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Experts Suggest Replacing Definition of Kilogram
fenimor writes "The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon. International team of scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms. They propose to adopt either one of two definitions for the kilogram by selecting a specific value for either the Planck constant or the Avogadro number."
They set it to 1000 grams.
I'm going to finally lose some weight?
The Answer
The next thing you know they will be trying to get the US to switch from imperial units to the metric system....
http://jayceecorder.blogspot.com
I'm going back to pounds and stones.
Educated guess: It'd be the most expensive thing the size of a "plum" made of platinum-iridium ever sold on eBay.
more importantly, what would they list it's shipping weight as?
FGD 135
Pi is exactly equal to 3!
The SI unit of mass is the kilogram, not the gram.
Picture of the International prototype kilogram:
y pe.jpg
http://www1.bipm.org/utils/common/img/mass/protot
That would work fine, and I believe was the original definition. Unfortunately, pressure has a mass component, so your definition is circular.
Lisa: Principal Skinner, how's your transportation project coming?
Skinner: Not only are the trains now running on time, they're running on metric time! Remember this time people, 80 past 2 on April 47th. It's the dawn of a new enlightenment!
Just in case people care, here are the 7 base units:
... or something.
Metre for Length
Kilogram (what this article is about) for Mass
Second for time
Ampere for current
Kelvin for temperature
Mole for amount
Candela for "Luminous intensity"
All the others are built up and defined from these, so these must be well defined. Change what exactly a Kg is changed more than just mass - it changes everything dependant upon it. Hence, these things must be got right.
The definition of second changes every now and then though, and I think the metre has changed a few times, too. I wrote a bit about the second here, in my AS-Level Physics coursework, if anyone want s a simplifed read.
(Wiki)
I don't see how this topics is maths, by the way.
- Jax
The second and the meter have long since been based off of more fundemental measures. The second is defined as how long it takes for 9,192,631,770 cycles of microwave light to be emitted by the hyperfne transition of cesium-133 atoms. The meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
A deep unwavering belief is a sure sign you're missing something...
You'd lose mass instead.
"[Regarding the 'cloud,'] ownership was what made America different than Russia." -- Woz
The point is to have something that you can define just by counting some phenomenon or natural objects. For example a second is defined as:
"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."
and a metre is defines as:
The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
Unfortunately, there hasn't been a good way to count the number of atoms with any kind of precision, so that has precluded a good definition of the kilogram so far. Maybe now the physicists can actually count atoms accurately enough.
One could define it as the mass of some number of H2O molecules, but maybe its easier a measure a quantity of light or to count some larger atoms.
It is well known there are 7 base units.
"Candela essentially measures the same things as watts."
But watts are not a base unit. A watt is the same "Joules per second", and Joules is also not a base unit, but is defined as a Newton Metre. But a Newton isn't a base unit, it is defined as a Kilogram Metre per second per second. So:
Newton = kg.m.s^-2
Joule = Nm = kg.m.s^-2.m = kg.m^2.s^-2
So a watt is in-fact a kg.m^2.s^-3 , or "Kilogram metre squared per second per second per second" - hence changed the kilogram will change the watt, despite them seeming unrelated!
A mole isn't the same as mass at all. It is more to do with things on an atomic level. It's really used in chemistry - I've personally never used it outside of a chemistry exam (or coursework). It is sort of just a number, but it actually isn't.
Kelvin is a fundamental base unit too. Momentum is defined as "Newton Seconds", and so (remembering the definition of a Newton) kg.m.s^-1. Kelvin's measures temperature, which is a measure of kinetic energy, so I can see where you are coming from. You're just wrong.
Ampere is too. Helpfully, from it you can define other helpful things like volts. A volt, for your interest, is defined as kg m^2 s^-3 A^-1 , or "Kilogram metre squared per second per second per second per amp". And so yet another thing this change would affect.
It's all very interesting.
- Jax
They are cleaning the definition, not the value.
;-)
A new kilogram with equal an old kilogram. This will only make a difference to the history books and those who actually want to make thier own 'kilogram'.
I can imagine how many 'net savvy drug runners are looking at this and thinking, 'shit, I have snorted too much coke, does this affect my business? whats a planck? oh man, Avocado constant? [sic]
I say since the kilogram was an arbitrary measurement (in any definition) then why try and make it more formalised? I realised that celcius fit nicely with pure water at sea level freezing and boiling, and other measures have thier own basis (has the definitions have changed). Take my friend the meter. I always use the old skool definitions for rules of thumb.
Year Definition
1793 1 / 10 000 000 of the distance from the pole to the equator.
1795 Provisional meter bar constructed in brass.
1799 Definitive prototype meter bars constructed in platinum.
1889 International prototype meter bar in platinum-iridium, cross-section X.
1906 1 000 000 / 0.643 846 96 wavelengths in air of the red line of the cadmium spectrum.
1960 1 650 763.73 wavelengths in vacuum of the radiation corresponding to the transition between levels 2p10 and 5d5 of the krypton-86 atom.
1983 Length traveled by light in vacuum during 1 / 299 792 458 of a second.
So you see, a meter was the same in all these cases, but they just wanted to act clever.
The thing is, after world war 3, which measure will be easiest to revert to for a meter? trying to find scientist who can measure "Length traveled by light in vacuum during 1 / 299 792 458 of a second." or just comparing a brass stick with a length of wood while trying to build something using pre-existing specs (that you are relying on to build a post WW3 bridge).
#hostfile 0.0.0.0 primidi.com 0.0.0.0 www.primidi.com 0.0.0.0 radio.weblogs.com
2.2 pounds, of course. :)
The weight formerly known as kilogram.
No, there is one definitive 'Kilogram' which is kept in Paris, and then copies are made and shipped worldwide to save countires having to go to Paris to check their official weights. The copies are then compared to the one true kilogram every 10 or so years (dependant upon whether it's being used for a quest to save mankind at that point).
How many people can read hex if only you and dead people can read hex?
As far as what the NIST says, that is baloney
I had been wondering if NIST was just pulling these so-called standards from their ass. I am glad you confirmed it. From now on, a kilo is the amount of coke a mexican hooker can snort in one week. Or course, that is under STP.
Given that the kg prototype has lost 50 micrograms over the last 100 years I'm guessing 0.999995kg?
As technology to measure substances to great precision increases, its about time the kilogram got a redefinition as well, one not based on a single object.
Where you actually need to use them directly, sure.
To give a real world example of how the standards work in practice... I used to write software for a company in the metrology (high precision measurement) business. They made machines that are used, for example, in quality control at the end of production lines. The gauges on the most popular machines gave accurate readings with resolutions of say 1-10m.
Those machines were calibrated from reference artifacts. These were themselves checked for accuracy on still higher precision equipment. (How they actually manufacture something so close to physical perfection is an interesting area in itself...)
Ultimately, there were white room areas with very careful decontamination procedures in place that were used almost exclusively for calibrating the company's most precise equipment and checking their reference artifacts.
From there, you were one step removed from the national standards laboratories. At that level the formal scientific definitions are just fine.
In other words, you work from major standards labs that can use the precise definitions effectively, and propagate the information (with some less, but little enough to be acceptable for the application in question) to more widely distributed testing facilities. A more trendy application of the same basic idea is the use of Internet-based real time clock services.
If you disagree, post your argument. (-1, Overrated) isn't your personal censorship tool for views you don't like.
How many Avogadroes are in guaca-mole?
I guess 6.02x10^23...
What you're talking about are "fundamental" units versus SI base units.
In a fundamental system of units, there are three base units: charge, mass, and angular momentum. (Gee, those sound suspiciously like the three properties that a black hole can possess - I wonder why). Everything else can be derived from those units (for the most part - we'll ignore stuff like baryon number, lepton number, etc. because those theories aren't complete yet. For instance, we now know that only global lepton number is conserved, not mu, e, and tau lepton number separately. I won't even touch color, as color is completely hidden anyway).
In fact, the existence of those units can be derived from the fact that space is invariant under the Poincare group, and has gauge symmetry.
However, those base units come because you've defined other constants to 1.
The problem is that several of those constants are imprecise and difficult to measure. It is easier to define a kilogram, for instance, then it is to somehow base it on the gravitational attraction of two objects, because G is horribly imprecise.
Similarly, it is easier to treat Kelvin as fundamental rather than derived from other units *if* Boltzmann's constant has poor precision.
So while it's *possible* to use fundamental-based units, it's often *impractical* and less precise. The base units in SI are those that can generate all other units with no loss in precision.
To give a very practical example, the mass of a proton is typically given in atomic mass units (amu) as ~1.007 amu. You might think that it should be given in grams, as "amu" isn't a fundamental unit of mass. But the conversion from "amu" to "grams" is less precise than the mass of the proton in atomic mass units. So in this case, "amu" would be appropriate as a base unit, as well as mass, even though the two can be directly converted.
The benefit is that you can compare the mass of a proton and the mass of a neutron in "amu", for instance, to better precision than you could in grams. It's similar (or was similar when SI was developed) with the other units.