) is (g) poundals.
#4 a horsepower is 746 Watts.
There is of course the Troy Ounce used in precious metals, and jewellery; but I have never seen anybody’s definition of a Troy Pound; or even if there is such a thing.
#5
Now I don’t know diddley squat about the units for blood pressure; all I know is that my units are different from everybody elses; and they roam all over the map. My doctors think I am a transitionary specimen somewhere in the gap between homo sapiens sapiens; and whatever species we are evolving into; they also say it isn’t a problem; just abnormal.
But now Alexei; I would like to trump your ace.
Please explain to us; slowly if you will, since some of us are quite dense;
Exactly how does “knowing the metric system” enable one to computet “the number of square feet in an acre” ?
From Alexej Buergin on January 29, 2011 at 11:23 am:
Millimeters of mercury, mmHg, with 1 mmHg approximately equal to 1 Torr, which is defined as 1/760 of an Atmosphere (atm). It is a rather unscientific unit, deserving of ridicule. From the Wikipedia Torr entry:
Pounds per square inch (psi) is a far more scientifically valid unit.
Chris Reeve says:
January 30, 2011 at 11:28 am
Re: “Whenever proponents of any theory, however ridiculous, are censored out from any forum, I feel bad aftertaste.”
To some extent, I perhaps have to apologize for being too specific and wordy in my attempt to talk about mass and gravity on this climate blog. In this regard, my post was inappropriate.
———————————————————————————–
Chris:
Think twice before bringing up your theory. There was a guy on here once who was warned many times, about his pet ‘Iron Sun’ theory. It would show up in dicussions about why French officers wear brown pants(so their felllow officers don’t see them panicking!!!). He would inject it into every discussion if (usually only) he felt it was remotely relevant. He couldn’t help himself. I’ve seen the Electric Universe discussed here at WUWT ad bbc2(can’t spell neuseum!). Your chance will come….again….and again and you’ve discussed it before. When it’s patently related to the subject, you’ll have no problems. A life time ban stares you in the face.
because you are not listening.
Anthony doesn’t have time to keep repeating himself. I’d go back through the archives and see all of Leif’s responses to all the EU stuff. And figure out how better to present the ideas more convincingly. Some data would help too.
Fair warning?
As for the French: can’t they do anything without taxing it!
Somewhere around early 1990 an intern cleaned the standard with ordinary paper towels.
He was the boss’s nephew so it was kept quiet.
They didn’t think anyone would notice a few scratches.
The intern, later that year worked as a janitor at NASA on the hubble telescope project. 😛
My instinct says it is from the “Hydrogen in Metals” effect. The Hydrogen might be acting as a solvent.
Platinum is exactly the class of metals that is subject to this phenomenon, along with Palladium.
Metallic suboxides dissolve Hydrogen, but that means the metal is being affected, too. At least I think so.
I am amazed at how many people commenting here have talked about the accuracy of the measuring or metrology itself (even to screw threads!). I am sure that the measuring itself is the first thing the IBWM looked at and wouldn’t be outing this problem without eliminating other possibilities (as opposed to AGW fans, for example).
Tim Folkerts January 28, 2011 at 7:46 pm:
Actually, I believe it was a litre of water at 4°C. And I am pretty sure the litre of water was defined as 1,000ccs, which themselves were defined as 1,000 drops of water at 4°C. As such, the liter was not a volume, but a number of drops of water. At least that is what I recall.
Engchamp January 29, 2011 at 2:20 pm:
If by “we” you mean in the U.S., having worked in mechanical engineering for 39 years, I can tell you BSP is not enduring in any companies I’ve ever worked with, threaded pipe with BSP threads is quite uncommon. NPT (National Pipe Thread) is the U.S. standard.
Also wrong. The U.S. does, in fact, have two pitches. The standard in the U.S. is Unified Threads, and screws and nuts come in both UNC and UNF – Coarse and Fine – and both are very available in every hardware store and supply house.