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http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html
--
~Mike
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Mike Raiford wrote:
> http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html
...and here I was thinking that 12g of C12 was *defined as* one mole of
C12 atoms...
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Invisible <voi### [at] dev null> wrote:
> Mike Raiford wrote:
> > http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html
> ...and here I was thinking that 12g of C12 was *defined as* one mole of
> C12 atoms...
Hence the definition of 'mole' depends on the definition of 'kilogram',
not the other way around.
--
- Warp
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Mike Raiford <"m[raiford]!at"@gmail.com> wrote:
> http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html
Why can't the kilogram be defined as the weight of exactly 1 litre of
pure water at a certain temperature? After all, that has been the de-facto
definition for forever.
--
- Warp
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On 10/12/09 10:17, Warp wrote:
> Mike Raiford<"m[raiford]!at"@gmail.com> wrote:
>> http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html
>
> Why can't the kilogram be defined as the weight of exactly 1 litre of
> pure water at a certain temperature? After all, that has been the de-facto
> definition for forever.
Perhaps they could _change_ the definition to that, but I'm willing to
bet that it's off by a bit from the current definition.
--
A tautology is a thing which is tautological.
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Neeum Zawan <m.n### [at] ieeeorg> wrote:
> Perhaps they could _change_ the definition to that, but I'm willing to
> bet that it's off by a bit from the current definition.
AFAIK kilogram *was* originally defined as the weight of 1 liter of water,
but for whatever reason they changed it to the weight of a specific object
(I really can't understand why).
According to wikipedia, one liter of pure water at 4 degrees celsius (the
standard temperature for measuring SI units) is 0.9999720 kilograms.
If they changed the definition of kilogram back to its original form, the
change would be less than 0.003% from the currently accepted value. Would
that be a huge catastrophe?
--
- Warp
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Warp wrote:
> According to wikipedia, one liter of pure water at 4 degrees celsius (the
> standard temperature for measuring SI units) is 0.9999720 kilograms.
It may be that it's too difficult to measure "pure water" at "exactly 4
degrees celsius" for modern measurement precision.
Plus, of course, if you make *everything* circular, then you have nothing.
If a kilogram is the weight (well, mass) of a liter of water, and a liter is
1000 cubic centimeters, and a centimeter is the length of one gram of carbon
atoms lined up (or some such) then the whole thing falls down.
Given that a cm is defined in terms of the speed of light, and time is
defined in terms of a cesium atom at rest at 0K, I guess we already have
unusable base metrics, tho.
> If they changed the definition of kilogram back to its original form, the
> change would be less than 0.003% from the currently accepted value. Would
> that be a huge catastrophe?
Only for scientists working on 15 digits of precision in their scientific
experiments. Kind of like "would it really make a difference if we skipped a
leap-second every 3 to 5 years?"
--
Darren New, San Diego CA, USA (PST)
I ordered stamps from Zazzle that read "Place Stamp Here".
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>> ...and here I was thinking that 12g of C12 was *defined as* one mole of
>> C12 atoms...
>
> Hence the definition of 'mole' depends on the definition of 'kilogram',
> not the other way around.
Ah, I see.
Couldn't they just reverse it? I mean, just say that 1 Kg = the mass of
XXX C12 atoms?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > According to wikipedia, one liter of pure water at 4 degrees celsius (the
> > standard temperature for measuring SI units) is 0.9999720 kilograms.
> It may be that it's too difficult to measure "pure water" at "exactly 4
> degrees celsius" for modern measurement precision.
Not more difficult than measuring the exact speed of light (which is needed
to define the unit of length) or an exact magnetic force (which is needed to
define the unit of electric current).
> Plus, of course, if you make *everything* circular, then you have nothing.
> If a kilogram is the weight (well, mass) of a liter of water, and a liter is
> 1000 cubic centimeters, and a centimeter is the length of one gram of carbon
> atoms lined up (or some such) then the whole thing falls down.
But a centimeter is not defined like that. It's defined from the speed of
light in vacuum. There's no circle.
> Given that a cm is defined in terms of the speed of light, and time is
> defined in terms of a cesium atom at rest at 0K, I guess we already have
> unusable base metrics, tho.
Unusable base metrics?
> > If they changed the definition of kilogram back to its original form, the
> > change would be less than 0.003% from the currently accepted value. Would
> > that be a huge catastrophe?
> Only for scientists working on 15 digits of precision in their scientific
> experiments. Kind of like "would it really make a difference if we skipped a
> leap-second every 3 to 5 years?"
Given that the object which is currently the measurement of 1 kg changes
weight every time it's measured, does it really matter? It would simply be
one more change, but then it would be fixed, and that's it.
--
- Warp
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Warp wrote:
> But a centimeter is not defined like that. It's defined from the speed of
> light in vacuum. There's no circle.
Yes, I saw that.
> Unusable base metrics?
0K is unreachable even in theory.
> Given that the object which is currently the measurement of 1 kg changes
> weight every time it's measured, does it really matter? It would simply be
> one more change, but then it would be fixed, and that's it.
True. I don't know how they work it now.
--
Darren New, San Diego CA, USA (PST)
I ordered stamps from Zazzle that read "Place Stamp Here".
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