On Mon, 29 Sep 2003 10:12:33 -0700, Jim Kelley
wrote:
Gene Nygaard wrote:
My 'weight' is 230 pounds on earth. That's a fact.
My 'weight' would be 230 pounds on the earth's moon. That's also a
fact.
Your weight is defined as what you weigh on Earth, assuming a
gravitational acceleration of g. Obviously it's not true that your
weight would be measured as 230 pounds on the moon. The CRC Handbook of
Chemistry and Physics states that the weight of a body varies with
location, and defines weight as W = mg, where g is the local
acceleration due to gravity.
It doesn't cost you any more to pay attention.
Repeat to yourself until you understand it: Weight is an AMBIGUOUS
word. IT HAS SEVERAL DIFFERENT MEANINGS.
The one you cite from the Chemical Rubber Company is, of course, one
of those several definitions. If it always meant the same as mass in
physics jargon, I wouldn't have to point out to you that this is an
ambiguous word, would I?
Didn't you read the message you responded to, especially what
immediately followed the sentence you quoted? Didn't you see what
NIST and ASTM have to say about this? Look at it again, and read it
slowly this time
Let's review what I've already posted in other messages in this
thread, from ASTM
. . . thus, when one speaks of a person's weight,
the quantity referred to is mass. . .
and from NIST
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
Learn to evaluate your sources, also. Those sources are more credible
than any CRC Handbook on this subject.
Your definition of weight is not the proper one to use for your body
weight in the doctor's office or the gym. It is not the one used in
our hospitals. It is not the one used in weighing an NFL lineman at
380 lb, which is equal to 0.98 slinches in one system or 11.8 slugs in
another system of those strange units only used in calculations, only
in the sciences, and only in North America to any significant extent
(people in other English-units countries continued to use the absolute
fps system with force in poundals until they converted to the metric
system in their engineering).
You can, of course, choose not to call this quantity "weight." You
can call it mass instead, if you want to.
But keep in mind that if you do make that voluntary decision, that
fact doesn't prove that anyone else is making an error if they call it
"weight."
Furthermore, it is not an acceptable option to misinterpret what they
are saying, and to misapply an inappropriate definition of weight.
You could, of course, argue that we should all change to your usage.
But you certainly aren't going to exert the effort that would be
necessary get us to give up a word to which we have a prior claim, if
you aren't smart enough to figure out that it would be a change.
Furthermore, to have any hope of success, you'd have to offer us a
verb as well as a noun.
Reflecting the apparent dichotomy, the CRC defines the pound both ways:
"1. A unit of mass equal in the U.S. to 0.45359237 kg. exactly.
2. Specifically, a unit of measurement of the thrust or force of a
reaction engine representing the weight the engine can move, as an
engine with 100,000 pounds of thrust. 3. The force exerted on a one
pound mass by the standard acceleration of gravity."
That really shouldn't come as any surprise to you, does it, at this
stage of the game?
Interestingly, they also define poundal, pound mass and pound weight.
No mention of pound force. Evidently, that would be redundant. ;-)
Have you figured out yet what those poundals are, and how they are
used? What is the base unit of mass in the system in which these
force units are used?
One thing about the CRC Handbook (which edition?) is that they include
stuff put in there over a period of many years, most of it undated.
Those "pounds weight" are an obsolete term for what are now called
pounds force.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/