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United States Science

US Objects To the Kilogram 538

Posted by Soulskill
from the weighty-subjects dept.
Velcroman1 writes "For 130 years, the kilogram has weighed precisely one kilogram. Hasn't it? The US government isn't so sure. The precise weight of the kilogram is based on a platinum-iridium cylinder manufactured 130 years ago; it's kept in a vault in France at the International Bureau of Weights and Measures. Forty of the units were manufactured at the time, to standardize the measure of weight. But due to material degradation and the effects of quantum physics, the weight of those blocks has changed over time. That's right, the kilogram no longer weighs 1 kilogram, according to the National Institute of Standards and Technology. And it's time to move to a different standard anyway. A proposed revision would remove the final connection to that physical bit of matter, said Ambler Thompson, a NIST scientist involved in the international effort. 'We get rid of the last artifact.'"
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US Objects To the Kilogram

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  • Weight a minute... (Score:1, Insightful)

    by Anonymous Coward on Friday October 29, 2010 @02:46PM (#34066730)

    The US cares that much why? Its only a trade matter, as we still use primitave imperial measurements. Maybe if we had switched to metric like they had told us we were going to every year in grade school this would be a big deal, but right now, who cares?

  • by Slutticus (1237534) on Friday October 29, 2010 @02:52PM (#34066832)
    ..is about a decimal place in which the instuments available to most of us can't even touch (precicion-wise...) But by all means, carry on.
  • Re:Who cares? (Score:5, Insightful)

    by cool_arrow (881921) on Friday October 29, 2010 @03:03PM (#34067010)
    Without cocaine and weed so many american kids would know absolutely nothing about the metric system. Think of the children!
  • Re:BASE16 (Score:3, Insightful)

    by Conspiracy_Of_Doves (236787) on Friday October 29, 2010 @03:04PM (#34067026)

    All bases are base 10

  • by bdcrazy (817679) <bdc_tggr-forums@yahoo.com> on Friday October 29, 2010 @03:08PM (#34067106) Homepage

    I just love ideal physics land. Unfortunately the real world doesn't work that way.

  • Re:Who cares? (Score:1, Insightful)

    by Anonymous Coward on Friday October 29, 2010 @03:15PM (#34067274)

    Seeing as you still posted, I'm voting for not saving you effort.

  • by goodmanj (234846) on Friday October 29, 2010 @03:22PM (#34067402)

    Ugh. I teach college intro physics, and even *I* think that's a sociopathically pedantic distinction.

    In my class, I'm happy to use "an object weighs 5 kilograms" to describe the mass of something. I'm just careful to call the gravitational force on the object the "gravitational force", and never the "weight".

    It's all clear and consistent unless you try to use the Imperial system, in which the pound is a unit of force. So I don't.

  • by goodmanj (234846) on Friday October 29, 2010 @03:34PM (#34067576)

    This is Fox News. From their perspective, *all* concerns are political concerns.

    Global warming, economic policy, genetic engineering, epidemiology: all of these are relevant to Fox News (and MSNBC etc) only for their impact on the great battle between conservatism and liberalism.

  • by goodmanj (234846) on Friday October 29, 2010 @03:36PM (#34067610)

    Second, I don't care what the experts say, a kilogram is equal to the mass of one litre of water, which is equal to 1000 cubic centimetres of water, or a 10cm x 10cm x 10cm box full of water.

    Does it have to be pure water, or can it have some impurities in it? What temperature is the water? What pressure? When you're trying to do especially delicate measurements, these details matter!

    The "weight of a liter of water" will continue to be the useful informal definition, but we need something more precise for technical use.

  • Re:Roundest (Score:3, Insightful)

    by JSBiff (87824) on Friday October 29, 2010 @03:37PM (#34067626) Journal

    I don't think so. One of the goals of the metric system over the past century has been to find ways to define the units in terms of fundamental physical constants, as opposed to something completely arbitrary like creating a block of some material and saying "this block is a kilogram". The definitions, by nature are still going to be somewhat arbitrary, but at least once you make the arbitrary definition based on a physical constant, it's easy to reproduce. We could explain to an alien 1/2 way across the galaxy what a second or a kilogram, or a meter is, by telling them a 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 caesium 133 atom."

    As long as they are technologically advanced enough to understand that, and to precisely figure out how long that takes, they'll know what a second is. If they aren't advanced enough to deal with that, we can tell them "It's about the amount of time it takes to say 'one-one-thousand'."

    More importantly, throughout history, once we have a reasonable definition based upon a fundamental physical constant, we don't have to worry about the units changing value.

    Obviously, to most people, having such a level of precision for what a unit is, is not necessary, but for scientists and engineers, in some cases it is very necessary.

  • by ultranova (717540) on Friday October 29, 2010 @03:42PM (#34067694)

    I just love ideal physics land. Unfortunately the real world doesn't work that way.

    Actually, it does. You do know that's what physics is all about, right?

  • by asher09 (1684758) on Friday October 29, 2010 @04:27PM (#34068294) Homepage
    H2O is known to weigh 1000 g/L at 4oC with the current metric system. So if we define 1 kg = 1L of water at 4oC at 1 atm, or 55.50843 mols of water, anybody anywhere in the world can have the precise and accurate standardization for kg.
  • by Goaway (82658) on Friday October 29, 2010 @04:30PM (#34068326) Homepage

    Well how frickin' accurate do you want to be?

    Very, very frickin' accurate. That is the whole point.

  • by Goaway (82658) on Friday October 29, 2010 @04:38PM (#34068396) Homepage

    The point is that the definition needs to be practical. We need to have a way to actually measure a kilogram using the definition, so we can calibrate our scales. If we can not use the definition to calibrate a scale to some very high accuracy, it is useless.

  • by DerekLyons (302214) <fairwater&gmail,com> on Friday October 29, 2010 @04:39PM (#34068420) Homepage

    If counting and weighing photons were so easy... you'd have a point. But it isn't. Pretty much every proposal for replacing the kilogram standard so far has either ended up in a circular definition, or required us to do something we don't actually know how to do.

  • by Tanuki64 (989726) on Friday October 29, 2010 @06:38PM (#34069548)
    If Americans want to redefine the kilogram it most likely means that in the next step they try to get royalties whenever someone weighs something.
  • Re:BASE16 (Score:1, Insightful)

    by Anonymous Coward on Friday October 29, 2010 @09:45PM (#34070546)
    No I didn't mis-convert it to 3967 that was just a number I picked out of the air. You "arbitrarily" picked an easy number to do in base10 though with 4000.

    In base16, 1000 is 4096 in decimal.
    Look, 1000^2 is 1,000,000 or 16,777,216 (24bit) in decimal

    Just adding 0s to 1000^2 works in base16 just as well as it does in decimal. ;-)

    100 =256
    100*100 still equals 10,000 in base16. ;-)

    The properties of multiplication don't magically change just because the place values can hold more or less.

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