I think that NIST has a reasonable view of things, not surprisingly
since they serve both technical and public communities. In section 8.3,
NIST SP 811 provides a technical definition of weight (as a force) and
then states
[quote]
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.”
[end quote] http://physics.nist.gov/Pubs/SP811/sec08.html
So, NIST recognizes that public usage is not technically correct and yet
NIST seems to have no problem with it. Nor do I. We have no verb "to
mass" (except as might be used by priests in Roman Catholic and other
liturgical denominations) in the English language.
I'm too busy trying to teach people to use the metric system to be
bothered with undertaking a revision of our national language and
speaking practices.
Yes, I can find the weight (mass) of an egg layed by one of my hens
using an equal arm balance, a spring scale, or an electronic balance
utilizing calibrated load cells. I prefer the latter device and that's
the one I use to weigh my eggs.
Now, in talking with people, I most likely will tell them that this
particular egg has a mass of 68 g and that I weighed it myself. I use
"mass" for the noun because I have a science and engineering background
and am comfortable with that. If some of the brighter folks, or folks
who have heard the distinction before in some course of study, pick up
on that and continue that practice, I'm delighted. If others wish to
remain casual in their speech or don't know the distinction and wish to
use "weight" as the noun, I'm quite willing to let that go uncorrected.
What I care about is that they grasp "68 g". Literally, if needed. For
example, if they ask "How much is 68 g?", expecting some sort of answer
in ounces I suppose, I hand them the egg to hold in their own hand and I
say "That much." If they persist and ask how many ounces that is, I tell
them I don't know -- and that's the truth.
My normal goal is to teach folks in our community to use the SI, not to
teach them legal metrology. When I do technical consulting, the rules
change and I do teach the distinction between mass and weight.
Let's get them into the church, for now. Later, maybe we can train some
of those who stick around to become theologians.
Jim
[email protected] wrote:
Jim,
My definition of "weighing" (or to weigh) is "the precess of balancing forces
(newtons), usually for the purpose of measuring the mass (grams or kilograms) of an object."
A spring balance (of forces) may be used. The spring must be calibrated for
its particular location if it is to display units of mass accurately.
An equal-arm (or even an unequal-arm) balance of forces may be used for a more direct
measurement of mass by comparison with "standard masses" on one side of the
balance.
My position is that the term "weighing" (or to weigh) for the purpose of
measuring mass is fully compatible with SI. The results, if displayed in grams or
kilograms, should be called *mass*.
Grams and kilograms should not be called weight if usage is to be compatible
with declarations of the CGPM and NIST.
Do you accept each the statements above for teaching SI?
Which, if any, do you contend is "more pure SI" than declarations of the CGPM
or NIST, and not appropriate for teaching SI?
As a retiree, I have the time to engage in these exchanges if for nothing more
than maintaining a level of brain activity.
Gene.
---- Original message ----
Date: Mon, 26 Jan 2009 20:01:24 -0600
From: James Frysinger <[email protected]>
Subject: [USMA:42613] Re: The real physics (was Small item seen on TV)
To: "U.S. Metric Association" <[email protected]>
It's amazing how we can get wound up on some hot topics around here. (My
personal sore spot tends to be on getting the laws of physics right.)
I have no qualms about you telling your doctor that you weigh 104 kg.
You have NIST SP 811 on your side regarding the use of "weigh' as a verb.
Of course, some folks here have a vision of SI that is much more pure
than NIST's or even CGPM/CIPM's.
Jim
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
