RV-7a baggage area

Fred the Red Shirt wrote:

Russell Kent wrote in message ...


I'm sorry, you're correct. I didn't mean to imply that they are the only unit of
mass. I was taught (perhaps incorrectly) that the unambiguous term for weight
(scientific meaning) in the English system was "slugs". Apparently it's also
"pounds force" now (it may have been them, too, and I've just forgotten it).

I think you mistyped. 'Slugs' are unambiguously a unit of mass.

Oy. You are correct, sir.

Pounds are ambiguously a unit of force. Ambiguity exists because it
is popular in some disciplines to use a unit of mass defined (loosely)
as that mass which weighs one pound.

But you knew that.

Ibid. :-)

Russell Kent

On Mon, 08 Dec 2003 15:43:53 -0600, Russell Kent
wrote:

Gene Nygaard wrote:

I see that even that wasn't enough to get your attention, Chicolini.

OK, you got me there. Haven't a clue who Chicolini is. Should I be insulted? Do
you now feel better having insulted me?

Doesn't cost you any more to pay attention. It's from the Groucho
Marx quote.

How big a bat do I need to hit you over the head with to get your
attention?

Clear, intelligent statements usually work.

I know better from long experience. If I hadn't clubbed you over the
head, you still wouldn't have looked into it enough to learn the
significant amount you have already learned, to be singing a
different tune now.

Still wrong, of course, but a totally different tune nonetheless.

Besides gently (IMHO)
chastising the intervening poster's rant, I still provided a useful answer to
the original poster's question (12+ cu. ft.) and a reference to the source.

Yes, you got that right. Too bad nobody will pat you on the back for
it,

(I don't care)

because you obscured it with irrelevant nonsense,

Irrelevant? Wasn't to me. Nonsense? Um, nope.

and even worse, an incorrect claim of error on someone else's part.

Perhaps.

Uh, 2 years of high school physics (a jillion years ago). Perhaps a few web
references will help clear the cobwebs:

If you found those references, you also found many that got it right.

I just grabbed a few that looked to get to the point quickly.

http://scienceworld.wolfram.com/physics/Slug.html

Slugs are units of mass. That's not what I'm calling you on.

It wasn't clear in your earlier hostile response.

But that little-used 20th century invention, which didn't even appear
in physics textbooks before 1940, are by no stretch of the imagination
_the_ units of mass in "the English system."

I'm sorry, you're correct. I didn't mean to imply that they are the only unit of
mass. I was taught (perhaps incorrectly) that the unambiguous term for weight
(scientific meaning) in the English system was "slugs".

Must have been an overload of new learning, making you mistakenly
express what you thought you knew before.

Apparently it's also
"pounds force" now (it may have been them, too, and I've just forgotten it).

Pounds force also exist, but that's also beside the point.

sarcasm Whew. Glad we're past that. /sarcasm

Back up your claim that pounds are not units of mass. That's where you falsely
claimed that Dave S. was making an error.

Actually, I intended only to claim that Dave S. incorrectly stated mass when he
should have stated weight.

Dave S. said mass.

Dave S. meant mass.

Dave S. was absolutely correct.

Sure, he could also have said weight. But that wouldn't have been
clear and unambiguous as what he said was ("mass," of course, is also
ambiguous, with several different meanings--but unlike the situation
with "weight," only one of the meanings of "mass" is used with a
number to express its magnitude). Had he said "weight" instead of
"mass," you and many others would likely have misinterpreted it as
having something to do with the strength of the local gravitational
field.

From my perspective, the respondent about whom Dave S.
was complaining clearly intended "lbs" as a unit of weight.

So what? Weight is an ambiguous word, one with several different
meanings. Dave S. made clear which one he meant--and he was right.

Yes, those pounds are units of weight. But let's look at the other
pounds still in use today.

First, consider the troy units of weight. That phrase doesn't set off
any alarms with you, I'd bet, nor with anyone else. The troy pounds,
of course, aren't used much any more (and were outlawed in Great
Britain back in the 19th century). But the troy ounces are still in
general use, even enjoying a special exception from the metrication
laws of places such as Australia and the United Kingdom.

But there is one very interesting thing about those troy units of
weight--unlike their avoirdupois cousins, and unlike grams and
kilograms, they have never spawned a unit of force of the same name.
These units of weight remain always units of mass. There is no troy
ounce force and there never has been one.

The other pounds still in use today in various places of Europe and
Latin America are the redefined metric pounds, which replaced many
other old pounds back in the 19th century. They are 500 grams, or
half a kilogram, exactly--units of mass.

I'm sure that you are aware that not everybody uses pounds to measure
this "baggage weight." In fact, most of the people of the world use a
different unit. Don't suppose you could figure out what that might
be, could you? Tell us what those units are. Here's some help:
http://www.google.com/search?hl=en&i...=Google+Search

Those kilograms are the proper SI units for this baggage weight.

Nobody uses newtons for this weight. Nobody uses poundals for this
weight. Nobody uses kilograms force or pounds force for this weight.
Nor should they.

The reference to the slug as the English mass unit was only intended as an offhand
remark. Pounds are units of mass in casual (non-technical) conversations, and
probably shorthand for "pounds force" in technical conversations.

We don't have separate standards for technical use and for
non-technical use. Either way, a pound is 0.45359237 kg. A pound
force (also, as you point out, often not distinguished from other
pounds) doesn't actually have an official definition, at least in the
United States, but it is 4.448 N and change in any of the definitions
used.

Do I need to go into things like specific impulse, where American
engineers often get this quantity in units of "seconds"? There is, of
course, also an SI unit called a second--but the SI units of specific
impulse are newton seconds per kilogram, or the equivalent meters per
second. Those American engineers only got these pseudo-seconds in the
first place by being sloppy and calling both a unit of force and a
unit of mass by the same name--pound--and then canceling one out with
the other.

Do I need to go into what it means when NASA tells us that the Apollo
11 Lunar Module had a liftoff weight of 10,776.6 lb? Or hundreds of
other similar measurements at various stages of all the Apollo
missions? Selected Mission Weights
http://history.nasa.gov/SP-4029/Apol...on_Weights.htm

Do I need to go into things like British thermal units, and specific
heat in Btu/(lb °F)?

Do I need to get into poundals? There's another unit, which like the
slug is only used in a technical context, only to simplify
calculations by making it easier to keep track of the units in the
result of those calculations.


For the record, I don't claim that slugs are the only unit of mass in the English
system, and I'm sorry to have inadvertantly made that implication.

Russell Kent

Just to make it clear to others who might not pick up on this as
quickly as you did, I'll point out that the most common English units
of mass are pounds, ounces (avoirdupois or troy), and tons (long or
short). Also bushels, as they are used in the commodity markets and
grain elevators today--as a specified amount of mass, different for
various commodities.

Now let's pick up a couple more points from your earlier followup to
your own message as well:

On Mon, 08 Dec 2003 15:19:03 -0600, Russell Kent
wrote:

OK, I know it's bad form to follow-up one's own posting. So sue me. :-)

Gene,
I see from your signature that this "weight vs. mass" thing is a personal windmill
for you. Fine. And I see that slug isn't used anymore (pound-force is the term
now).

Pounds force and slugs are different things. One is a unit of force,
the other a unit of mass. Maybe you are getting mixed up with
poundals, which are units of force in a completely different
different, much older fps system of units. Guess what the units of
mass are in that oldest English system of mechanical units.

And for non-technical conversations, pound is a unit of mass.

Baggage weight is a measurement of mass, in either a technical or
nontechnical context. Talking about the sale of cheese in a physics
class doesn't change the rules governing its sale. See "Physicist qua
Cheesemonger (U. of Winnipeg)"
http://groups.google.com/groups?safe...nger&lr=&hl=en

Pounds are used both as units of mass and as units of force in
technical contexts. Sensible people follow the rules and identify the
recent spinoff as "pounds force": 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.

Here's a question though: is this forum a technical or non-technical conversation?

That would be one of the least reliable clues to the meaning of any
words used here.

And look at the sequence of postings: EUTNET wrote that the baggage area dimension
was 100 lbs, obviously meaning *weight*, and Dave S. complained that EUTNET
"cannot tell the difference between MASS and VOLUME." [emphasis Dave's] So I
believe Dave should have instead written "WEIGHT and VOLUME."

You believe wrong.

Now I suspect that Dave S. was merely careless and really does understand the
difference between mass and weight, and I was trying to gently pass along the
advice that newsgroup corrections are invariably inspected for even the slightest
error (see this thread!). I welcome you (Gene) jumping in at that point to
correct the whole weight vs. mass, slugs, pound-force hullabalu, but I wish you'd
do it with a bit less hostility. Someone may well have ****ed in your cornflakes,
but I assure you it wasn't me. :-)

Russell Kent

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