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The Changing Definition Of 'Kilogram'
DrLudicrous writes "The NYTimes is reporting that the platinum-iridium standard mass for the kilogram is shedding at an appreciable rate -- at least compared to other reference masses. The Pt-Ir cylinder is kept in France, and measured annually, and the slight discrepancy is important because the kg is an SI base unit- thus other quantities such as the Volt are based on it. A new standard is being sought- the two frontrunners are counting the number of atoms in a perfectly spherical single crystal of silicon, and another technique uses a device known as the Watt balance."
Hey I live in America you insensitive clod! (but then again I alawys want to know how much they are lifting on Strongman Competition).
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Everytime she steps on the scales...I would tell you what it was defined as last week, but kids may be reading this.
i'm not gaining weight, the kilogram is losing mass... so really, i stay the same weight, and they need more units to weigh me ;-)
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
Why couldn't they just take it down the shops and measure it against, say, 1kg of carrots or a kg of sugar?
Never fight naked, unless you're in prison...
Here is a site that gives some reasons why the are thinking of replacing the standard: http://physics.nist.gov/News/TechBeat/9501beat.htm l.
No registration necessary
The problem with the single crystal of silicon method, a few years ago, was that there were all these lattice vacany defects cropping up. The formation of such point vacancies is so entropically favoured that I don't think they can ever eliminate them...
My question is, how do they measure it? Using a non-decaying meter stick? How do you measure the definition of a measure?
I for one welcome our new SCOviet Russian overlords to whom all our base are belong.
Scientists Struggling to Make the Kilogram Right Again
By OTTO POHL
RAUNSCHWEIG, Germany -- In these girth-conscious times, even weight itself has weight issues. The kilogram is getting lighter, scientists say, sowing potential confusion over a range of scientific endeavor.
The kilogram is defined by a platinum-iridium cylinder, cast in England in 1889. No one knows why it is shedding weight, at least in comparison with other reference weights, but the change has spurred an international search for a more stable definition.
"It's certainly not helpful to have a standard that keeps changing," says Peter Becker, a scientist at the Federal Standards Laboratory here, an institution of 1,500 scientists dedicated entirely to improving the ability to measure things precisely.
Even the apparent change of 50 micrograms in the kilogram -- less than the weight of a grain of salt -- is enough to distort careful scientific calculations.
Dr. Becker is leading a team of international researchers seeking to redefine the kilogram as a number of atoms of a selected element. Other scientists, including researchers at the National Institute of Standards and Technology in Washington, are developing a competing technology to define the kilogram using a complex mechanism known as the watt balance.
The final recommendation will be made by the International Committee on Weights and Measures, a body created by international treaty in 1875. The agency guards the international reference kilogram and keeps it in a heavily guarded safe in a château outside Paris. It is visited once a year, under heavy security, by the only three people to have keys to the safe. The weight change has been noted on the occasions it has been removed for measurement.
"It's part ceremony and part obligation," Dr. Richard Davis, head of the mass section at the research arm of the international committee.
"You'd have to amend the treaty if you didn't do it this way."
That ceremony has become a little sorrowful as the guest of honor appears to be, on a microscopic level at least, wasting away.
The race is already well under way to determine a new standard, although at a measured pace, since creating reliable measurements is such painstaking work.
The kilogram is the only one of the seven base units of measurement that still retain its 19th-century definition. Over the years, scientists have redefined units like the meter (first based on the earth's circumference) and the second (conceived as a fraction of a day). The meter is now the distance light travels in one-299,792,458th of a second, and a second is the time it takes for a cesium atom to vibrate 9,192,631,770 times. Each can be measured with remarkable precision, and, equally important, can be reproduced anywhere.
The kilogram was conceived to be the mass of a liter of water, but accurately measuring a liter of water proved to be very difficult. Instead, an English goldsmith was hired to make a platinum-iridium cylinder that would be used to define the kilogram.
One reason the kilogram has lagged behind the other units is that there has been no immediate practical benefit to increasing its precision. Nonetheless, the drift in the kilogram's weight carries over to other measurements. The volt, for example, is defined in terms of the kilogram, so a stable kilogram definition will allow the volt to be tied more closely to the base units of measure.
A total of 80 copies of the reference kilogram have been created and distributed to signatories of the metric treaty. The sometimes colorful history of these small metal cylinders underscores how long the world has used the same definition of the kilogram.
Some of the metal plugs were issued to countries that later vanished, including Serbia and the Dutch East Indies. The Japanese had to surrender theirs after World War II. Germany has acquired several weights, including the one issued to Bavaria in 1889 and the one that belonge
Since there is only one reference object for the kilogram, everything else is just a copy -- and even if it is a first generation copy, errors are bound to creep in.
The redefinition of the kg is long overdue, mad props to the scientists working on this.
nah .. they should throw out the whole kilogram concept and weigh everything according to a "library of congress".
eg. that woman weighes 2.36 libraries of congress.
One nominee that is amusing is to have the basic unit of distance based on the speed of light.
One light nanosecond = roughly 11.1 inches, kinda close to a foot.
I remember how Grace Hooper used to pass out wires that were that long, just to make the point.
Any other nominees?
"It is a greater offense to steal men's labor, than their clothes"
And all this time I just thought I was just getting used to cocaine.
Darn right! After all, it's easy enough to convert fortnights to stone with a Mayan calendar.
We're going to in the future eventually. It's inevitable.
I know it's 60 firesticks per 100 Watts, and 3000 Volts per staticy tomcat, but it might just be easier if we all just jumped in and switched to metric 144%.
I mean picture doing 100 on the highway! Wouldn't that be great? And dozens of future Mars landers would actually land on Mars, instead of digging ideal tree planting holes and landscaping future martian neighbourhoods. ("Zyphod! Incoming! It's the Americans!")
No more two sets of wrenches and lost sockets! Now you can have one set of sockets with half the sockets missing, instead of two sets of sockets with half the sockets missing. And no more asking for an 5mm and trying to make a 1 3/4" fit, rounding off the edges and carving a perfect turkey slice off your hand and gushing gallons of blood. It would be litres, which is less.
And you get to tell women that you, sir, are endowed with twenty-two centimeters of man!
Of course, the loss of the 25 cent piece will be a negative, since we'll have to pay for everything in dimes. But it's worth it dammit.
Seriously, we all know this is going to happen. When are we on board? Are we that stubborn?
The baby's fine -- please stop sending business cards.
It doesn't exactly have to be measured. They just do that to check it's still right. Go read about the history of the Systeme International the NIST site and the definition of a kilogram at the same place
But essentially, its part of a way of ensuring that the measuring units Scientists use around the world are the same, not slightly different.
For instance, anyone around the world can reproduce (in a well equipped lab anyway) the definition for time (The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom).
There are only 7 base SI units (meter, kilogram, second, ampere, kelvin, and candela) from which many more units are derived. Hence, if kilo is out/changing many of these are changing too.
and why should I care if it detoritates?
Presuming you're American, you would use feet, pounds, find metric too complicated, etc, etc - so probably wont care if it does.
The unit of "volt" can also be expressed as m^2kgs^-3A^-1.
Karma: Terrifying (mostly affected by atrocities you've committed)
It's not the arbitrariness, but the fact that metric is a decimal system.
The only countries left that don't use metric are the US and Bhutan. Bhutan is a fundamentalist islamic country that doesn't even have any phones yet. I guess we can see what the US' technical level is.
One kilogram is equal to the weight of 1/256th of a VW beetle! Simple as that! Silly French.
Is there any physical reason (other than that small matter of cost ) that crafting a new kilogram (or more likely, gram) out of diamond would not be an ideal solution?
BTW, theNational Physical Institute has a FAQ on its Pl-Ir standard kilo.
The only known quantity of Unobtainium (UB238) has gone missing.
The 1 kilo square block was being held in Brussels awaiting return to Brazil, where it was originally unearthed.
It was determined that the physical stability of the material was being affected by being moved from it's original location, that of being south of the equator. Investigators are anxious to reclaim the material in hopes of stabalizing it's rumored flux in mass. The UB238 was being packaged for transit, when it suddenly dissapeared from the shipping room counter. The rumor that it had created, and subsequently fallen into, a 'portable black hole' was discounted by investigators on the scene.
Once the Unobtainium is recovered, and returned to Brazil, it can be weighed and certified as a replacement for the Pt-Ir cylinder that is kept in France, and measured annually, representing the kilo standard for the world.
MPEG at 11.
It seems they should just reference the kilogram to a standard, such as x,xxx,xxx,xxx Si (28 isotope) atoms. This would eliminate the complications trying to build a standard, duplicate it and correct for earth's gravitational variations at the time and place of checking physical reference mass (not weight, to which the article alluded). Keep in mind the kilogram is a measure of mass, and not weight. That is why maintaining a physical standard requires correcting for gravity at the location's, time, elevation, tide, (add geophysical conditions, ad nauseum) of measurement.
If we are maintaing a physical chunk of alloy as the standard, it's time to decide on a more precise measurement, like we did with the meter long ago.
The various prefixes -- kilo, Mega, Giga, and so on -- are very precisely defined SI prefixes that have been in common use in the sciences for quite some time now. In computing though, 1024 bytes was originally termed a "kilobyte" because it was very close to an actual "kilo" of bytes (1000 bytes), and so was a convenient term to use. In other computer-related disciplines though, in particular engineering, the correct SI usage prevailed, so your 128 kbps mp3s actually have 128000 bits per second, not 128 * 1024.
The big problem is that 2^(10x) and 10^(3x) diverge as x increases: 1024 is 2.4% more than 1000, 1048576 is 4.9% more than 1000000, 1073741824 is 7.4% more than 1000000000, and so on. So obviously the "close enough" thing is getting less and less true -- when there's a 10% difference between the two measurements they're not even close enough for everyday colloquial speech.
So the solution of both the SI and the IEEE is to reassert the original meanings of the SI prefixes (kilo = 1000, Mega = 1000000, etc.), but to add new base-2 prefixes in recognition of their usefulness in computing. These are kibi, Mebi, Gibi, etc. (basically the same as the SI prefixes but with the last two letters replaced by "bi"). Their standard abbreviations are the same as for the SI prefixes, but with a lowercase 'i' appended (so ki, Mi, Gi, etc.).
The conversion is obviously nowhere near complete, and irritates some computer people who don't want to change the terms we've been using for decades, but this seems to be the only really reasonable way of doing things. The only other two options are to either force the rest of the sciences to change to use the base-2 definitions (which is obviously not going to happen, and they got there first anyway), or to maintain the current ambiguity, which is also obviously undesirable.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
I believe bhutan is a buddhist/hindu country.
What i've never understood is since the kilogram is the base unit why didn't they just call it the gram?
I can't reveal its identity for this precise reason.
Yes - there is a mole in the base S.I. units - but I can't tell you it's name. Its been on a secret long term sleeper mission - to liberate the S.I. units and term them into "Freedom Units"
c is a constant, of course. In fact, it's used to define the meter as how far light travels in a vacuum in 1/(299,792,458) of a second. Second is defined as the time for a certain number of vibrations of a Cesium atom to occur. As per your question of relating mass to Joules, note that high-energy physicists do this all the time. They usually refer to masses of particles as MeV/c^2. And they usually work in units where c=hbar=1, thereby making distance, time, and energy all essentially the same units (easier to do calculatins that way).
One thought that jumps to mind for a standard energy interval is the lyman alpha energy width (the jump of the electron in a hydrogen atom from n=2 to n=1 where n is the energy quantum number). Or, for mass, use a standard mass of a well-defined particle such as an electron. In fact, I'm surprised that NIST doesn't do this. It might be that isolating electrons for mass measurements are too difficult (gravity is weak), but electron mass does show up in many other calculations (specific heat of degenerate electron gases, for instance). Or isolating ultra-pure hydrogen gas and spectroscopically measuring Lyman alpha is more difficult than it seems. I guess NIST wants [relatively] easy methods for measuring these quantities.
Okay, I just found this site which answers the question. They quote
It all boils down to ability to measure the standard units to the highest precision possible. I'm actually stunned that the mass of that bar can be weighed to that precision.
As a side note, if you can come up with a better way of measuring fundamental constants, you might win a Nobel Prize. The guys that discovered the integer quantum hall effect initially published their results as a better way to measure some of the fundamental constants.
make world, not war
The posted article, while interesting, is wrong about the volt being based on the Kilogram. Since about 1990, the volt is defined to be the voltage applied to a Josephson junction that produces a frequency of 483,597.9 GHz. This new standard was implemented in order to get away from relying on 'artifact' standards (such as the Kg cylinder). One quick source page on Josephson junctions (which completely revolutionized the field of Metrology back when I was a calibration tech in the AF) is:/ squid.html
http://hyperphysics.phy-astr.gsu.edu/hbase/solids
If I recall correctly, the eventual goal of the international standards organization was to find ways to define everything in terms of frequency/time since we can measure time so accurately/precisely.
So I now weigh 75kg...give or take a bit :o
Wait till I tell my fiance that her weight
fluctuates on a weekly basis!
These pseudoscience concepts are getting out of hand.
I don't think we need "feel-good" physics.
Now they want to base a standard on a crystal ball?
a kilogram is, however, a measure of mass, not weight. it is therefore unaffected (if properly measured) by the force of gravity.
I've been waiting a while to tell my high school chemistry teacher that a Kilo is 1024 of anything, and I do deserve that A. ~JM
Hmm, so instead of a year being 365 days long you would want it to be 456 days long? (365 days * 1.25 = 465 days)
A leap year has nothing to do with anyone screwing up. The problem is that a year does not have an integral number of days. A year is 365 days, 5 hours, 49 minutes (365.2424 Universal days)*. That means that it takes about 526,297 minutes for the Earth to make a full trip around the sun. After the Earth has rotated about its axis 365 times it will still take about 350 minutes until it reaches the same spot it started from.
That means that if you tried to have the year be an even number of days, say 365, you would fall behind almost 1 full day every 4 years. It's not much but if you let it go for a while you will start having winter during the hottest times of the year. There are a few other rules that adjust the calendar besides the "extra day every 4 years" rule and because of these rules we are able to keep the seasons approximately where they should be.
To learn more about how the calandars were changed visit this web site.
*source: Timeline of interesting calendar facts
Sapere aude!
Fundamentalist Islamic country without any telephones?
Can I have some of whatever your smoking please?
More than mere navel gazing.
"'It's certainly not helpful to have a standard that keeps changing,' says Peter Becker, a scientist at the Federal Standards Laboratory..."
Wow, someone should tell the computer industry that.
"Some of the metal plugs were issued to countries that later vanished, including Serbia and the Dutch East Indies. The Japanese had to surrender theirs after World War II. Germany has acquired several weights, including the one issued to Bavaria in 1889 and the one that belonged to East Germany."
SURRENDER YOUR KILOGRAM!
The same deal with Plack's constat. It's value is not up to us, but up to nature. "Defining" it would be like defining pi as 3.
A year is 365 days, 5 hours, 49 minutes (365.2424 Universal days)
Why don't we just get a big rocket, and alter the orbit so that it is exactly 365 days ? Or better yet 366 days, then we can give everyone a holiday (in rememberance of all of the species that were extinguished for our selfish ends).
In Soviet America the banks rob you!
Except that no one has actually counted/created a structure composed of a mol of any particular element.
The minute you can do that, then you can reliably and predictably create a fixed metric by which any one in any place can measure mass.
GPL Deconstructed
A kilogram is the measurement of a certain amount of matter, not it's weight. Sure the two are related, but not the same.
A kilogram is the same on the surface of the earth, in outer space, or one the moon. Weight however, varies with gravitational pull or acdeleration.
In other words, weight is basically the mass of on object multiplied by whatever gravitational field you happen to be in.
The kilo shall be defined to be 1/80 of my weight. In return for the honor I promis to make the worlds people slim down.
Trolling is a art!
Just to confuse the matter more, in the 1970s, it was common to use metric sizes of threaded copper pipe, which had external diameters in sizes approximating common fractions of inches: 13mm = 1/2", 16mm = 5/8" and 19mm = 3/4" just to mention some of them. These appearently were all threaded with 1mm pitch threads.
Later, these were replaced by true metric pipe sizes with compression fittings or capillary solder fittings. Now the sizes changed again, common ones are 8, 10, 12, 15, 18, 22, and 28 mm. And of course, one needed compression fittings made for 16mm and 19mm also, so as to fit the older pipes...
That's Europe. What I have seen in the US are the commonly found so-called 1/2" copper pipes with solder fittings, this is about 16mm (5/8") in diameter, so I guess they are still using internal diameter measurements. Similarly, the so-called 3/4" pipes appear to have about 21mm outside diameter.
I guess the easiest way to turn these into metric sizes would be to redefine them as 16mm and 21mm and leave it at that. At least the traditional inch-units pipe thread sizes are roughly the same everywhere!
SIGBUS @ NO-07.308
he kilogram is shedding at an appreciable rate
you mean I'm actually losing weight without doing diets or a workout !!
And the metre is defined properly these days (as is the second) in terms of wavelengths of radiation.
No. In SI units, c is not measured but defined. Physically, c is just a man-made constant of proportionality deriving from the fact that, for historical reasons, we measure time differently from space. In reality, both time and space are physical dimensions and so it makes perfect sense to express both in terms of the same units, be they seconds or metres.
That's why most theoretical physicists like to do their calculations in "natural units" -- i.e. you set c=1 and h/2pi=1 -- since in reality the values of the fundamental constants are artefacts of your measurement system. Scientifically speaking, it makes sense to set all independent constants to 1 since it brings out the fact that the "equivalence" of eg mass and energy, or distance and time, is really an identicality.
The author of this post asserts his moral rights.
The standard 1 kg block should be replaced by the 1 kg Christmas Fruit Cake. As everyone knows, it is indestructible, and only one exists in the entire world (people just keep mailing it around to each other every year).
---- ---- --- -- --- ------ Keep Cool But Do Not Freeze
Just as a minor correction ... the volt is no longer defined in terms of the kg. The international definition of 1 Volt is now defined in terms of the "Josephson Effect" and is an effect observed in superconducting materials that are interupted by a normal metal.
It turns out, that even without an applied voltage, there is still a current in the system, and after a voltage is applied, the current oscillates at a very predicable rate. Thus, the volt is now defined as the potential required to give a specific number of current osciallations in a Josephson Junction.
Nit-pickey I know, but maybe of interest.
The watt balance solution seems to be linking the Kilogram (mass) with force (weight). This is not entirely desirable, since something that masses a kilo on earth will still mass a kilo in space, or on the moon, or on jupiter. It's mass doesn't change, only it's weight. The Watt balance then, would not only be impractical (imagine having to construct a "3-story structure" every time you want to accurately weight something?), but downright useless for many aerospace applications. Any system of measurement that's dependant on the phase of the moon for it's accuracy should immediately be discounted, in my opinion...
I am alone, yet I also surf the universal backwash of undifferentiated Being, which is LOVE.