He is right. Gravity is not constant from one location to the next. For
example if we look a W. 105 and move to W. 15 we have moved from a gravity
hole to a gravity peak.The core of the Earth is like spinning a egg, in our
case the core has not come up to the speed of the surface and locations of
higher mass move but give us the 2 valley 2 peak problem in mass/gravity. It
is very much to note if You are doing station keeping on a geo-syn sat. .

"Gene Nygaard" wrote in message
...
On 11 Dec 2003 09:52:27 -0800, (Fred the Red
Shirt) wrote:

Gene Nygaard wrote in message
. ..
On 10 Dec 2003 06:50:50 -0800, (Fred the Red
Shirt) wrote:



I was merely pointing out that you have it ass-backwards. There is
absolutely no looseness in the use of pounds as units of mass.

Non-sequitor. Loosness was never at issue. At issue was ambiguity.
Pounds can be either a unit of mass or a unit of force and often that
is not even made clear by the context. That pretty well fits the
defintion of ambiguous, does it not?

Slugs, OTOH, are only defined as units of mass. No ambiguity there.

The OP referred to slugs as ambiguous. The OP had it bass akwards.

--

FF



It is pounds force that are the recent spinoff, not the other way
around. It is pounds mass that are the venerable units, and pounds
force which are the *******ization, not the other way around.

I missed this part last time--I saw your signature above in the bottom
of the window, and assumed that the above was all you had written, and
didn't scroll down to see the rest and didn't see it when I replied
either.


Was not the pound ever defined as a unit of weight?

Certainly. But that doesn't mean "not mass."

Look at the millions of items in the grocery stores and in the
pantries of our homes today that list the "net weight" of our foods
and various other hardware and automotive products. The pounds on
them are every bit as much units of mass as the grams which appear
right alongside them.

Like I pointed out to Russell a long time ago in this thread, the troy
system of weights also includes pounds and ounces. But unlike their
avoirdupois cousins, and unlike grams and kilograms, the troy units of
weight are always units of mass. They have never spawned units of
force of the same name.

What's really strange is that there are always some fools who will
insist that when we buy and sell goods by weight, we'd want to measure
some quantity that varies with location. How stupid can some people
be?

Get it through your thick skull that "weight" is an ambiguous word,
one with several different meanings. Note also that "net weight" is
not a physics term. If you are talking about a "weight" which is the
force due to gravity, then you can't ignore the container, unless
you've invented something that is invisible to gravity. Whenever
anybody talks about "net weight," that weight is the very same thing
as what physicists often call "mass" in their jargon.

If it was
defined as a unit of weight then it was simultaneously defined as
a unit of force without regard to whether or not the person(s)
defining it UNDERSTOOD that they were doing so.

Bull****.

The meaning of "weight" which is a synonym for "mass" in physics
jargon is quite proper and legitimate, well justified in history and
in linguistics and in the law.

It is, in fact the original meaning of the word weight, which entered
Old English over 1000 years ago meaning the quantity measured with a
balance. That quantity is, of course, mass--not force due to gravity.

Those balances were, of course, the only weighing devices anybody had
ever used even 200 years ago, and people had been weighing things for
something like 7000 years or more before then.

What you need to do is to take a look at how the standards for a pound
were propogated throughout the world. If someone made a copy of the
standard maintained at London, and took it to South Africa or to
Washington, D.C. or whereever, what exactly is it that is the same
about the pound in the new location? It exerts a different amount of
force in the new location, but it is still the same mass.

Maybe you should take a look at what the experts in the field have to
say about it, people such as the keepers of our standards. For
example, the national standards laboratories of the United Kingdom and
of the United States:

Here's a FAQ by the NPL, the national standards laboratory of the
U.K.:
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.


Note--they clearly refer to different *meanings* of this word.

Here's NIST, the U.S. national standards agency, in their Guide for
the Use of the International System of Units, NIST Special Publication
811,
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

Note especially that last one--this is the proper usage for the sale
of chicken.

The National Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric
Practice Guide, January 1989:

5.7.3 Considerable confusion exists in the use of the
term "weight." In commercial and everyday use, the
term "weight" nearly always means mass. In science
and technology, "weight" has primarily meant a force
due to gravity. In scientific and technical work, the
term "weight" should be replaced by the term "mass"
or "force," depending on the application.

5.7.4 The use of the verb "to weigh" meaning "to
determine the mass of," e.g., "I weighed this object
and determined its mass to be 5 kg," is correct.

The thing to note here is the different treatment of the noun forms
and the verb forms, Contrast the application dependent meanings of
the former with the unqualified "is correct" in the latter.

The other thing to note is that "nearly always" is much stronger than
"primarily"--they even got that part correct.

Like the experts tell you, you are best off avoiding the word "weight"
in a technical context, and if you do use it, you need to make clear
which meaning is intended.

E.g. in your researches, what is the earliest definion of pound that
you can find?

Long before there was an England.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/