The Kilogram Is Losing Weight And That Might Screw The Metric System

We've long known that there were some issues with France's 'Le Grand K', the international prototype for what a kilogram really is. Made in 1879 from platinum and iridium alloy, it is the perfect standard for what a kilogram weighs. The problem is it's losing weight.

Mental Floss takes a look at what the lost weight of the official kilogram means and the flaws of using a physical standard for such important purposes — it's all so fascinating. For example, scientists are scrambling to redefine what a kilogram is like how they changed the definition of a meter from once being a metal rod stored next to 'Le Grand K' to the distance light travels in a vacuum during 1/299,792,458 of a second.

But why does it matter whether or not 'Le Grand K' is the perfect kilogram? Because the standard needs to be standardised. Mental Floss says, the little changes can add up to be a big problem. Specifically:

The kilogram is also used as a building block in other measurements. The joule, for instance, is the amount of energy required to move a one-kilogram weight one meter. The candela, a measure of the brightness of light, is measured in joules per second.

These links mean that if the kilogram is flawed, so are the joule and candela, which could eventually cause problems in an array of industries, particularly in technology. As microchips process more information at higher speeds, even tiny deviations will lead to catastrophes. Le Grand K's unreliability "will start to be noticeable in the next decade or two in the electronics industry," warns NIST physicist Richard Steiner.

Read more about the flawed perfect kilogram at Mental Floss. [Mental Floss]


    1 J = 1 N.m

    1kg is not 1N

      ... and one Newton = "the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared."

      The point is, the kg will have an effect.

    Higgs Boson - the answer to everything these days...or the Carbon Tax

      ... what about the upcoming Higgs Boson Tax?

        Dont give them any ideas... oh too late

          I say a tax on all bos(u)ns, both Higgs and seafaring.

            Bwhaha. Best Higgs joke so far. I'll be sending this to all the dibbies at work

    It must be travelling at a negative fraction of the speed of light... or is it evaporating?

      Neither. The linked article states that the likely culprit is the copies of Le Grand K are gaining weight due to being handled more often or that the original is outgassing; air trapped in the weight during it's creation is slowly escaping.

      With the spees of light slowing maybe they will even each other out anyway ^^

    Wait so why is this mass, losing mass?

    Corrosion, decay or.....?

      Yeah I expected the explanation also.. From the Mental Floss link:

      At its most recent weigh-in in 1988, it was found to be 0.05 milligrams—about the weight of a grain of sand—lighter than its underling replicas. Experts aren’t sure where this weight went, but some theorize that the replicas have been handled more often, which could subtly add weight. Others postulate Le Grand K’s alloy is “outgassing,” which means air is gradually escaping the metal.

      Well, the universe is expanding and there's only enough gravity to go around.
      There is, therefore less gravity in any one area now than there used to be.

      Seems legit?!

    Just need someone to count the number of atoms in the Le Grand K and set it at that. Just as time is now the number of orbits of an electron.

      The catch there is that it needs to have a permanent isotopic ratio- you can say "x number of atoms of Carbon" but if it's not isotopically pure it'll change over time.

    Im sure there are already other objects that are a kilogram. If not make another one

      And with what will you measure it, Dear Henry?

        The same 'thing' they measured the other one with that is 0.05mg too light?

          And in 10/20/100/10,000 years from now we are faced with exactly the same problem. I believe that is the gist of the rhetoric from olearymo (?).

          So long as a unit of measurement is defined by a physical object it will be subject to the same degradation of accuracy over time. Which I can only presume was the impetus behind the decision to define 'the metre' by a theoretical constant (speed of light in a vacuum) as opposed to an inanimate carbon rod ... er "metal rod".

    I am wondering what validity would a stuff like that would have as the gravity fluctuates all the time and is different form one place to another.
    What s the worth of a weighting at paris.

    Why not Just Use apples..... Isaac did...

    Any solid object loses atoms all the time.... they just evaporate... (yes solids do have vapour pressure)

      Very interesting point. An example is ice evaporating into air without going through a vapour phase.

      The rate at which a solid will out-gas is likely to be affected by air pressure, suggested by the fact this kilo standard is stored within a triple vacuum. I'm assuming it is stored this way to ensure it cannot form an oxide and change weight due to any such subtle corrosion chemical change.

      Radioactive decay of any isotopes, especially impurities would be a factor too.

      Nevertheless, some overenthusiastic French Polishers might have given the sample a happy ending ! ; )

    I'm pretty sure this is why my body is now made up of more kilograms than it was 2 years ago....

    Someone is working on making the world's most perfect sphere of some pure silicate crystal to be 1-kg, and then a measurement of the sphere diameter will yield it's volume and hence number of atoms (a VERY perfect crystal), and the kg would be reduced to x number of Silicon atoms.

    They discovered a relative measurement solution to the Kilogram problem a year ago. OLD Irrelevant news OLD.

    Hasn't it been theorised that the speed of light isn't constant either? Certainly, the supposed rate of decay is so small that it will not be discernible during the existence of the human race, but that's just another prediction taking into account today's level of technological sophistication - I would have trouble trying to accurately predict the state of anything in 100 years.

    I guess the point is, surely it was once thought that a kilogram is a kilogram is a kilogram, and Le Grand K will stand testament to that immutable fact. Times change and now we're seeing the error of comparison dependency, so we want to measure the kilogram against something else - and in 2145 they can snicker at how foolish we were to believe that what we picked would be constant.

    Obviously, the only way to be sure is to create cyclic dependency, and measure a kilogram as the amount of weight that can be moved one meter using one joule.

    I didn't finish my physics degree, but I can see how this is a mega problem that must be solved. But then again I gave up on my degree when I also found out that the speed of light is slowing down as the universe ages, and the uniform attraction of gravity at point a is different at point b on the same planet. The differences are miniscule, but when you're talking about calculations at 12 decimal places it becomes signifigant. That's right, you are heavier or lighter depending on where you stand. And don't even get me started on planck's constant.

      how about this: If you live in a low-lying area, time goes faster than someone who lives at altitude ;)

      (gravitational time dilation)

        doh! - I mean slower :S

    Can't they just go to Safeway and get a 2 kg tub of ice cream; eat half (and only half) and the remainer will be exactly 1 kg...

      No, because that doesn't take into account the weight of the tub. Duh! It gets worse if you forget to take out the spoon you've used.

    I don't get this.

    The whole beauty of the metric system to me is it's inter-relatedness.

    I thought a kilo equalled a litre of water and a litre is 1000 cubic centimetres.

    So if they have decided on an unchanging measure for the centimetre as stated in the article, surely that translates into an unchanging measure for the kilo also? (as long as you decide on an exact temp and pressure (same thing?) for the water).

      Essentially what you are saying is that a certain number of H2O molecules should be the standard. i.e. the number that fit into a 10cm cube at some arbitary temperature. I believe this is how they intend to solve it, but using silicon atoms rather than water.

        Except not in a 10cm cube.

      The density of water will change at different temperatures. Meaning 1L of water will not always equal 1kg.

    Is it losing weight or losing mass? Two different problems....

      Two different concepts, but the same problem.

    Hmmmf... and we thought the Y2K bug was bad.... this surely must mean doom to us all!

    How can you know its losing weight if that is what defines the measurment?

    Did someone forget to write down the original weight? :)

    maybe the scales which they placed it on needs re-calibration?

    They never explained how the Kilo might be losing mass. As mentioned, maybe the scale just needs recalibration aka exactly why the kilo was used in the first place.

    Had somebody who specialises in exact measurements come and talk to our Physics class, apparently the weight is decaying slowly and at the moment they're trying to define the exact number of Carbon atoms that would make up 1Kg

    Weight = mass x gravity, so is the mass changing or the gravity?

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