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spike420211
Forum Yoda
Joined: 25 Apr 2007
Posts: 4057
Location: Pennsylvania, where poker is now LEGAL!
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 Posted: Tue Oct 27, 2009 6:01 pm Post subject: a weighty issue, no doubt |
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OK.
I was taught in high school, and later in electronics school [high school with ashtrays], that a Kilogram equals 1 liter, or 1000 cubic centimeters, of water.
[de-ionized, measured at like 1 deg. centigrade, if u want, I spose I could Google the exact specs.]
So, even though the scientific community decided on a constant defined by a certain wavelength of light, they still use a platinum cylinder to define a Kilogram.
If we can exactly define a meter,
then we can exactly define a 10 cm X 10cm X 10cm box,
and pour water into it,
and then weigh it.
Yes, I know metrology is more complicated than THIS, BUT WTF?
Check out the triple bell jars they use to protect the cylinder...
http://www.npr.org/templates/story/story.php?storyId=112003322 |
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jeffr8
Inspector Gadget
Joined: 22 Oct 2006
Posts: 3637
Location: On a boat
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| Posted: Tue Oct 27, 2009 6:07 pm Post subject: |
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^ the reason the kilo is a little lighter |
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Flying_Kiwi
Bird of Mystery
Joined: 03 Sep 2006
Posts: 8457
Location: Spewing bonus $
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| Posted: Tue Oct 27, 2009 6:11 pm Post subject: |
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| Drugs: teaching inner city youths the metric system. |
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telebob
Royal Flush
Joined: 17 Oct 2006
Posts: 767
Location: Close enough to see Sparks
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| Posted: Tue Oct 27, 2009 8:49 pm Post subject: |
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| Not a weighty issue, imo, tho it could be a massive one. |
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templar rage
Message Board Junkie
Joined: 30 Dec 2008
Posts: 1551
Location: Rhode Island
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| Posted: Tue Oct 27, 2009 9:37 pm Post subject: |
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| telebob wrote: |
| Not a weighty issue, imo, tho it could be a massive one. |
Does the fact that I got this joke make me a nerd? |
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HuJwang
Forum Blight
Joined: 20 Aug 2006
Posts: 9197
Location: Halifax, NS
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| Posted: Wed Oct 28, 2009 4:23 pm Post subject: Re: a weighty issue, no doubt |
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| spike420211 wrote: |
If we can exactly define a meter,
then we can exactly define a 10 cm X 10cm X 10cm box,
and pour water into it,
and then weigh it. |
there's a difference between defining something exactly and building something exactly. not only do you have to build a perfectly precise, incompressable box, but you have to ensure that there is exactly 1L of water inside, which requires that you ensure the pressure and temperature stay perfectly constant and uniform. |
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francois8
Message Board Junkie
Joined: 10 Jun 2008
Posts: 3920
Location: getting bent over the bubble
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| Posted: Wed Oct 28, 2009 4:41 pm Post subject: |
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Lengths of material change readily with temperature. Mass only changes with chemical reactions with air / water that results in physical removal or addition of molecules.
I believe that 1 L of water = 1 kg at its maximum density which is 4C for water... Almost every other material continues to get denser as you cool it more, but the maximum density at 4C is why ice floats, ponds freeze from top down, and pretty much allowed life to develop.
Its funny to me that they lock the one kg up in such a secure location to protect it... then they're surprised that the unprotected ones don't match it after 120 years? If they weren't different, one would have to ask why they went through all that triple bell jar effort. |
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spike420211
Forum Yoda
Joined: 25 Apr 2007
Posts: 4057
Location: Pennsylvania, where poker is now LEGAL!
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| Posted: Wed Oct 28, 2009 8:05 pm Post subject: Re: a weighty issue, no doubt |
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| HuJwang wrote: |
| spike420211 wrote: |
If we can exactly define a meter,
then we can exactly define a 10 cm X 10cm X 10cm box,
and pour water into it,
and then weigh it. |
there's a difference between defining something exactly and building something exactly. not only do you have to build a perfectly precise, incompressable box, but you have to ensure that there is exactly 1L of water inside, which requires that you ensure the pressure and temperature stay perfectly constant and uniform. |
with the mathematical constant [the wavelength of Krypton, used for the meter] you can repeat experiments, even start from scratch, and get pretty damn close. Reliance upon a physical object [the cylinder] can cause drift from an accepted standard, an exaggerated representation of this being the pic in jeffr8's post.
I'm sure this all sounds nit-picky, but when one talks of terms involving precision [certain # of mg. in a painkiller dose, or 0.01's of a mm in interchangable parts] or economies of scale [millions of liters of gasoline]
then all this increases in importance. |
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