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 Tags kilogram

15th November 2018, 10:32 PM   #1
rjh01
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The kilogram is about to be redefined

Reality is about to change. The kilogram which until now, has been defined as the mass of a certain artefact (or big K) held in a vault in Paris. They will define the kilogram by defining as planks constant as exactly 6.62607015 X 10^-34 Js. This then determines how big a kilogram is.

This will mean that the values for the kelvin, mole and ampere will all now be fixed.

Avogadro's constant will be 6.02214076 X 10^23
The charge on an electron will be 1.602176634X10^-19C
Boltzmann constant = 1.380649X10^-23J/K

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Or https://www.cnet.com/news/scientists...logram-weighs/

This thread is a duplicate of this one http://www.internationalskeptics.com...ad.php?t=90329. Started in 2007. So the discussion has been going on for some time. Come to think of it my science teacher mentioned it in the 1970s.
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 16th November 2018, 06:47 AM #2 casebro Penultimate Amazing     Join Date: Jun 2005 Posts: 17,817 And this will have a practical effect just how, even if my most accurate scale only weighs to 1/ 70,000 of a pound? (1/10 grain) How will it effect shipping cost per metric tonne ? How much will the defined weight of even the Earth change? __________________ It's hard to tell an intuician from a magician if you think that they are both pulling things out if their asses.
 16th November 2018, 06:55 AM #3 The Great Zaganza Maledictorian     Join Date: Aug 2016 Posts: 11,621 more importantly, how will it affect my bathroom scales? __________________ ETTD Everything Trump Touches Dies Last edited by The Great Zaganza; 16th November 2018 at 08:07 AM.
 16th November 2018, 07:32 AM #4 Sherman Bay Master Poster   Join Date: May 2002 Location: Wisconsin, USA Posts: 2,271 I'm so glad this has come to pass and now all uncertainty can be swept aside. Just yesterday, I was wondering if my kilogram was a little off.
 16th November 2018, 07:38 AM #5 Craig B Penultimate Amazing   Join Date: May 2011 Posts: 22,841 Originally Posted by rjh01 ... defining as planks constant ... So the inch is now defined to be "as thick as two short planks".
16th November 2018, 08:25 AM   #6
casebro
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Originally Posted by rjh01
Reality is about to change. The kilogram which until now, has been defined as the mass of a certain artefact (or big K) held in a vault in Paris. They will define the kilogram by defining as planks constant as exactly 6.62607015 X 10^-34 Js. This then determines how big a kilogram is.

This will mean that the values for the kelvin, mole and ampere will all now be fixed.

Avogadro's constant will be 6.02214076 X 10^23
The charge on an electron will be 1.602176634X10^-19C
Boltzmann constant = 1.380649X10^-23J/K

 YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website. I AGREE

Or https://www.cnet.com/news/scientists...logram-weighs/

Old number 6.022140857 × 1023
New number 6.02214076 X 10^23

This thread is a duplicate of this one http://www.internationalskeptics.com...ad.php?t=90329. Started in 2007. So the discussion has been going on for some time. Come to think of it my science teacher mentioned it in the 1970s.
Old number 6.02214085 × 10^23
New number 6.02214076 X 10^23

It looks to me like they are making a mole smaller. We are are being cheated out or OUR molecules! It must be Trump, in bed with industry, to cheat the little people of the world!

(The intarwebs need a new rule, like Godwinning, except with "Trump" instead of "Nazi". There, I did them both. )
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 16th November 2018, 08:35 AM #7 casebro Penultimate Amazing     Join Date: Jun 2005 Posts: 17,817 Originally Posted by rjh01 Reality is about to change. The kilogram which until now, has been defined as the mass of a certain artefact (or big K) held in a vault in Paris. They will define the kilogram by defining as planks constant as exactly 6.62607015 X 10^-34 Js. This then determines how big a kilogram is. ..,. So now that I know that, can I make my own artefact(sic) standard? It's going to take a mighty fine microscope to count all them Joules individually... I don't think they are going to be selling the IPK for scrap just yet. __________________ It's hard to tell an intuician from a magician if you think that they are both pulling things out if their asses.
 16th November 2018, 11:48 AM #8 casebro Penultimate Amazing     Join Date: Jun 2005 Posts: 17,817 Originally Posted by casebro So now that I know that, can I make my own artefact(sic) standard? It's going to take a mighty fine microscope to count all them Joules individually... I don't think they are going to be selling the IPK for scrap just yet. If I have a scale that is accurate to 11 digits, a file that I can use to grind off a few molecules (how many?), and a Joule-o-meter that measures to 12 digits, my answer would be in the 10^23 range. I'm off to the US Government Surplus site, they have EVERYTHING. __________________ It's hard to tell an intuician from a magician if you think that they are both pulling things out if their asses.
 16th November 2018, 11:55 AM #9 Elagabalus Philosopher   Join Date: Dec 2013 Posts: 5,810 Originally Posted by casebro Old number 6.02214085 × 10^23 New number 6.02214076 X 10^23 It looks to me like they are making a mole smaller. We are are being cheated out or OUR molecules! It must be Trump, in bed with industry, to cheat the little people of the world! (The intarwebs need a new rule, like Godwinning, except with "Trump" instead of "Nazi". There, I did them both. ) ******* Euros! They're making a mountain out of a mole hill!!
 16th November 2018, 01:18 PM #10 rjh01 Gentleman of leisure Tagger     Join Date: May 2005 Location: Flying around in the sky Posts: 25,714 Originally Posted by The Great Zaganza more importantly, how will it affect my bathroom scales? Good news. It will not. But if you want to do a science experiment that the result relies on how big a kilogram is, for the first time you can give consistent results. Until now doing the same experiment can give slightly different results in different countries because they define the kilogram slightly differently. This will have implications, though exactly what I am not sure. __________________ This signature is for rent.
 17th November 2018, 09:25 AM #11 Trebuchet Penultimate Amazing     Join Date: Nov 2003 Location: Port Townsend, Washington Posts: 26,994 __________________ Cum catapultae proscribeantur tum soli proscripti catapultas habeant.
 17th November 2018, 01:19 PM #12 rjh01 Gentleman of leisure Tagger     Join Date: May 2005 Location: Flying around in the sky Posts: 25,714 Originally Posted by Trebuchet Even better news! The definition of a pound will not change. It will remain as exactly 0.45359237 kilograms. __________________ This signature is for rent.
 17th November 2018, 01:37 PM #13 Elagabalus Philosopher   Join Date: Dec 2013 Posts: 5,810 Originally Posted by rjh01 Even better news! The definition of a pound will not change. It will remain as exactly 0.45359237 kilograms. Except in Germany where a pfund (Arc.) is 500 grams.
 17th November 2018, 09:25 PM #14 Trebuchet Penultimate Amazing     Join Date: Nov 2003 Location: Port Townsend, Washington Posts: 26,994 Or in Ye Olde Englande, its 240d. __________________ Cum catapultae proscribeantur tum soli proscripti catapultas habeant.
 17th November 2018, 10:45 PM #15 Brainster Penultimate Amazing     Join Date: May 2006 Posts: 17,573 I always thought that designing the kilogram as equal to the weight of a liter of water was a particularly brilliant way to ensure a standard value. __________________ My new blog: Recent Reads. 1960s Comic Book Nostalgia Visit the Screw Loose Change blog.
 17th November 2018, 11:35 PM #16 rjh01 Gentleman of leisure Tagger     Join Date: May 2005 Location: Flying around in the sky Posts: 25,714 Originally Posted by Brainster I always thought that designing the kilogram as equal to the weight of a liter of water was a particularly brilliant way to ensure a standard value. It is a good standard. Though trying to get a litre of pure water using certain concentrations of isotopes of hydrogen and oxygen will be very hard. Remember if the measurement is out by one part in 10^7 it is wrong. That is why I suggest it went out in the 19th century. __________________ This signature is for rent.
 18th November 2018, 10:23 AM #17 alfaniner Penultimate Amazing     Join Date: Aug 2001 Posts: 22,279 I thought the deterioration of the standard sample would amount to a few molecules and be virtually undetectable. One report I say said that is has lost enough to equal the weight of an eyelash. That seems particularly significant to me. __________________ Science is self-correcting. Woo is self-contradicting.
 18th November 2018, 04:05 PM #18 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by Brainster I always thought that designing the kilogram as equal to the weight of a liter of water was a particularly brilliant way to ensure a standard value. It isn't, because of difficulties in making such a liter actually constant. The easy part is making sure they're at the same temperature and pressure (the triple point of water defines those). But they also have to have the same isotope ratio, they have to have the same impurities (or lack thereof), they have to have the same amount of dissolved gasses. Plus, getting the volume exact actually isn't trivial either. You might think, just make a cube 10cm on each side. But it's very hard to make a cube where all the sides are exactly 90 degrees apart. Any slight skew, and the volume changes, even if the sides are the perfect length. So even measuring volume precisely is very, very hard to do. Length is much easier to measure than volume. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law
 20th November 2018, 12:07 PM #19 Jimbo07 Illuminator     Join Date: Jan 2006 Posts: 3,683 Originally Posted by Ziggurat Length is much easier to measure than volume. Exactly. I just take out my tape measure, unzip my p... what? I was gonna say pencil case! __________________ This post approved by your local jPac (Jimbo07 Political Action Committee), also registered with Jimbo07 as the Jimbo07 Equality Rights Knowledge Betterment Action Group. Atoms in supernova explosion get huge business -- Pixie of key
 23rd November 2018, 10:52 AM #20 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Ziggurat Plus, getting the volume exact actually isn't trivial either. You might think, just make a cube 10cm on each side. But it's very hard to make a cube where all the sides are exactly 90 degrees apart. Any slight skew, and the volume changes, even if the sides are the perfect length. So even measuring volume precisely is very, very hard to do. Length is much easier to measure than volume. Can't you use trig? For example a triangle with sides with lengths 3u, 4u and 5u necessarily has a 90 degree angle. If the lengths are accurate then so is the angle. __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin Last edited by caveman1917; 23rd November 2018 at 10:54 AM.
 23rd November 2018, 01:50 PM #21 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by caveman1917 Can't you use trig? For example a triangle with sides with lengths 3u, 4u and 5u necessarily has a 90 degree angle. If the lengths are accurate then so is the angle. You can do reasonably well with determining angles afterwards. But how do you MAKE the angle precise? Especially if it's an interior angle, as it has to be for making a container for water. It's very, very hard to do at the level of precision we're talking about here. This new move to define the Kg in terms of Planck's constant isn't the first effort to make it artifact-independent. Previous efforts have tried to tie it to Avogadro's number. That effort basically used a sphere of isotopically pure silicon of precisely known volume so that you could in effect count the number of atoms in the sphere. The choice of a sphere wasn't arbitrary: it's actually easier to make a sphere of precise volume than a cube. The reason is that you don't need to worry about angles: just make sure its the same diameter no matter which way you spin it. You can't make a cube to the same level of precision. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law
 23rd November 2018, 02:41 PM #22 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Ziggurat You can do reasonably well with determining angles afterwards. But how do you MAKE the angle precise? Especially if it's an interior angle, as it has to be for making a container for water. It's very, very hard to do at the level of precision we're talking about here. This new move to define the Kg in terms of Planck's constant isn't the first effort to make it artifact-independent. Previous efforts have tried to tie it to Avogadro's number. That effort basically used a sphere of isotopically pure silicon of precisely known volume so that you could in effect count the number of atoms in the sphere. The choice of a sphere wasn't arbitrary: it's actually easier to make a sphere of precise volume than a cube. The reason is that you don't need to worry about angles: just make sure its the same diameter no matter which way you spin it. You can't make a cube to the same level of precision. Maybe you don't really need a container nor even a cube. You could put water in a larger container that's exactly filled up, submerge your 1 liter object (cube/sphere/...) and measure the water that got displaced instead. __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin
 23rd November 2018, 03:04 PM #23 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by caveman1917 Maybe you don't really need a container nor even a cube. You could put water in a larger container that's exactly filled up, submerge your 1 liter object (cube/sphere/...) and measure the water that got displaced instead. That's tricky too, because how do you separate that precise volume without spilling any, letting it get exposed to air, or leaving drops behind inside your valves? You can't expose it to air because then you need to worry about dissolved gasses. The level of precision involved here is mind boggling, even the slightest thing can screw it all up. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law
 23rd November 2018, 03:16 PM #24 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Ziggurat That's tricky too, because how do you separate that precise volume without spilling any, letting it get exposed to air, or leaving drops behind inside your valves? You can't expose it to air because then you need to worry about dissolved gasses. The level of precision involved here is mind boggling, even the slightest thing can screw it all up. Some of those problems are also going to exist with the container cube. Assume you have such a cube, how are you going to fill it up? Specifically, what is the water going to displace inside the cube? If it's a vacuum then the water will boil, if it's air then the water gets exposed to air. ETA: yeah nevermind about this paragraph, solution is trivial A possibility might be to have a deformable container, think something like a large container with a hole in the top with a balloon attached. As the 1 liter object gets submerged, the water goes into the balloon (expanding the balloon) and you detach the balloon which now has 1 liter of water in it. __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin Last edited by caveman1917; 23rd November 2018 at 03:25 PM.
 23rd November 2018, 03:54 PM #25 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by caveman1917 A possibility might be to have a deformable container, think something like a large container with a hole in the top with a balloon attached. As the 1 liter object gets submerged, the water goes into the balloon (expanding the balloon) and you detach the balloon which now has 1 liter of water in it. None of this is worth doing. Instead of making an incredibly precise volume of something else and then using that to measure the volume of water, just use the thing you made an incredibly precise volume of directly. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law
 23rd November 2018, 04:05 PM #26 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Ziggurat None of this is worth doing. Few things are. Quote: Instead of making an incredibly precise volume of something else and then using that to measure the volume of water, just use the thing you made an incredibly precise volume of directly. The point was to accurately get 1 liter of water though: Originally Posted by Ziggurat Plus, getting the volume exact actually isn't trivial either. You might think, just make a cube 10cm on each side. But it's very hard to make a cube where all the sides are exactly 90 degrees apart. Any slight skew, and the volume changes, even if the sides are the perfect length. So even measuring volume precisely is very, very hard to do. Length is much easier to measure than volume. __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin
 23rd November 2018, 04:53 PM #27 Blue Mountain Resident Skeptical Hobbit     Join Date: Jul 2005 Location: Waging war on woo-woo in Winnipeg Posts: 6,028 The point of a standard is to ensure everyone agrees on the definition. Now if I'm buying a sack of potatoes, I might not worry about a almost non-detectable difference between how the grower and the seller define a kilogram. But if I'm purchasing a potent drug where the difference between non-effective, effective, overdose and lethal may be on the order of micrograms, I want to be damned sure the lab making the drug knows precisely the value of that microgram. In that context, sloshing around a litre of water isn't going to cut it. __________________ The social illusion reigns to-day upon all the heaped-up ruins of the past, and to it belongs the future. The masses have never thirsted after truth. They turn aside from evidence that is not to their taste, preferring to deify error, if error seduce them. Gustav Le Bon, The Crowd, 1895 (from the French) Canadian or living in Canada? PM me if you want an entry on the list of Canadians on the forum.
 23rd November 2018, 05:13 PM #28 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Blue Mountain The point of a standard is to ensure everyone agrees on the definition. Now if I'm buying a sack of potatoes, I might not worry about a almost non-detectable difference between how the grower and the seller define a kilogram. But if I'm purchasing a potent drug where the difference between non-effective, effective, overdose and lethal may be on the order of micrograms, I want to be damned sure the lab making the drug knows precisely the value of that microgram. In that context, sloshing around a litre of water isn't going to cut it. You realize that drug companies have been doing just fine with the IPK standard up until today, right? I mean, I'm sure they're not all weighing their doses by going to Paris to take turns with the IPK artefact. __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin
23rd November 2018, 05:46 PM   #29
rjh01
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Originally Posted by Blue Mountain
The point of a standard is to ensure everyone agrees on the definition. Now if I'm buying a sack of potatoes, I might not worry about a almost non-detectable difference between how the grower and the seller define a kilogram. But if I'm purchasing a potent drug where the difference between non-effective, effective, overdose and lethal may be on the order of micrograms, I want to be damned sure the lab making the drug knows precisely the value of that microgram. In that context, sloshing around a litre of water isn't going to cut it.
Originally Posted by caveman1917
You realize that drug companies have been doing just fine with the IPK standard up until today, right? I mean, I'm sure they're not all weighing their doses by going to Paris to take turns with the IPK artefact.

Here is another video on the subject. Would have agreed with caveman1917 except they do specifically mention drugs in the video. I think the disagreement over the mass of a kilogram was what its 7th digit is. So a person might export a kilogram of a substance and the person who imports it might claim that it has a mass of only 0.999999 kilograms just because of the ambiguity of what a kilogram is.
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In future every country can build a machine that can weigh a kilogram and every such machine in the world will agree on the answer. Though I am sure they will test this just to be sure. Then every non standard method of finding mass will have to be calibrated with the new standard.
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Last edited by rjh01; 23rd November 2018 at 05:56 PM. Reason: Move a sentence so it makes sense

23rd November 2018, 06:51 PM   #30
casebro
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Originally Posted by rjh01
Here is another video on the subject. Would have agreed with caveman1917 except they do specifically mention drugs in the video. I think the disagreement over the mass of a kilogram was what its 7th digit is. So a person might export a kilogram of a substance and the person who imports it might claim that it has a mass of only 0.999999 kilograms just because of the ambiguity of what a kilogram is.
 YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website. I AGREE

....
+/- ONE microgram? or is that a nanogram? By an actual scale? How many of those in the commercial world?
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 23rd November 2018, 07:00 PM #31 casebro Penultimate Amazing     Join Date: Jun 2005 Posts: 17,817 Originally Posted by rjh01 ...... In future every country can build a machine that can weigh a kilogram and every such machine in the world will agree on the answer. Though I am sure they will test this just to be sure. Then every non standard method of finding mass will have to be calibrated with the new standard. Which would require a thermometer to measure the heat in the object to a micro-degree? No, wait. Since you need to check the temp of the object first, THEN add an exact amount of heat to it (measured in nano-joules? ) THEN check the temp to see how much the temp rose, and calculate the mass from there? So each of those instruments ought to be at least one magnitude more accurate than the desired result. Do those instruments exist in the kilogram +/- .1 microgram range today? __________________ It's hard to tell an intuician from a magician if you think that they are both pulling things out if their asses.
 23rd November 2018, 08:42 PM #32 Wolrab Illuminator   Join Date: Dec 2002 Posts: 4,669 Will there be more than 28 grams per ounce? I'm asking for a friend.... __________________ "Such reports are usually based on the sighting of something the sighters cannot explain and that they (or someone else on their behalf) explain as representing an interstellar spaceship-often by saying "But what else can it be?" as though thier own ignorance is a decisive factor." Isaac Asimov
 23rd November 2018, 08:47 PM #33 RecoveringYuppy Philosopher   Join Date: Nov 2006 Posts: 9,947 Originally Posted by Wolrab Will there be more than 28 grams per ounce? I'm asking for a friend.... Yes, Yes, many more.
 24th November 2018, 09:43 AM #34 Wolrab Illuminator   Join Date: Dec 2002 Posts: 4,669 Originally Posted by RecoveringYuppy Yes, Yes, many more. Duuuude! 28 grams to an ounce, the most recognized metric to English conversion in the USA. __________________ "Such reports are usually based on the sighting of something the sighters cannot explain and that they (or someone else on their behalf) explain as representing an interstellar spaceship-often by saying "But what else can it be?" as though thier own ignorance is a decisive factor." Isaac Asimov
 24th November 2018, 12:35 PM #35 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by caveman1917 You realize that drug companies have been doing just fine with the IPK standard up until today, right? I mean, I'm sure they're not all weighing their doses by going to Paris to take turns with the IPK artefact. Using the IPK standard doesn't require taking out the IPK artifact every time, it means using instruments whose calibration can be traced back to the IPK artifact. And the IPK artifact, while not perfect, was already a lot better than measuring a liter of water. It's the liter of water, not the IPK artifact, which doesn't suffice for drugs. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law Last edited by Ziggurat; 24th November 2018 at 12:36 PM.
 24th November 2018, 01:01 PM #36 caveman1917 Philosopher   Join Date: Feb 2015 Posts: 6,989 Originally Posted by Ziggurat Using the IPK standard doesn't require taking out the IPK artifact every time, it means using instruments whose calibration can be traced back to the IPK artifact. Exactly, so why would using the water standard require one to slosh around a liter of water? What's so special about the water standard that one can't use calibrated instruments as well? __________________ "Ideas are also weapons." - Subcomandante Marcos "We must devastate the avenues where the wealthy live." - Lucy Parsons "Let us therefore trust the eternal Spirit which destroys and annihilates only because it is the unfathomable and eternal source of all life. The passion for destruction is a creative passion, too!" - Mikhail Bakunin
 24th November 2018, 02:12 PM #37 RecoveringYuppy Philosopher   Join Date: Nov 2006 Posts: 9,947 Originally Posted by Blue Mountain The point of a standard is to ensure everyone agrees on the definition. Now if I'm buying a sack of potatoes, I might not worry about a almost non-detectable difference between how the grower and the seller define a kilogram. But if I'm purchasing a potent drug where the difference between non-effective, effective, overdose and lethal may be on the order of micrograms, I want to be damned sure the lab making the drug knows precisely the value of that microgram. In that context, sloshing around a litre of water isn't going to cut it. "Sloshing water" around will cut it, because errors are relative, not absolute. Let's say a drug company has a standard 1 Kg reference mass that's off by a full gram. That's 1 part in 1,000 or .1%. That difference doesn't lead to a full gram mistake in their definition of the microgram. It leads to a single nanogram discrepancy in their definition. That's no problem and it's 5 or 6 orders of magnitude greater than other errors being discussed in this thread. Last edited by RecoveringYuppy; 24th November 2018 at 02:42 PM.
 24th November 2018, 03:41 PM #38 Ziggurat Penultimate Amazing     Join Date: Jun 2003 Posts: 46,157 Originally Posted by caveman1917 Exactly, so why would using the water standard require one to slosh around a liter of water? What's so special about the water standard that one can't use calibrated instruments as well? You could. But in order to do that calibration, you're still going to need a liter of water sloshing around, because that's what the water standard is. And calibrating against a liter of water is a lot harder to do than calibrating against the IPK standard artifact, and a lot less accurate as well. Even if you don't have to do it very often, you will still have lost accuracy. __________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law
 24th November 2018, 06:57 PM #39 lpetrich Muse   Join Date: Feb 2007 Posts: 762 pound avoirdupois -- the ordinary English-unit pound, defined in 1963 to be exactly 453.59237 grams. The US pound was earlier defined to be 453.5924277 g, and the Imperial pound was earlier approximately 453.592338 g. The density of water was a good idea in theory, something universally available, but it proved impractical for getting a lot of precision. So that's why we were stuck with platinum cylinders until recently. The IPK is used as a reference for some secondary mass standards, also platinum-iridium cylinders, and these are in turn used as references for more widely-used standards. I think that with this redefinition, the IPK will join the secondary mass standards. The most successful measurement of mass with the new definition has been with the Kibble balance, formerly the Watt balance. It measures how much electric current is needed to balance the gravitational force on some massive object. That object's mass is then calculated with the help of the acceleration of gravity at the balance's location. The electric current flows through a coil in a magnetic field, and that field's value is found by wiggling the balance and finding out how much induced voltage it makes. Voltage is measured using the Josephson effect as a standard, making it proportional to h/e. Current is measured using voltage and resistance, and the latter is measured using the quantum Hall effect as a standard. Thus giving (h/e) / (h/e^2) = e The balance effectively measures (voltage) * (current) ~ (electrical power) ~ h. Thus its earlier name.
 24th November 2018, 07:28 PM #40 lpetrich Muse   Join Date: Feb 2007 Posts: 762 The seven SI base units are the meter, kilogram, second, ampere, mole, kelvin, and candela. They started out with separate physical realizations, but they now have only one. The second is now the base unit for all the others. The meter was originally 10-7 of the Earth's pole-to-equator distance, then it became the length of a platinum bar in Paris, then a multiple of the wavelength of light from a certain electronic transition in krypton-86, and then in terms of the second by fixing the speed of light in a vacuum. The second was originally 1/86,400 of a solar day, later clarified to the mean solar day. It then became some small fraction of some specified year, and finally a multiple of the period of radio waves from the ground-state hyperfine transition of cesium-133. The mole's name is short for "gram molecular weight". It is defined with Avogadro's number, the number of atomic mass units in a gram. The amu was originally the mass of a hydrogen atom, then 1/16 the mass of an oxygen atom, then 1/12 the mass of a carbon-12 atom. Avogadro's number is now fixed, making the amu a fixed number of kilograms. The kelvin was originally a degree Celsius, defined as 0 = melting point of water and 100 = boiling point of water at sea-level pressure. The Kelvin scale's zero point is absolute zero, and the kelvin's size became 1/273.16 the temperature of the triple point of water. The kelvin is now defined in terms of energy by fixing Boltzmann's constant. Visible-light luminosity standards were originally lamps with specified construction, and the candela was originally the blackbody luminosity of melting-point platinum, and then some energy flux. It's something like what happened with energy: when different kinds of energy were shown to be interconvertible, they were given the same units.

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