On Thu, 25 Sep 2003 20:06:37 GMT, Dave Shrader
wrote:

You are equating pound and POUNDAL ['pound mass']. They are two
different things.

Good grief! Go find a dictionary, or a physics book published before
1940 (and a number of them published later as well, it's just that for
the 60 years before then it's a virtual certaintly that you'll see
poundals used in these textbooks).

Poundals are unit of force. Not units of mass. A poundal is not a
pound mass; it is not mass at all. A poundal is also not a pound
force. In fact, it takes 32.16 pdl or 32.1740... pdl or 32.175 pdl,
or something in that neighborhood, to make a pound force. The exact
number will depend on how you choose to define a pound force, which
doesn't even have an official definition. The de facto standard today
is to define it so that it has the same relationship to a pound as a
kilogram force has to a kilogram. Or, that a pound force has the same
relationship to a kilogram force as a pound has to a kilogram.
That's what I'll use for any other related numbers below.

----------------------------------------

Sears and Zemansky, 1956, Table 5-1, page 77

Systems of units Force Mass Acceleration
Engineering pound Slug ft/sec^2
mks newton kilogram m/sec^2
cgs dyne gram cm/sec^2
----------------------------------------

Still too ****ing dumb to see any adjective there, identifying a
particular subset of English units? Even after it has been
specifically pointed out to you?

You know, I was tempted to give you the benefit of the doubt, and
assume that this had been sent before you had a chance to read my
discussion of the 1970 edition of Sears and Zemansky. But then I
double checked, not only that it graphically appeared to below that
message on my newsreader, but also that your message did indeed in
References the message ID of that one in which I discussed the 1970
ecition.

"One standard pound, by definition, is a body of mass 0.4535924277 kg."

I told you the number would be different, didn't I--but that S&Z would
not lie to you about the fact that pounds are units of mass.

"Since the weight of a body is a force, it must be expressed in units of
force. Thus in the engineering system weight is expressed in POUNDS; in
the mks system, in Newtons; and in the cgs system, in dynes."

Do you see any adjective modifying "system" here, in each of the three
times it is used?

Does the existence of a kilogram force prove that kilograms are not
units of mass? No. Does the existence of a pound force prove that
pounds are not units of mass? No.

Do you know that what they call the "engineering" system is, like SI,
a coherent system of units, as that term is used in the jargon of
metrology? Do you know what that means? It means that there is only
one unit for each different quantity, and that that unit is a unitary
combination of the base units.

Do you know the implications of that? That means that this system
which they identify as the "engineering system" doesn't have any pints
or gallons, no Btu or horsepower, no ounces or inches or miles or
furlongs or fortnights. That's the only system that includes
slugs--the one that doesn't have a whole lot of our commonly used
units.

What's more, that's only one of several such systems. Some of the
others include the absolute fps system (the one with pounds for mass
and poundals for force), the gravitational inch-pound-second system
(no slugs here either; the unit of mass in this system, equal to 1
lbf·s²/in, or about the weight (a synonym for mass in this case, of
course) of the heaviest NFL linemen today, is probably most often used
without a name, though some NASA engineers have called it a "slinch").

Unless you disagree with Newton's Second Law, F=ma, Force [pounds] and
mass [slugs] are related by acceleration [of gravity, for example].

You can just as easily say that force [poundals] and mass [pounds] are
related by the acceleration [ft/s²]. It's every bit as true--and that
system has been around a lot longer than the one with slugs.

Furthermore, Newton didn't use symbol to express this, and he only
said that force is proportional to mass times the acceleration of
gravity. Symbolically, that's F = kma. Using this more general form,
you can use any units you want to for each of these quantities, as
long as you make the constant k fit with them. That's what must be
done in the system generally called the English "engineering" system
of units (Sears and Zemansky are idiots who aren't even able to
understand the distinction between the system identified by this term
in normal usage by most other people, and the one they call by this
name which everyone else calls the "gravitational" or "gravimetric"
fps system of units). In what everyone else calls the engineering
system of units, pounds are used for mass and pounds force for force,
and for Newton's Second Law we have F = kma where k = 0.03108095 =
1/32.1740.

So, my weight [240 pounds] = my mass [7.45 slugs]*[gravity of 32.2
ft/sec^2].
-----------------------------------------
If you want to argue, go ahead. I cited a source as you asked. Now you
choose to disagree with that source.

Go read my quotes from NIST and from ASTM on the subject of human body
weight in my longest reply to Richard Clark.

My final comment: Does a newton[force] = a kilogram[mass]??

No. The numbers won't even be the same, unless you happen to be some
place outside this world where the local acceleration of free fall is
pretty close to 1 m/s².

Furthermore, a kilogram force doesn't equal a kilogram either, not
even if you call it by its other name, the kilopond. They measure
different quantities. On earth, the numbers associated with each
might be close to each other if the force you are measuring is the
force due to gravity--but that doesn't make them "equal."

Now here's something else for you to chew on. Just to show that there
have been people using metric units who have been bound and determined
to show that they can be every bit as silly as those using English
units, look up a unit of mass known variously as the hyl, or by the
German acronym TME, or as the mug, which is derived from another of
its names, the "metric slug." This is the mass which a kilogram of
force will accelerate at a rate of 1 m/s².

In that system, the base units are the meter for length, the second
for time, and the kilogram for force, with the hyl as the coherent,
derived unit of mass.

Note that in that system, kilograms are never units of mass. Exactly
the same as that system which Sears and Zemansky mislabel the
"engineering" system, a similar limited subset of the English units
rather than of the metric units, in which subset the pound is not used
as a unit of mass.

Granted, that system probably never did see extensive use, and I
haven't seen it used at all recently. But it's mere existence shoots
all kinds of holes in your theories related to Newton's second law,
and all the different names that the mass unit in this system has been
given are clear evidence that it has been independently reinvented
many times over.

The existence of the hyl does not prove that kilograms are not units
of mass. The existence of the slug does not prove that pounds are not
units of mass.

--------------

Conclusion:

Force = pounds, or newtons, or dynes.
Mass = Slug, or kilogram, or gram
Acceleration = ft/sec^2, or m/sec^2, or cm/sec^2
----------------------------------------
Don't be so everbearing! It does not become you or enhance you statements.

It's a tradeoff I'm willing to accept as the price of getting the
message through some awfully thick skulls. After all, there are a lot
of dearly held memories of favorite teachers out there, and it's
awfully hard for anyone to admit that some favorite might actually
have led them astray.

For example, what about all those pounds you see in the grocery store?
You've been ignoring them for a long time, haven't you? Or are you
really so god-awful stupid as to think that when we buy and sell goods
by "weight" we'd want to measure some quantity that varies with
location?

PHASE II

Now, let's move on to Phase II of our examination of Sears and
Zemansky. Once again, I'll use the 1970 edition. Feel free to jump
in as show us that they said essentially the same thing in 1956.
Francis Weston Sears and Mark W. Zemansky, University Physics,
Addison-Wesley, 4th ed., 1970.

[page 228 (formula changed to one line)]:

If the system undergoes a temperature change dt,
the specific heat capacity c of the system is defined
as the ratio of the heat dQ to the product of the mass
m and temperature change dt; thus

c = dQ/(m dt)

The specific heat capacity of water can be taken
to be 1 cal g-1 (C°)-1 or 1 Btu lb-1 (F°)-1 for most
practical purposes.

Tell me, what exactly does "lb" mean in this quote?
Hints:
1. Look at what they tell you the denominator is in words. That would
the first quantity identified as part of the "product."
2. Look at the unit in the same position as "lb" in the calories
formula.

[page 230]

Mechanical engineers frequently use the British
thermal unit (Btu), defined as the quantity of heat
required to raise the temperature of 1 lb (mass) of
water from 63°F to 64°F. The following relations hold:

1 Btu = 778.3 ft lb = 252.0 cal = 1055 J.

How much water?

[page 232]

The quantity of heat per unit mass that must be
supplied to a material at its melting point to convert
it completely to a liquid at the same temperature is
called the heat of fusion of the material. The quantity
of heat per unit mass that must be supplied to a
material at its boiling point to convert it completely
to a gas a the same temperature is called the heat
of vaporization of the material. Heats of fusion and
vaporization are expressed in calories per gram, or
Btu per pound. Thus the heat of fusion of ice is
about 80 cal g^-1 or 144 Btu lb^-1. The heat of
vaporization of water (at 100°C) is 539 cal g^-1 or
970 Btu lb^-1. Some heats of fusion and
vaporization are listed in Table 16-2.

Now, it doesn't take a whole lot of genius to figure out what the
quantities are which are measured in those units with the -1
exponents, does it?

But you don't even have to guess. Sears and Zemansky come right out
and tell you. For you and some of the other slow-witted folks in this
thread, here's a hint: Look for the seventh word in each of the first
two sentences, that little word sandwiched in between the words "unit"
and "that." Did you find it?

Do you notice anything strange here? Something different from that
textbook which Keith described for us, which used "lbm" for pounds
mass and "lbf" for pounds force?

Sears and Zemansky, earlier in the book, use the word "pound" and the
symbol "lb" for units of force. But here they are using the word
"pound" and the symbol "lb" for units of mass.

I feel sorry for you if you had to learn physics from idiots like
this. But that still doesn't excuse your ignorance half a century
later; you've had lots of opportunities in the intervening years to
figure out the truth on your own.

Gene Nygaard
Time flies like an arrow;
fruit flies like a banana.