Metric system in crisis
Kevin Gowen
http://www.wisinfo.com/thereporter/news/archive/opinion_10640925.shtml
In 1889, the International Committee on Weights and Measures defined the
kilogram by the weight of a cylinder cast in England of platinum and
iridium. This standard kilogram is secured in a heavily guarded chateau
outside Paris. It is inspected once a year by the only three people who have
keys.
Here’s the problem: Yearly inspections have apparently shown that the
kilogram cylinder has lost weight, approximately 50 micrograms. That’s less
than the weight of a grain of salt, but it’s plenty to send the world of
weights and measures into an epic tizzy. Quantities of human ingenuity are
being expended to re-adjust the kilo and render it eternally precise. For
example, German scientists are working in Russian nuclear facilities to
produce a perfectly round 1-kilo sphere of silicon. Then, by knowing the
number of atoms in the sphere and their distance from one another ...
--
Kevin Gowen
Travers Naran
Except that the Imperial ounce and pound were redefined to correlate to
the kilogram. D'oh!
--
---------------------------------------------------------------------------
Travers Naran | Visit the SFTV Science Blunders
F/T Programmer,P/T Meddler In Time&Space | Hall of Infamy!
New Westminster, British Columbia, |
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"Stand Back! I'm a programmer!" | ** UPDATED 9-Apr-2002 **
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Kevin Gowen
> Kevin Gowen wrote:
>
>> Soon yall will have to learn what an ounce is.
>> http://www.wisinfo.com/thereporter/news/archive/opinion_10640925.shtml
>>
>> In 1889, the International Committee on Weights and Measures defined
>> the kilogram by the weight of a cylinder cast in England of platinum
>> and iridium. This standard kilogram is secured in a heavily guarded
>> chateau outside Paris. It is inspected once a year by the only three
>> people who have keys.
>> Here’s the problem: Yearly inspections have apparently shown that the
>> kilogram cylinder has lost weight, approximately 50 micrograms.
>> That’s less than the weight of a grain of salt, but it’s plenty to
>> send the world of weights and measures into an epic tizzy.
>> Quantities of human ingenuity are being expended to re-adjust the
>> kilo and render it eternally precise. For example, German scientists
>> are working in Russian nuclear facilities to produce a perfectly
>> round 1-kilo sphere of silicon. Then, by knowing the number of atoms
>> in the sphere and their distance from one another ...
>
> Except that the Imperial ounce and pound were redefined to correlate
> to
> the kilogram. D'oh!
The last I heard, the Avoirdupois pound was defined as being the weight of
27.7015 cubic inches of distilled water at 62 degrees F with the barometer
being at 30 inches. When did the redefinition you claim take place?
--
Kevin Gowen
Greg Macdonald
<kgowen...@myfastmail.com> spake:
In 1893 according to the U.S. National Bureau of Standards.
http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf
Brett Robson
1. avoirdupois pound is not an imperial pound
2. your definition is pound-force not pound
3. your definition is /less/ accurate than using a standard object
(perhaps this would be an interesting homework project for you. Discuss a
practical way of maintaining as constant the 3 variables, volume, temp, and
atmospheric
pressure. Be sure to mention the effect of measurement on values)
3. how can a measurement system define something without any outside references?
if you don't understand any of the above please refer to an introductory physics
text.
> When did the redefinition you claim take place?
>
Avoirdupois? IIRC in the US 1890s.
"Crispin Sartwell teaches philosophy at the Maryland Institute College of Art."
Christ Gowan, I've only just got my workstation cleaned up from yesterday's
accident.
---
"he [John Ashcroft] deliberately left Jesus out of office prayers to avoid
offending non-Christians." - Ben Shapiro 27/2/2003
Silvio Franke
Kevin Gowen schrieb:
> For example, German scientists are working in Russian nuclear
> facilities [...]
Do you really think they're working on a "perfectly round 1-kilo sphere
of silicon"?
HarrrHarrr (= a devilish laughter with a German accent, while at the
same time stroking the white cat on my arm)
Silvio
-------------------------------------------------
Sometimes I feel the strong urge to march east...
Eric Takabayashi
> Soon yall will have to learn what an ounce is.
> http://www.wisinfo.com/thereporter/news/archive/opinion_10640925.shtml
>
> In 1889, the International Committee on Weights and Measures defined the
> kilogram by the weight of a cylinder cast in England of platinum and
> iridium. This standard kilogram is secured in a heavily guarded chateau
> outside Paris. It is inspected once a year by the only three people who have
> keys.
> Here’s the problem: Yearly inspections have apparently shown that the
> kilogram cylinder has lost weight, approximately 50 micrograms.
But how would they know?
Brett Robson
>
>Kevin Gowen wrote:
>
>> Soon yall will have to learn what an ounce is.
>> http://www.wisinfo.com/thereporter/news/archive/opinion_10640925.shtml
>>
>> In 1889, the International Committee on Weights and Measures defined the
>> kilogram by the weight of a cylinder cast in England of platinum and
>> iridium. This standard kilogram is secured in a heavily guarded chateau
>> outside Paris. It is inspected once a year by the only three people who have
>> keys.
>> Here’s the problem: Yearly inspections have apparently shown that the
>> kilogram cylinder has lost weight, approximately 50 micrograms.
>
>But how would they know?
>
They don't, that's an estimate.
Curt Fischer
Brett Robson wrote:
> >
> >The last I heard, the Avoirdupois pound was defined as being the weight of
> >27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> >being at 30 inches.
>
> 1. avoirdupois pound is not an imperial pound
You're right here. Congratulations. Don't let it go to your head
though....
> 2. your definition is pound-force not pound
A pound force is a pound. So what are you talking about?
> 3. your definition is /less/ accurate than using a standard object
> (perhaps this would be an interesting homework project for you. Discuss a
> practical way of maintaining as constant the 3 variables, volume, temp, and
> atmospheric
> pressure. Be sure to mention the effect of measurement on values)
Umm, why couldn't you use any number of commercially available devices
to maintain the desired temperature, volume, and pressure?
> 3. how can a measurement system define something without any outside references?
I don't know. You tell me. If you could include why it is relevant to
this discussion, that would be good too.
> if you don't understand any of the above please refer to an introductory physics
> text.
Could you let me know which introductory physics text you referenced
before writing your post?
--
Curt Fischer
Michael Cash
<silvio...@unibw-muenchen.de> belched the alphabet and kept on
going with:
>
>
>Kevin Gowen schrieb:
>> For example, German scientists are working in Russian nuclear
>> facilities [...]
>
>Do you really think they're working on a "perfectly round 1-kilo sphere
>of silicon"?
American scientists have been making perfectly round silicon spheres
weighing about 10 pounds for several years now. Haven't you ever seen
an American porno film?
--
Michael Cash
"I am Elmer J. Fudd, millionaire. I own a mansion and a yacht."
Elmer J. Fudd
Millionaire
Kevin Wayne Williams
[inaccurate stuff undermining a sound point]
You might try referring your detractors to the Mendenhall Order of 1893,
which did legally redefine the yard and the pound to be derived from
metric equivalents, and all derived units, by extension, to have precise
metric equivalents. It was revised in 1959, but all units of measure in
the US have been legally based on the metric system for 110 years.
http://www.sizes.com/units/yard.htm gives a good summary.
KWW
Ken
>
> Brett Robson wrote:
>
>>>The last I heard, the Avoirdupois pound was defined as being the weight of
>>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
>>>being at 30 inches.
>>
>>1. avoirdupois pound is not an imperial pound
>
> You're right here. Congratulations. Don't let it go to your head
> though....
>
>>2. your definition is pound-force not pound
>
> A pound force is a pound. So what are you talking about?
Well, Kevin's obsolete definition might have been better if he had said
*mass* instead of "*weight* of 27.7015 cubic inches...".
One might speak of weightlessness, e.g. in orbit. It wouldn't occur to an
astronaut, however, to say that he/she's massless... Astronauts composed
of non-baryonic matter, and hence travelling at light speed, would be an
interesting concept, indeed...
For those confused about these notions, the pound-force is the weight, or
*force* exerted by a pound of mass subjected to an acceleration of 1G; as
such, its expression in SI units would be in Newtons.
The pound, OTOH, is a unit of *mass*, and would be expressed in SI units
in Kilograms.
>>3. your definition is /less/ accurate than using a standard object
>> (perhaps this would be an interesting homework project for you.
>> Discuss a practical way of maintaining as constant the 3 variables,
>> volume, temp, and atmospheric pressure. Be sure to mention the
>> effect of measurement on values)
>
> Umm, why couldn't you use any number of commercially available devices
> to maintain the desired temperature, volume, and pressure?
First, because mass definitions involving a measurement of pressure
might be circular, as the standard pressure definition relies on mass,
acceleration and surface units... (Hint: how is the Pascal defined?)
Second, because there's no practical way to measure and regulate the
volume, temperature and pressure with the required precision.
The Pt+Ir mass references have an estimated error in the 10**-9 to
10**-8 range, which is the major reason these seemingly quaint objects
are still used, well, as mass references...
There's no better mass reference system known as of yet, even though
some new ideas are being investigated -- e.g. the Avogadro crystal
lattice approach based on accurately estimating the number of Si
atoms in a "perfect" sphere, whose dimensions are controlled by
interferometry.
>>if you don't understand any of the above please refer to an introductory
>>physics text.
>
> Could you let me know which introductory physics text you referenced
> before writing your post?
*Any* decent high-school physics text should have made clear the
fundamental difference between weight -- e.g. pound-force -- and mass
-- e.g. pound -- units... Whether the difference will be understood
by all the students is another matter, of course.
Kevin Wayne Williams
> *Any* decent high-school physics text should have made clear the
> fundamental difference between weight -- e.g. pound-force -- and mass
> -- e.g. pound -- units... Whether the difference will be understood
> by all the students is another matter, of course.
What the hell ever happened to slugs? I remember being taught pounds for
weight, and slugs for mass.
KWW
Kevin Gowen
Slugs were taught at least as recently as 1993 at my high school. However,
they were taught as a "by the way" during the discussion of the difference
between mass and weight. The metric system was used for all problems.
--
Kevin Gowen
John W.
>
> American scientists have been making perfectly round silicon spheres
> weighing about 10 pounds for several years now. Haven't you ever seen
> an American porno film?
>
Completely porn free, unfortunately, and really, really funny in a
stupid-move way.
John W.
Greg Macdonald
>On Tue, 10 Jun 2003 17:46:04 +0900, Eric ...
>>
>>Kevin Gowen wrote:
>>
>>> Soon yall will have to learn what an ounce is.
>>> http://www.wisinfo.com/thereporter/news/archive/opinion_10640925.shtml
>>>
>>> In 1889, the International Committee on Weights and Measures defined the
>>> kilogram by the weight of a cylinder cast in England of platinum and
>>> iridium. This standard kilogram is secured in a heavily guarded chateau
>>> outside Paris. It is inspected once a year by the only three people who have
>>> keys.
>>> Here’s the problem: Yearly inspections have apparently shown that the
>>> kilogram cylinder has lost weight, approximately 50 micrograms.
>>
>>But how would they know?
>>
>
>They don't, that's an estimate.
I believe they check the copies of the official cylinder against it
from time to time, and lately the copies have been consistently
'over', implying that either they are all over by the same amount, or
that the official cylinder is undermassed.
Curt Fischer
Ken wrote:
>
> Curt Fischer wrote:
> >
> > Brett Robson wrote:
> >
> >>>The last I heard, the Avoirdupois pound was defined as being the weight of
> >>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> >>>being at 30 inches.
> >>
> >>1. avoirdupois pound is not an imperial pound
> >
> > You're right here. Congratulations. Don't let it go to your head
> > though....
> >
> >>2. your definition is pound-force not pound
> >
> > A pound force is a pound. So what are you talking about?
>
> Well, Kevin's obsolete definition might have been better if he had said
> *mass* instead of "*weight* of 27.7015 cubic inches...".
But since the pound has historically been a unit of force, it is
definitely better to speak of "weight".
> One might speak of weightlessness, e.g. in orbit. It wouldn't occur to an
> astronaut, however, to say that he/she's massless... Astronauts composed
> of non-baryonic matter, and hence travelling at light speed, would be an
> interesting concept, indeed...
>
> For those confused about these notions, the pound-force is the weight, or
> *force* exerted by a pound of mass subjected to an acceleration of 1G; as
> such, its expression in SI units would be in Newtons.
> The pound, OTOH, is a unit of *mass*, and would be expressed in SI units
> in Kilograms.
According to every technical book I have ever used, the pound is a unit
of force. Ergo, pounds measure weight. Kilograms measure mass. This
is the reason that, in English (Sepponian) units, there is a no
non-unity non-dimensionless constant called gc (g sub c), which relates
force to mass. Here's a quick review for those of you having
difficulty:
http://gems.mines.edu/~mckinnon/DCGN209/Handouts/gc%20summary.pdf
Further evidence that the pound is a unit of force comes from
established terms like "ft-lbs", which I hope everyone will agree is a
unit of torque, not some mysterious unit of dimension (mass)x(length).
You might also want to check out what a "slug" is.
>
> >>3. your definition is /less/ accurate than using a standard object
> >> (perhaps this would be an interesting homework project for you.
> >> Discuss a practical way of maintaining as constant the 3 variables,
> >> volume, temp, and atmospheric pressure. Be sure to mention the
> >> effect of measurement on values)
> >
> > Umm, why couldn't you use any number of commercially available devices
> > to maintain the desired temperature, volume, and pressure?
>
> First, because mass definitions involving a measurement of pressure
> might be circular, as the standard pressure definition relies on mass,
> acceleration and surface units... (Hint: how is the Pascal defined?)
Yes, but the definition under discussion here was not a definition of
mass. Ergo, no tautology. Your points about accuracy are well-taken; I
do understand that there were reasons that the weights and measures
people adopted the Pt-Ir standard. But if 1893 levels of precision are
what we're talking about, then the devices today would perform
admirably.
Oh, I see, wait...Brent may have misinterpreted as serious Kevin's
suggestion that we return to English units!
> Second, because there's no practical way to measure and regulate the
> volume, temperature and pressure with the required precision.
> The Pt+Ir mass references have an estimated error in the 10**-9 to
> 10**-8 range, which is the major reason these seemingly quaint objects
> are still used, well, as mass references...
If we updated the definition to be the weight of a certain volume of
liquid water at its triple point, wouldn't that take care of the
temperature and pressure problem? How hard is it to measure volume
precisely?
> There's no better mass reference system known as of yet, even though
> some new ideas are being investigated -- e.g. the Avogadro crystal
> lattice approach based on accurately estimating the number of Si
> atoms in a "perfect" sphere, whose dimensions are controlled by
> interferometry.
What is the current uncertainty in Avogadro's number? Why can't the
standard unit of mass be the nucleus of one atom of carbon-12, which
already has an atomic mass of 12 amu by definition.
--
Curt Fischer
Kevin Wayne Williams
> According to every technical book I have ever used, the pound is a unit
> of force. Ergo, pounds measure weight.
Strangely enough, that 1893 measure specifically defined a pound as a
unit of mass. So far as I can tell, pounds legally measure mass, but
scientifically measure weight. Something like that old UL about pi being
equal to 3 in Indiana.
KWW
Gene Nygaard
> Curt Fischer wrote:
> >
> > Brett Robson wrote:
> >
> >>>The last I heard, the Avoirdupois pound was defined as being the weight of
> >>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> >>>being at 30 inches.
> >>
> >>1. avoirdupois pound is not an imperial pound
> >
> > You're right here. Congratulations. Don't let it go to your head
> > though....
> >
> >>2. your definition is pound-force not pound
> >
> > A pound force is a pound. So what are you talking about?
>
> Well, Kevin's obsolete definition might have been better if he had said
> *mass* instead of "*weight* of 27.7015 cubic inches...".
It wouldn't have been anything different if he had done so.
A troy ounce is a unit of weight, isn't it? But the units in the troy
system of weights are always units of mass, never units of force.
There is no troy ounce force, never has been.
> One might speak of weightlessness, e.g. in orbit. It wouldn't occur to an
> astronaut, however, to say that he/she's massless... Astronauts composed
> of non-baryonic matter, and hence travelling at light speed, would be an
> interesting concept, indeed...
>
> For those confused about these notions, the pound-force is the weight, or
> *force* exerted by a pound of mass subjected to an acceleration of 1G; as
> such, its expression in SI units would be in Newtons.
So how much acceleration is that?
There is an official acceleration for the purpose of defining grams
force, adopted by the CGPM in 1901 for exactly that purpose (this is a
concept of metrology, not of physics, something which serves no
purpose other than to define units of force based on units of mass):
980.665 cm/s².
But there is no official value for the definition of pounds force.
Few high school and fewer college textbooks use pounds at all any
more, even in the United States.
Furthermore, a few these textbooks which do mention pounds (even if
they rarely or never actually use them) are now being written by
people so poorly educated themselves that several of them claim that
pounds are not units of mass. E.g., Halliday, Resnick, and Walker
(1997 and a later one too). Of course, if you give a couple of
octagenarians an ego boost and a token royalty to keep their names on
the book, while turning it over to an entertainment columnist, with
editors more interested in pretty pictures and colored text than in
the written content, it's no surprise if what you end up with is a
farce.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
Gene Nygaard
> Brett Robson wrote:
>
> > >
> > >The last I heard, the Avoirdupois pound was defined as being the weight of
> > >27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> > >being at 30 inches.
> >
> > 1. avoirdupois pound is not an imperial pound
>
> You're right here. Congratulations. Don't let it go to your head
> though....
>
> > 2. your definition is pound-force not pound
>
> A pound force is a pound. So what are you talking about?
No, a pound force is a recent spinoff from the pound, which has always
been a unit of mass.
So new, in fact, that the pound force is uniquely idenitifed by that
name as the one based on the avoirdupois pound, the only one of all
the hundreds of different pounds used at various places and times
throughout history that has spawned a unit of force that has seen any
significant use.
For example, unlike pounds avoirdupois and unlike kilograms, the troy
pounds and troy ounces are always units of mass--there are no troy
pounds force or troy ounces force. Consider the other pounds still in
use, especially informally, in many different places in Latin
America--the ones redefined back in the 19th century to replace many
different old pounds, the ones defined as exactly 500 g or half a
kilogram. Units of mass, of course.
Pounds are, since a 1959 international agreement, by definition
exactly 0.45359237 kg. We no longer have independent standards for a
pound. In the United States, for the 66 years prior to that
international agreement, our pound had been defined as a slightly
different exact fraction of a kilogram.
Pound force, OTOH, don't even have an official definition.
As the newcomer, the pound force should be identified as such, and
should use a symbol to distinguish it from the normal pounds as units
of mass. American Society for Testing and Materials, Standard for
Metric Practice, E 380-79, ASTM 1979:
3.4.1.4 The use of the same name for units of force
and mass causes confusion. When the non-SI units
are used, a distinction should be made between force
and mass, for example, lbf to denote force in
gravimetric engineering units and lb for mass.
> > 3. your definition is /less/ accurate than using a standard object
> > (perhaps this would be an interesting homework project for you. Discuss a
> > practical way of maintaining as constant the 3 variables, volume, temp, and
> > atmospheric
> > pressure. Be sure to mention the effect of measurement on values)
>
> Umm, why couldn't you use any number of commercially available devices
> to maintain the desired temperature, volume, and pressure?
You can't measure the volume to the precision you can compare the mass
to the standard kilogram.
It is very difficult to keep the temperature throughout the water all
the same, and not fluctuating enough to be anywhere near the precision
you can get with a balance.
Gene Nygaard
Brett Robson
>
>
>
>Brett Robson wrote:
>
>> >
>> >The last I heard, the Avoirdupois pound was defined as being the weight of
>> >27.7015 cubic inches of distilled water at 62 degrees F with the barometer
>> >being at 30 inches.
>>
>> 1. avoirdupois pound is not an imperial pound
>
>You're right here. Congratulations. Don't let it go to your head
>though....
>
>> 2. your definition is pound-force not pound
>
>A pound force is a pound.
... when gravity equals exactly 1. Gravity is not constant in the universe or
even on the surface of the earth.
>
>> 3. your definition is /less/ accurate than using a standard object
>> (perhaps this would be an interesting homework project for you. Discuss a
>> practical way of maintaining as constant the 3 variables, volume, temp, and
>> atmospheric
>> pressure. Be sure to mention the effect of measurement on values)
>
>Umm, why couldn't you use any number of commercially available devices
>to maintain the desired temperature, volume, and pressure?
Firstly water is notoriously difficult to keep at a constant temp. Secondly
these 3 factors are all related to each other. Increase one and you have to
decrease the other two.
>
>>3. how can a measurement system define something without any outside references?
>
>I don't know. You tell me. If you could include why it is relevant to
>this discussion, that would be good too.
Sorry, I thought it was obvious. Kevin's definition uses 3 measurements which
are defined elsewhere. This is not as much a definition as a conversion between
units.
>
>>if you don't understand any of the above please refer to an introductory physics
>> text.
>
>Could you let me know which introductory physics text you referenced
>before writing your post?
>
I didn't. As phyics is all about measurement of the physically world then if
your introductory physics book did not include an extensive section on units of
measurement then I suggest you get a new book.
Brett Robson
>
>Firstly water is notoriously difficult to keep at a constant temp. Secondly
>these 3 factors are all related to each other. Increase one and you have to
>decrease the other two.
>
Thirdly you can't measure something without changing it. (Is this Schrodinger?)
Silvio Franke
Michael Cash schrieb:
>
> On Tue, 10 Jun 2003 08:16:53 +0200, Silvio Franke
> <silvio...@unibw-muenchen.de> belched the alphabet and kept on
> going with:
>
> >
> >
> >Kevin Gowen schrieb:
> >> For example, German scientists are working in Russian nuclear
> >> facilities [...]
> >
> >Do you really think they're working on a "perfectly round 1-kilo sphere
> >of silicon"?
>
> American scientists have been making perfectly round silicon spheres
> weighing about 10 pounds for several years now. Haven't you ever seen
> an American porno film?
It is a merit of the soldiers of our US-partner-battalion in
Schweinfurt, that I was able to see some...
Ken
>
> Ken wrote:
>
>>Curt Fischer wrote:
>>
>>>Brett Robson wrote:
>>>
>>>
>>>>>The last I heard, the Avoirdupois pound was defined as being the weight of
>>>>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
>>>>>being at 30 inches.
>>>>
>>>>1. avoirdupois pound is not an imperial pound
>>>
>>>You're right here. Congratulations. Don't let it go to your head
>>>though....
>>>
>>>
>>>>2. your definition is pound-force not pound
>>>
>>>A pound force is a pound. So what are you talking about?
>>
>>Well, Kevin's obsolete definition might have been better if he had said
>>*mass* instead of "*weight* of 27.7015 cubic inches...".
>
>
> But since the pound has historically been a unit of force, it is
> definitely better to speak of "weight".
Yeah, it is obvious that the pound is a unit of force, which is why
we need expressions like "pound force" or "lbf", which explicitly add
the qualifier "force" to make sure that the obvious is not overlooked.
>>One might speak of weightlessness, e.g. in orbit. It wouldn't occur to an
>>astronaut, however, to say that he/she's massless... Astronauts composed
>>of non-baryonic matter, and hence travelling at light speed, would be an
>>interesting concept, indeed...
>>
>>For those confused about these notions, the pound-force is the weight, or
>>*force* exerted by a pound of mass subjected to an acceleration of 1G; as
>>such, its expression in SI units would be in Newtons.
>>The pound, OTOH, is a unit of *mass*, and would be expressed in SI units
>>in Kilograms.
>
> According to every technical book I have ever used, the pound is a unit
> of force. Ergo, pounds measure weight. Kilograms measure mass. This
> is the reason that, in English (Sepponian) units, there is a no
> non-unity non-dimensionless constant called gc (g sub c), which relates
> force to mass. Here's a quick review for those of you having
> difficulty:
>
> http://gems.mines.edu/~mckinnon/DCGN209/Handouts/gc%20summary.pdf
The fact that you perceived "pound" only as a unit of force is *your*
problem. Didn't it occur to you at all that the term might have been
used to refer to mass, then? I guess this kind of confusion explains
a bit why Sepponians still mix up their units and lose e.g. the occasional
spacecraft doing so.
The fact that you quote a handout from some Sepponian college which has
no qualms calling the "gc" factor appearing in Newton's 2d law of motion
a "universal gravitational constant" also makes me wince. One wonders
what that lecturer would call the constant found, say, in the inverted
square law expressing the gravitational attraction between massive bodies...
Anyway, you seem to be still quite confused about your units and your
dimensional equations. The "32.2" gc conversion factor only derives from
the fact that 1G of acceleration happens to be, in the foot-pound-second
system, 32.2 ft/s**2. If pound expresses mass and lbf expresses a force,
then to what extent is gc's *dimensionality* in the foot-pound-second system
different from the SI system's?
It would also be interesting to know whether you consider the pound, as
a mass unit, to be a unit derived from the lbf, a bit like pressure,
say, is a unit ultimately derived from mass, length and time...
> Further evidence that the pound is a unit of force comes from
> established terms like "ft-lbs", which I hope everyone will agree is a
> unit of torque, not some mysterious unit of dimension (mass)x(length).
In English, "further" should be used when one has already presented a
modicum of evidence supporting an argument. Why should the fact that
it's more expedient in everyday language to talk about foot-pounds rather
than foot-pounds-force be any more significant than, say, Shakespeare
musing about a "pound of flesh" or your local grocer selling foodstuffs
by the pound?
> You might also want to check out what a "slug" is.
Webster's definition:
slug: the gravitational unit of mass in the foot-pound-second system
to which a pound force can impart an acceleration of one foot per
second per second and which is equal to the mass of an object
weighing 32 pounds.
Notice how Webster explicitly uses the term "pound force" -- despite
the fact that "force" should have been redundant, since according to
you, the "pound is a unit of force" ?
Furthermore, note that Webster speaks of "the *mass* of an object
weighing 32 *pounds*"? How dare they use terms like "pounds" when
talking about the mass of an object! Surely they need a refresher
course in English language usage!
>>>>3. your definition is /less/ accurate than using a standard object
>>>> (perhaps this would be an interesting homework project for you.
>>>> Discuss a practical way of maintaining as constant the 3 variables,
>>>> volume, temp, and atmospheric pressure. Be sure to mention the
>>>> effect of measurement on values)
>>>
>>>Umm, why couldn't you use any number of commercially available devices
>>>to maintain the desired temperature, volume, and pressure?
>>
>>First, because mass definitions involving a measurement of pressure
>>might be circular, as the standard pressure definition relies on mass,
>>acceleration and surface units... (Hint: how is the Pascal defined?)
>
> Yes, but the definition under discussion here was not a definition of
> mass. Ergo, no tautology.
No tautology only if we assume that pound is a unit of force, a point
with which I, um, forcefully disagree. Besides, one then wonders why
people have the strange idea of bringing up pounds in a thread discussing
mass and kilograms...
> Your points about accuracy are well-taken; I
> do understand that there were reasons that the weights and measures
> people adopted the Pt-Ir standard. But if 1893 levels of precision are
> what we're talking about, then the devices today would perform
> admirably.
Nope, in precision terms, today's devices are no better than 1893's, as
far as mass references are concerned. THIS IS WHY METALLIC REFERENCES
ARE STILL IN USE EVEN IN 2003, BY THE WAY.
>>Second, because there's no practical way to measure and regulate the
>>volume, temperature and pressure with the required precision.
>>The Pt+Ir mass references have an estimated error in the 10**-9 to
>>10**-8 range, which is the major reason these seemingly quaint objects
>>are still used, well, as mass references...
>
> If we updated the definition to be the weight of a certain volume of
> liquid water at its triple point, wouldn't that take care of the
> temperature and pressure problem? How hard is it to measure volume
> precisely?
I think if there was a precise way of determining that a sample of water
was uniformly at its triple point, as well as a way of determining its
volume, such that the measurement errors (temp, pressure etc) would have a
combined accuracy better than, say, 10**-9, we'd already have heard of it,
and metrologists all over the world would have discarded their metallic
mass references long ago...
How the calibrated masses of water would then be reproduced and shipped
to the standard institutes all over the world, while maintaining a 10**-8
or 10**-9 accuracy, would also be an interesting challenge. Weight
references, a bit like coordinated universal time references, have to be
statistically measured and adjusted against independent references to have
credibility...
>>There's no better mass reference system known as of yet, even though
>>some new ideas are being investigated -- e.g. the Avogadro crystal
>>lattice approach based on accurately estimating the number of Si
>>atoms in a "perfect" sphere, whose dimensions are controlled by
>>interferometry.
>
> What is the current uncertainty in Avogadro's number?
Avogadro number's relative uncertainty: about 8 * 10**-8
> Why can't the
> standard unit of mass be the nucleus of one atom of carbon-12, which
> already has an atomic mass of 12 amu by definition.
If we're talking about a large number (10**20+?) of C12 atoms, then to
obtain that bunch with an isotopic separation BETTER THAN 10**-8 or
10**-9 would be, I'm afraid, quite challenging. (Damn isotopes!)
If we're talking about using a small sample of isotopically pure reference
C12 atoms, I suspect that decorrelating e.g. the Van der Waals effects (a
factor with atomic force microscopes) with the measurable effects of the
mass proper (with a mass spectrometer?) at 10**-9 would be also, um, quite
"difficult".
I also suspect the engineering costs required to manipulate and count
single C12 atoms as weight references in a non-contaminating manner would
make the current prices of high-purity fullerene or carbon nanotube samples
appear, well, utterly laughable.
If you can devise a practical way of using single atoms as an accurate and
practical mass standard, I wouldn't be surprised if you'd get a phone call
from a committee in Stockholm... (I think there's a team working on it in
Sepponia, using the conductivity properties of Au aggregates)
Gene Nygaard
> Ken wrote:
> >
> > Curt Fischer wrote:
> > >
> > > Brett Robson wrote:
> > >
> > >>>The last I heard, the Avoirdupois pound was defined as being the weight of
> > >>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> > >>>being at 30 inches.
> > >>
> > >>1. avoirdupois pound is not an imperial pound
> > >
> > > You're right here. Congratulations. Don't let it go to your head
> > > though....
> > >
> > >>2. your definition is pound-force not pound
> > >
> > > A pound force is a pound. So what are you talking about?
> >
> > Well, Kevin's obsolete definition might have been better if he had said
> > *mass* instead of "*weight* of 27.7015 cubic inches...".
>
> But since the pound has historically been a unit of force,
Wrong. Pounds have always been units of mass. Pounds force are a
recent spinoff, something that was never well defined before the 20th
century, and which even today don't have an official definition.
Only one of the hundreds of pounds used throughout history has given
rise to a force unit of the same name--that's how recent the history
of the pound force is.
> it is
> definitely better to speak of "weight".
That's a big part of your problem, a failure to understand that
"weight" is an ambiguous word, one with more than one meaning. It is
a synonym for mass (in physics jargon) more often than it is a
particular kind of force in archery jargon for draw weight of a bow,
or a different kind of force (due to gravity) in physics jargon.
The troy units are units of weight--but they are always units of mass,
never units of force.
Weight means the very same thing as mass (in its physics jargon
meaning) whenever anyone talks about "net weight" or "troy weight" or
"carat weight" of a diamond or "dry weight" or "atomic weight" or
"molecular weight" and in many other instances.
>
> > One might speak of weightlessness, e.g. in orbit. It wouldn't occur to an
> > astronaut, however, to say that he/she's massless... Astronauts composed
> > of non-baryonic matter, and hence travelling at light speed, would be an
> > interesting concept, indeed...
> >
> > For those confused about these notions, the pound-force is the weight, or
> > *force* exerted by a pound of mass subjected to an acceleration of 1G; as
> > such, its expression in SI units would be in Newtons.
> > The pound, OTOH, is a unit of *mass*, and would be expressed in SI units
> > in Kilograms.
>
> According to every technical book I have ever used, the pound is a unit
> of force.
Pounds force exist. Many technical books use them (and so do people
in their everyday lives, usually as part of a unit of some other
quantity such as pressure), but many of those which do also use pounds
as units of mass. Furthermore, even the ones which don't use them as
units of mass usually mention pounds as units of mass; it is only in
the past couple of decades that you can run into a few textbook
authors so poorly educated that they don't understand that pounds are
units of mass.
>Ergo, pounds measure weight.
There's no "ergo" about it. Pounds often measure weight when they are
units of mass. Pounds force occasionally measure weight, but are most
often used for various types of force that are never called weight.
>Kilograms measure mass.
True, with two big caveats.
When they are units of mass, they are units of weight:
NPL (the U.K. national standards laboratory) FAQ
http://www.npl.co.uk/force/faqs/forcemassdiffs.html
Weight
In the trading of goods, weight is taken to mean the
same as mass, and is measured in kilograms. Scientifically
however, it is normal to state that the weight of a
body is the gravitational force acting on it and hence
it should be measured in newtons, and this force
depends on the local acceleration due to gravity.
To add to the confusion, a weight (or weightpiece)
is a calibrated mass normally made from a dense
metal, and weighing is generally defined as a
process for determining the mass of an object.
So, unfortunately, weight has three meanings
and care should always be taken to appreciate
which one is meant in a particular context.
NIST (the U.S. national standards laboratory) Special Publication 811
(1995 ed.), Guide for the Use of the International System of Units
(SI):
http://physics.nist.gov/Pubs/SP811/sec08.html
In commercial and everyday use, and especially in common
parlance, weight is usually used as a synonym for mass.
Thus the SI unit of the quantity weight used in this
sense is the kilogram (kg) and the verb "to weigh" means
"to determine the mass of" or "to have a mass of".
Examples: the child's weight is 23 kg
the briefcase weighs 6 kg
Net wt. 227 g
Second caveat: kilograms force also exist, and used to be quite
acceptable. They were officially endorsed by the CGPM in 1901 when
they adopted a "standard acceleration of gravity" for the purpose of
defining grams force, and were acceptable until the adoption of the
International System of Units (which doesn't include kilograms force)
in 1960.
We still see many vestiges of the use of this once-acceptable unit
today: pressure gauges in kg/cm², torque wrenches in
"meter-kilograms" (the SI unit is newton-meters) are still readily
available, and thrust of rockets or jet engines (as they were most of
the time in the Russian space program into the late 1980s or early
1990s, or in Tom Clancy's nonfiction work _Airborne_, 1997).
>This
> is the reason that, in English (Sepponian) units, there is a no
> non-unity non-dimensionless constant called gc (g sub c), which relates
> force to mass.
So, in this dreamworld of yours, what exactly is the standard for that
pound? What is its nature--something electrical, mechanical, or what?
Exactly when (to the year is good enough, or a range of years if you
cannot do any better) was it made a standard, and by whom? To whom
does that standard apply? Who maintains this standard, and where is
it kept?
>Here's a quick review for those of you having
> difficulty:
>
> http://gems.mines.edu/~mckinnon/DCGN209/Handouts/gc%20summary.pdf
>
> Further evidence that the pound is a unit of force comes from
> established terms like "ft-lbs", which I hope everyone will agree is a
> unit of torque, not some mysterious unit of dimension (mass)x(length).
Yes, it is ft·lbf for energy or work, and either ft·lbf or lbf·ft for
torque. In earlier times, and in places outside North America,
foot-poundals were more common for these purposes than they are not.
American Society for Testing and Materials, Standard for Metric
Practice, E 380-79, ASTM 1979.
3.4.1.4 The use of the same name for units of force
and mass causes confusion. When the non-SI units
are used, a distinction should be made between force
and mass, for example, lbf to denote force in
gravimetric engineering units and lb for mass.
Of course, symbols for units of measure should also remain unchanged
in the plural--no language-specific "s" at the end, for example.
Now, you define for us a British thermal unit. How much water?
That's not the water which exerts a certain amount of force, is it?
What does it mean if a physicist says the latent heat of fusion of
water is 80 Btu/lb? Or measures specific heat capacity in
Btu/(lb·°F)? What are those units in the denominators?
>
> You might also want to check out what a "slug" is.
Tit for tat. You ought to check out what a poundal is.
This is the English unit of force in a system which is much older than
the one which contains slugs.
Slugs are a little used 20th century invention, which didn't appear in
engineering textbooks before 1920 or in physics textbooks before 1940.
They exist only in one specific system (out of several such systems)
of mechanical. After a brief heyday, mostly in the U.S. and Canada
(they weren't ever used much in any other places using English units),
they have pretty much disappeared again.
The system of mechanical units in which slugs exist is, like SI, a
"coherent" system of units, as that term is used in metrology jargon.
That means that in the only system which has slugs, there are no pints
or gallons of any kind, not U.S. liquid nor U.S. dry nor imperial.
There are no horsepower, no Btu, not even any psi because there are no
inches or miles or ounces. These specialized systems of mechanical
units are only used only in calculations, and you often have to
convert into those systems before you can use them, or out of them at
the end because the units you want to use aren't in that system, or
both.
Poundals are the derived units of force in a different coherent
foot-pound-second system of mechanical units. They are the force
which will accelerate the base unit of mass in this system at a rate
of 1 ft/s².
Fill in the blank: the base unit of mass in this oldest fps system of
English mechanical units is the _____________. (Hint: it is the "p"
in this fps system.)
>
> >
> > >>3. your definition is /less/ accurate than using a standard object
> > >> (perhaps this would be an interesting homework project for you.
> > >> Discuss a practical way of maintaining as constant the 3 variables,
> > >> volume, temp, and atmospheric pressure. Be sure to mention the
> > >> effect of measurement on values)
> > >
> > > Umm, why couldn't you use any number of commercially available devices
> > > to maintain the desired temperature, volume, and pressure?
> >
> > First, because mass definitions involving a measurement of pressure
> > might be circular, as the standard pressure definition relies on mass,
> > acceleration and surface units... (Hint: how is the Pascal defined?)
>
> Yes, but the definition under discussion here was not a definition of
> mass. Ergo, no tautology.
Wrong. It was a definition of mass--you are just too dumb to
understand one of the words used in that definition.
>Your points about accuracy are well-taken; I
> do understand that there were reasons that the weights and measures
> people adopted the Pt-Ir standard. But if 1893 levels of precision are
> what we're talking about, then the devices today would perform
> admirably.
You cannot measure force today to anywhere near the accuracy which the
weights and measures experts could measure mass in 1893.
> Oh, I see, wait...Brent may have misinterpreted as serious Kevin's
> suggestion that we return to English units!
>
> > Second, because there's no practical way to measure and regulate the
> > volume, temperature and pressure with the required precision.
> > The Pt+Ir mass references have an estimated error in the 10**-9 to
> > 10**-8 range, which is the major reason these seemingly quaint objects
> > are still used, well, as mass references...
>
> If we updated the definition to be the weight of a certain volume of
> liquid water at its triple point, wouldn't that take care of the
> temperature and pressure problem? How hard is it to measure volume
> precisely?
How easy is it to maintain a whole pound of water at exactly that
triple point, all the way to the edge of the container?
A lot harder than it is to measure mass precisely.
>
> > There's no better mass reference system known as of yet, even though
> > some new ideas are being investigated -- e.g. the Avogadro crystal
> > lattice approach based on accurately estimating the number of Si
> > atoms in a "perfect" sphere, whose dimensions are controlled by
> > interferometry.
>
> What is the current uncertainty in Avogadro's number? Why can't the
> standard unit of mass be the nucleus of one atom of carbon-12, which
> already has an atomic mass of 12 amu by definition.
Because your eyesight isn't good enough to count the number of those
atoms I use to balance a kilogram of hamburger--even if you had the
time and the ability to do the actual counting.
--
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
"It's not the things you don't know
what gets you into trouble.
"It's the things you do know
that just ain't so."
Will Rogers
Michael Cash
<nih...@paxonet.kom> belched the alphabet and kept on going with:
>Ken wrote:
>
>
>> *Any* decent high-school physics text should have made clear the
>> fundamental difference between weight -- e.g. pound-force -- and mass
>> -- e.g. pound -- units... Whether the difference will be understood
>> by all the students is another matter, of course.
>
>What the hell ever happened to slugs?
I spilled salt on them. Sorry for the inconvenience.
Curt Fischer
> today: pressure gauges in kg/cmイ, torque wrenches in
> "meter-kilograms" (the SI unit is newton-meters) are still readily
> available, and thrust of rockets or jet engines (as they were most of
> the time in the Russian space program into the late 1980s or early
> 1990s, or in Tom Clancy's nonfiction work _Airborne_, 1997).
>
> >This
> > is the reason that, in English (Sepponian) units, there is a no
> > non-unity non-dimensionless constant called gc (g sub c), which relates
> > force to mass.
>
> So, in this dreamworld of yours, what exactly is the standard for that
> pound? What is its nature--something electrical, mechanical, or what?
> Exactly when (to the year is good enough, or a range of years if you
> cannot do any better) was it made a standard, and by whom? To whom
> does that standard apply? Who maintains this standard, and where is
> it kept?
>
> >Here's a quick review for those of you having
> > difficulty:
> >
> > http://gems.mines.edu/~mckinnon/DCGN209/Handouts/gc%20summary.pdf
> >
> > Further evidence that the pound is a unit of force comes from
> > established terms like "ft-lbs", which I hope everyone will agree is a
> > unit of torque, not some mysterious unit of dimension (mass)x(length).
>
> Yes, it is ftキlbf for energy or work, and either ftキlbf or lbfキft for
> torque. In earlier times, and in places outside North America,
> foot-poundals were more common for these purposes than they are not.
>
> American Society for Testing and Materials, Standard for Metric
> Practice, E 380-79, ASTM 1979.
>
> 3.4.1.4 The use of the same name for units of force
> and mass causes confusion. When the non-SI units
> are used, a distinction should be made between force
> and mass, for example, lbf to denote force in
> gravimetric engineering units and lb for mass.
>
> Of course, symbols for units of measure should also remain unchanged
> in the plural--no language-specific "s" at the end, for example.
>
> Now, you define for us a British thermal unit. How much water?
> That's not the water which exerts a certain amount of force, is it?
>
> What does it mean if a physicist says the latent heat of fusion of
> water is 80 Btu/lb? Or measures specific heat capacity in
> Btu/(lb薫F)? What are those units in the denominators?
>
> >
> > You might also want to check out what a "slug" is.
>
> Tit for tat. You ought to check out what a poundal is.
>
> This is the English unit of force in a system which is much older than
> the one which contains slugs.
>
> Slugs are a little used 20th century invention, which didn't appear in
> engineering textbooks before 1920 or in physics textbooks before 1940.
> They exist only in one specific system (out of several such systems)
> of mechanical. After a brief heyday, mostly in the U.S. and Canada
> (they weren't ever used much in any other places using English units),
> they have pretty much disappeared again.
>
> The system of mechanical units in which slugs exist is, like SI, a
> "coherent" system of units, as that term is used in metrology jargon.
> That means that in the only system which has slugs, there are no pints
> or gallons of any kind, not U.S. liquid nor U.S. dry nor imperial.
> There are no horsepower, no Btu, not even any psi because there are no
> inches or miles or ounces. These specialized systems of mechanical
> units are only used only in calculations, and you often have to
> convert into those systems before you can use them, or out of them at
> the end because the units you want to use aren't in that system, or
> both.
>
> Poundals are the derived units of force in a different coherent
> foot-pound-second system of mechanical units. They are the force
> which will accelerate the base unit of mass in this system at a rate
> of 1 ft/sイ.
Thanks for your exhaustive response. It appears that I have been
systematically miseducated by a number of professors and widely used
textbooks throughout my career as a Sepponian engineering student.
Sorry for anything incorrect I may have said.
Secondly, Google reveals that you have dedicated a large portion of your
usenet presence to proselytize these facts to the multitudes. Why such
tenacity?
--
Curt Fischer
Kevin Gowen
Whoa. It seems like his passion for weights and measures has grown so much
that he scours usenet for discussions of them while pretending to work.
I never thought that this would be such a successful troll.
--
Kevin Gowen
Gene Nygaard
wrote:
>
>Thanks for your exhaustive response. It appears that I have been
>systematically miseducated by a number of professors and widely used
>textbooks throughout my career as a Sepponian engineering student.
>Sorry for anything incorrect I may have said.
>
>Secondly, Google reveals that you have dedicated a large portion of your
>usenet presence to proselytize these facts to the multitudes. Why such
>tenacity?
Because this miseducation is a widespread, institutional problem--one
that keeps cropping up all over the place.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/