Exactly One Kilogram Of Silicon 95
Ed Pegg Jr writes "You may know of the importance of 299792458
for length, and 9192631770 for time. However, the official standard for weight is still a block of platinum/iridium made a hundred years ago. A group of scientists from the Avogadro Project are hoping to change that, though, by producing a perfect sphere of ultrapure silicon."
A perfect sphere? (Score:5, Funny)
Pi is still irrational, isn't it?
Don't tell me the all my math teachers lied to me!
Re:A perfect sphere? (Score:5, Funny)
And worrying on the quark level might make you a little irrational too
Re:A perfect sphere? (Score:2, Funny)
Re:A perfect sphere? (Score:2, Funny)
My girlfriend already has a couple of perfectly round 2.2lbs of silicone; and don't ask for photographic proof.
Forgive this arguement if it sucks, but (Score:1)
Honest Question (Score:5, Insightful)
Re:Honest Question (Score:5, Informative)
What exactly is the benefit of having an object with a mass of exactly one kilogram
To calibrate scales.
Re:Honest Question (Score:3, Funny)
Re:Honest Question (Score:5, Informative)
Re:Honest Question (Score:2, Funny)
Re:Honest Question (Score:2, Funny)
Re:Honest Question (Score:5, Funny)
Re:Honest Question (Score:3, Funny)
You put one on the table, and the perphect sfere sits on the hole.
Re:Honest Question (Score:2)
Mmmmmm.... silicon....
Re:Honest Question (Score:2)
By making the surfaces of the sphere and the scales nearly perfectly smooth! :) That way, friction will be very high.
I once saw a video of a very smooth sphere rolling down a very smooth vertical surface - it rolled very very slowly (a barely perceptible movement).
Re:Honest Question (Score:2, Interesting)
how will they measure the mass of their new sphere? that's right...against the cube (actually, the cube's specs). when the new kilogram is accepted, will they lend it out to calibrate scales? nope. it will sit in a room as an oddity, just like the cube has for most of its life.
Re:Honest Question (Score:2)
The current definition of the kilogram is "the mass of that lump of metal near Paris". We the define other constants, such as Avogadros's number, in term of that kilogram
Re:Honest Question (Score:2)
Re:Honest Question (Score:3, Interesting)
Re:Honest Question (Score:2)
Do we know, mathematically, how much a kilogram is?
Yes. Exactly 1/12th mol of Carbon-12. However, that may take some time to count.
Mathematics != Real World (Score:5, Informative)
Pi does not exist in the real world. If you don't agree, show me an object in the real world that has exactly pi length, weight, or volume.
By contrast, the kilogram is an idea (an agreement really), that leads to a real world object (bar of platinum, sphere of silicon) that people can test their measuring devices against.
Ask yourself this: if you and your friend had two scales, how would you know which one is more accurate?
Answer: you would test them against a scale you agreed was more accurate.
But, in order to test for accuracy, you need a very "accurate" object. You need something that everyone agrees weighs a certain amount (say a kilogram?) And your "most accurate" scale had better exactly weigh that object as exactly one kilogram.
That's basically what calibration is: you take an object you declare to be 1 kg (or 1 g) and then you set your scale to indicate it as such. Obviously, there is more to it than that, but that's the very basics.
Science relies tremendously on these types of standards. One of the biggest (and unsung) "wins" of the 20th century was the tremendous increase in the objective standards of accuracy. Imagine trying to build a microprocessor if everything was designed in terms of hand lengths or feet lengths of the various contractors. Without increasingly tight, objective standards of measurement, modern science and technology would not exist.
Ironically enough, I'm a mathematician. I would encourage you to talk to a professional scientist or engineer and ask them about it.
Approximation of Pi in the real world (Score:1)
Re:Mathematics != Real World (Score:1)
Re:Honest Question (Score:2)
So, we need new, more precise methods of defining things like how much mass one kilogram has.
Or something like that
Re:Honest Question (Score:2)
They want to do it without changing the actual value of the kilogram by more
than 1 part in 10^8 (the accuracy to which the current standard is consistent).
To do that, they need to determine the mass of an object and the number of atoms in it to a combined accuracy of better than 1 in 10^8. In principle, once they have done this, they can throw away the object.
One
Next they need to work on NULL pointer checks (Score:4, Funny)
I'm tired of reassuring the coding standards people that, yes, such-and-such a pointer has been tested against the platinum/iridium void* kept in a vault in Paris.
Old news (Score:5, Funny)
Pam Anderson has already cornered this market.
Ohhhh, silicon...
Re:Old news (Score:2, Funny)
There's only one of these, and it only weighs one kilo.
Re:Old news (Score:3, Funny)
Twice!
Stick it to the French (Score:5, Funny)
Re:Stick it to the French (Score:1)
How many perfectly pure balls of silicon are in a gallon of wine anyhow?
why kilogram? (Score:4, Interesting)
why is the unit for mass the kilogram when it should more logically be the gram?
using the gram might be easier to accurately measure too.
Re:why kilogram? (Score:4, Informative)
We've got cgs (centimeter-gram-second) and MKS (meter-kilogram-second) systems, and at least one more.
If you're not satisfied, make your own. And watch the rush to adopt it!
I'm partial to MKS myself; less silly multiplication by powers of ten to correct units.
Re:why kilogram? (Score:5, Informative)
centimeter - gram - second
meter - kilogram - second
It's just a matter of names. Logically, either system should be all "basic" units, with no prefixes. If a meter happened to be defined as 1/100th the current length, then you'd have the "meter gram second" system for the first case, and it would make more sense.
Of course, you still have the problem that a kilo of water is a cubic decimeter, not a cubic meter. So in the MKS system, you'd have to have a "gram" weighing rather inconveniently 1000 times as much, and a meter 1/10th the size, to make this "meter gram second" system more consistent.
The real answer, of course, lies in that word "convenient". The metric system, despite the claims of some proponents, is not really particularly inherently logical. Sure, it uses powers of ten. But the units themselves were chosen completely arbitrarily. And they were chosen simply to be relatively close to units already in use at the time - yards, bushels, pounds, quarts, and so on, because those were convenient sizes people were used to, not because there was some overriding scientific reason for choosing those sizes. (1/10^7 of the distance from Paris to the North Pole, indeed. Talk about chauvinisitic... as if there were a fundamental scientific principle rooted in the location of Paris!)
A truly "scientific" system would have units sized on fundamental constants - speed of light, Planck's constant, permitivity/permissivity of free space, all those sorts of numbers. You'd know you had such a system because they would be nice round numbers rather than arbitary long strings of digits as they are in the current metric (or English) system.
And when it comes to prefixes, you could always argue that the English system is far more logical in the age of computers. The metric system goes by powers of ten, which happens to be convenient for manual calculation. But the English system goes by powers of two; e.g, 16 cups = 8 pints = 4 quarts = 2 half gallon = 1 gallon. Much nicer for computers; no roundoff error there in the floating point processor, and you can change units by a simple shift operation rather than the hugely more time-consuming multiplication by ten. Same logic, different base.
meter nit (Score:5, Informative)
1/10^7 of the distance from Paris to the North Pole,
Actually, the meter was defined as roughly 1e-7 of the distance from the equator to the North Pole along Paris's meridian, making the earth roughly 4e7 m (40,000 km) around.
Re:why kilogram? (Score:5, Funny)
Still, just try getting a .75 centipace wrench. You can't even order them, and without that, just how the hell are you supposed to repair the flux capacitor?
Re:why kilogram? (Score:4, Interesting)
Yes, 3 feet to the yard (for surveyors, 66 feet to the chain), 1760 yards to the mile...
Please, tell me how to use a shift operation to divide by 1760. :P The other nice thing about metric is the consistent prefixes. There is one MKS symbol for length (m), not many (in, ft, yd, mi...) and it can be associated with a set of prefixes (micro, milli, kilo, mega, etc.) that have consistent meaning across all metric units. For us humans, it is easy to find a unit that lets you express values in "comfortable" form--living cells are on the order of 10 micrometers across, not 0.00001 meters; it's 100 kilometers to Grandma's house, not 100000 meters. And since it's in easy powers of ten, I can tell you immediately that you can line up 10^10 cells along the road to Grandma's, if you want to know.
Re:why kilogram? (Score:2)
So does that mean that I should say that I have 1 gram of wheat or 1 millikilogram when I use the MKS system?
Re:why kilogram? (Score:3, Informative)
I know you're just joking, but SI (the metric system) does deal explicitly with this. You can use one prefix, at most.
Engineers are in the habit of occasionally abusing this convention--instead of using u (mu, for micro-, 10^-6) as a prefix for some units (uH, microhenries of inductance) they will use mm (millimilli, presumably, as in mmH).
As far as I know, nobody ever combines prefixes associ
Re:why kilogram? (Score:2, Funny)
= 128 ounces = 256 tablespoons = 768 teaspoons =
Converting inch-pound mass and weight to mks (Score:1)
how're you going to work with slugs in cgs or mks?
To go from inch-pound to mks, convert slugs to kg (1 slug = 14.594 kg), and pounds to newtons (1 lb = 4.448 N).
Re:why kilogram? (Score:4, Interesting)
Case in point - I was working with pressure instrumentation this week, and have a new appreciation of what absolutely *insane* units have to be used by the poor folks that prefer metric.
I'm talking, of course about that riduculous unit the Pascal, that defames the name of one of history's great scientists and thinkers.
The idiot who decided that a pressure as ridiculously low as one Newton per square meter was a useful unit of pressure should have been stood up against the wall and summarily shot. That such a thing exists as an ISO standard seems to fit the inherent silliness of every ISO-developed standard I've ever encountered.
I'm only half joking. This is such a ridiculously low pressure that any sort of real-world engineering use requires kilo-, or more likely megaPascals in order to express it. To put this silliness in perspective, realize that the very low pressure of 1 Atmosphere is equivalent to 101,325 Pascals. No wonder the civilized world calls it 14.7 psi instead...
Re:why kilogram? (Score:2, Funny)
because they would then need a standard unit for the value of "one thousand". Duhhhh!
Re:why kilogram? (Score:2, Funny)
BILLY! (Score:5, Funny)
Get in here this INSTANT, and bring it with you! When your father [nist.gov] gets home you are going to be grounded, young man! Two weeks to the PICOSECOND by the atomic clock in the kitchen. Now go stand in the corner, and NO LEANING! You'll probably throw the wall out of plumb, or expand the angle to 90.7632+1E degrees or something, you troublemaker!
To Mr. Pegg (Score:5, Informative)
ITYM mass. SI has no unit for weight. There's the newton for force, but it is not defined in terms of gravity. It is also not a SI base unit.
Re:To Mr. Pegg (Score:4, Funny)
2.1.1.2 Unit of Mass (kilogram)
The international prototype of the kilogram, made of platinum-iridium, is kept at the BIPM under conditions specified by the 1st CGPM in 1889 (CR, 34-38) when it sanctioned the prototype and declared:
'This prototype shall henceforth be considered to be the unit of mass.'
The 3rd CGPM (1901: CR, 70), in a declaration intended to end the ambiguity in popular usage concerning the word 'weight' confirmed that:
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
Re:To Mr. Pegg (Score:1)
What do you think a newton is? The force exerted by one gram begin accelerated at one G (or its weight at one G).
Re:To Mr. Pegg (Score:3, Interesting)
A newton is defined as 1 kg-m/s^2. As the AC already stated, you're off by roughly a factor of 100, and even that isn't exact.
New Austin Powers movie plot. (Score:5, Funny)
What an idea.
Re:New Austin Powers movie plot. (Score:3, Funny)
Did anyone else think of... (Score:5, Funny)
Warning: Pregnant women, the elderly and children under 10 should avoid prolonged exposure to Happy Fun Silicon Ball.
Discontinue use of Happy Fun Silicon Ball if any of the following occurs:
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Do not taunt Happy Fun Silicon Ball.
Happy Fun Silicon Ball
Accept no substitutes!
Diamond (Score:3, Insightful)
Re:Diamond (Score:1)
Re:Diamond (Score:1)
Re:Diamond (Score:5, Informative)
Diamonds are *not* forever.
Why does it have to be a SPHERE? (Score:4, Interesting)
Is there some inherent problem with other geometries?
Like, say, the cylinder ( as the original kilogram were )
Isn't machining a sphere, perfectly, more .. error-prone?
Re:Why does it have to be a SPHERE? (Score:4, Informative)
Please RTFA (Score:1)
Re:Please RTFA (Score:2)
Sorry, I'd been thinking-of a rounded-edge-cylindar, not a sharp-edged-one... ( or a rounded-tablet, or something )...
..but simply putting the thing down onto a cradle will change its mass, whereas with a flat-bottom'd object, it could be placed on a fluorinated diamond surface ( on a gimbal-table, like they used to have in ships, 'cause it'd be slippery ), and gain/lose rather close to nothing, and thereby remove that source-of-error...
Re:Please RTFA (Score:2)
If they do this,
-sigh- it isn't silicon, it's nitrogen-doped Si (Score:2, Funny)
in other words, I DID read the thing, and they're using nitrogen-doped-silicon to suppress, what was it ? spiral .. swirl defects, so the sphere isn't pure crystalline silicon, to begin with, AND...
they're measuring it by diameter, which isn't, I'd a' thought, the perfect way to discover how many atoms are in the object, and
they're using IT as a reference, so therefore they are using the object as a reference, so changes in mass ( due to some infinitesimally teensy amount being acquired-from or lost-to
Please Correct me (Score:3, Interesting)
If I'm correct what is the point? They should worry about what makes a liter and what is pure water.
Re:Please Correct me (Score:1)
Re:Please Correct me (Score:2, Funny)
You are correct in thinking that you will be corrected :)
Water is roughly 1000 kg/m^3; it's also roughly 1 g/cm^3 which is how I originally learned the ratio (there are 10^6 cm^3 in a m^3).
I went to public US junior and senior high schools, all the science I lear
Re:Please Correct me (Score:1)
Okay, you asked for it (Score:5, Informative)
Water expands and contracts as the temperature and pressure around it change, even in the range where it is still liquid.
It turns out that liquid water at 1 atmosphere pressure is most dense at about 4 degrees Centigrade, where its density is 0.9999750 g/cm^3. at closer to room temperature- at 22 degrees C- its density is only .9977735 g/cm^3. It never actually gets up to 1 g/cm^3 the unit system was originally designed to use, I think because of the limits of accuracy of measurements when the current definitions of individual units were set. In defining a unit, all those significant figures are relevant, so for these purposes the above are unacceptably big differences.
Measuring mass by what the volume of water is would be more complicated and less accurate than the current system. Besides, a liter is trickier to define than a kilogram, so it'd likely be the other way around if defined in terms of each other.
Re:Okay, you asked for it (Score:4, Interesting)
This extremely unusual quirk of water (along with its inverse density as a solid) is one of the chief reasons that stable oceans are pretty much impossible with other substances, despite waht science fiction authors like to imagine: Because water is densest at 4 C, the entire volume of a body of water has to first reach that temperature (since it sinks to the bottom at that temp) before freezing at the top. Any other scenario results in bad things happening, like, say, all bodies of water freezing solid, making the continuation of life through winter rather difficult for aqautic species... One more reason to question whether naturalistic notions of origins really hold up under close scrutiny. (Don't even get me started on eclipses...)
Re:Okay, you asked for it (Score:1)
Ice-9 anybody?
Re:Okay, you asked for it (Score:2)
and we have defined a meter as a fraction of the distance that light travels in 1 second, so I fail to see the problem in defining a litre.
that won't help much (Score:5, Interesting)
Secondly, it doesn't matter either what exactly is 1 kilogram. what matters is some reference atomic mass and then pick up Avogadro number (based on existing 1 kilo mass) and then get rid of the existing standard. this would allow independent reproduction (e.g. 1 kg is equivalent of 6.02...... x 10^23 atoms of Oxygen 16 in certain energy state. this scheme too has problem. there is no practical way of verifying that you have met the standard definition. so, two scientists can argue that each is possesing exact 1 kg and this cannot be arbitrated.
Re:that won't help much (Score:3, Informative)
And then:
what matters is some reference atomic mass and then pick up Avogadro number (based on existing 1 kilo mass) and then get rid of the existing standard.
Doesn't the use of an Avagadro number of atoms, of specified number of protons and neutrons, exactly solve the weight description problem? You've got a point about ensuring that the ensem
Re:that won't help much (Score:1)
Re:that won't help much (Score:1)
Ian.
Re:that won't help much (Score:3, Informative)
That difficulty is the only reason the kg hasn't been redefined already--a standard definition isn't very useful if you can't actually implement it.
Measurement History (Score:1)
Anyone know of any good books about the history of measurement?
Like what came when and how things like horsepower or slugs and pounds came into use and how they originated?
I know about how stuff works type webpages, but I'm looking for a book with indepth info about English-Metric and whatever systems there used to be.
Thanks!
Correction (Score:2)
How does this relate? (Score:1)
Is this more than a handful or less?
Horta (Score:2)