Dutch Roll

Gene Nygaard wrote:

"Julian Scarfe" wrote in message ...
I spent a while writing the physics bit of the New Penguin Dictionary of
Science. The hardest part was knowing whether to be prescriptive (tell them
what the usage *should* be) or descriptive (describe what the common usage
*is*). It's a judgement call in almost every case -- for example, I had no
qualms about defining "weight" quite carefully to distinguish it from
"mass", even though many people say "weight" when they mean "mass".

You are confused if you think you made a correct "should be" call on
this.

Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?

There is no conflict, really, between the call he made, in that context,
and the everyday meaning you go on to defend, and quite convincingly so.

When we say our bag of sugar has, as it might be labeled in the U.S.,
a "net weight" of 10 lb (4.54 kg), where the pound is of course a unit
of mass officially defined as 4.5359237 kg, that is absoloutely
correct and proper, well justified in linguistics, in history, and in
the law.

Absolutely.

That's the original meaning of the word "weight," which entered the
English language meaning the quantity measured with a balance, used to
measure goods sold by weight in commerce. We measures mass, as that
term is used in physics jargon today, with a balance--not the force
due to gravity.

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Where you do have a point is in the sense that this method will give
consistent results whether performed on earth, on the moon, or in any
other gravitational field. Spring-based scales of course measure
absolute weight and will only give correct (mass) results in a
standard gravitational field eg. on the earth's surface.
In both cases we express the result in units of mass.

In other words, it isn't a case of us saying the wrong thing. We mean
to say "weight"; we mean "weight" in a quite legitimate and proper
meaning of the word; it just happens to be the same quantity that
physicists happen to call "mass" in their jargon--but we don't
normally "mean" something different from what we "say."

Agreed. It's not really a case of either being wrong. It's just that
in physics there is a need to differentiate and keep the two concepts
apart, while in everyday life there is normally no such need.

Most people (even physicists, I imagine), quite correctly and
appropriately, say "weight" in everyday contexts, when referring
to something that is really "mass", as the concept is understood
in physics. They are not saying anything different from what
they mean. They are merely applying a level of differentiation
of concepts, appropriate to the situation at hand.

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.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

CV

On Wed, 05 May 2004 13:57:13 +0200, CV wrote:

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics.

There is another issue using this method ... in very critical work,
one compares the volumes of the 2 objects on a balance to correct for
the density of air. The air has lift as did Archimedes system to
determine if some crown was pure gold g (is that the coirrect
reference?)

On Wed, 05 May 2004 21:51:30 -0400, GeorgeB wrote:

On Wed, 05 May 2004 13:57:13 +0200, CV wrote:

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics.

There is another issue using this method ... in very critical work,
one compares the volumes of the 2 objects on a balance to correct for
the density of air. The air has lift as did Archimedes system to
determine if some crown was pure gold g (is that the coirrect
reference?)

Yep, but I think you meant to say bouyancy.

Don

I spent a while writing the physics bit of the New Penguin Dictionary of
Science. The hardest part was knowing whether to be prescriptive (tell
them
what the usage *should* be) or descriptive (describe what the common
usage
*is*). It's a judgement call in almost every case -- for example, I had
no
qualms about defining "weight" quite carefully to distinguish it from
"mass", even though many people say "weight" when they mean "mass".

"Gene Nygaard" wrote in message
om...

You are confused if you think you made a correct "should be" call on
this. ...

I think you illustrate the dilemma rather well! Are there *any* correct
"should be" calls? If so, what makes them "correct"?

I would note however, the words "should be" in the passage below, which you
quote:

'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.'

:-)

Julian

On Wed, 05 May 2004 13:57:13 +0200, CV wrote:

Gene Nygaard wrote:

"Julian Scarfe" wrote in message ...
I spent a while writing the physics bit of the New Penguin Dictionary of
Science. The hardest part was knowing whether to be prescriptive (tell them
what the usage *should* be) or descriptive (describe what the common usage
*is*). It's a judgement call in almost every case -- for example, I had no
qualms about defining "weight" quite carefully to distinguish it from
"mass", even though many people say "weight" when they mean "mass".

You are confused if you think you made a correct "should be" call on
this.

Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?
]
Yes, of science. NOt of the mechanics section of an introductory
physics textbook.

Furthermore, it is often easiest to explain a jargon meaning by
showing how that usage is distinguished from normal usage.

There is no conflict, really, between the call he made, in that context,
and the everyday meaning you go on to defend, and quite convincingly so.

When we say our bag of sugar has, as it might be labeled in the U.S.,
a "net weight" of 10 lb (4.54 kg), where the pound is of course a unit
of mass officially defined as 4.5359237 kg, that is absoloutely
correct and proper, well justified in linguistics, in history, and in
the law.

Absolutely.

That's the original meaning of the word "weight," which entered the
English language meaning the quantity measured with a balance, used to
measure goods sold by weight in commerce. We measures mass, as that
term is used in physics jargon today, with a balance--not the force
due to gravity.

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Pretty strange notion of what it means "to measure" something.

If I have measured forces, then suppose I weighed a gold coin on one
of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
(nearly a troy ounce; the troy units of weight are always units of
mass, never units of force). How much force is it exerting due to
gravity?

Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
much force is it exerting due to gravity here, where the acceleration
of free fall is much less?

If it makes it easier for you, change that to 30.84 g. How much force
does it exert at each place?

If we've measured forces, you should be able to tell me that. But we
haven't "measured" these forces.

Where you do have a point is in the sense that this method will give
consistent results whether performed on earth, on the moon, or in any
other gravitational field. Spring-based scales of course measure
absolute weight and will only give correct (mass) results in a
standard gravitational field eg. on the earth's surface.
In both cases we express the result in units of mass.

In other words, it isn't a case of us saying the wrong thing. We mean
to say "weight"; we mean "weight" in a quite legitimate and proper
meaning of the word; it just happens to be the same quantity that
physicists happen to call "mass" in their jargon--but we don't
normally "mean" something different from what we "say."

Agreed. It's not really a case of either being wrong. It's just that
in physics there is a need to differentiate and keep the two concepts
apart, while in everyday life there is normally no such need.

But the usage in commerce is much more consistent and uniform than the
usage in science.

Most people (even physicists, I imagine), quite correctly and
appropriately, say "weight" in everyday contexts, when referring
to something that is really "mass", as the concept is understood
in physics. They are not saying anything different from what
they mean. They are merely applying a level of differentiation
of concepts, appropriate to the situation at hand.

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.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

Sure, introduce some new big "ifs" not in the original.

As in my example with the gold coin, usually the "gravitation" is not
known. Furthermore, "weighing" the object doesn't give you a "weight"
which is different from mass, as your statement assumes.

The statement in that standard is intended to reflect the fact that
chemists especially, and physicists as well, consider the use of the
verb form acceptable in situations were many would not accept using
the noun "weight" to express the result when they "weigh" something.

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

I think you illustrate the dilemma rather well! Are there *any*
correct "should be" calls? If so, what makes them "correct"?

Precise words = precise thoughts = precise understandings = precise
behavior.

Historical precedent be damned. ;-) Most of history is an example
of slopping thinking.

On Thu, 06 May 2004 14:48:08 GMT, Greg Esres
wrote:

I think you illustrate the dilemma rather well! Are there *any*
correct "should be" calls? If so, what makes them "correct"?

Precise words = precise thoughts = precise understandings = precise
behavior.

So go find yourself a precise word.

Maybe you can borrow one from Norwegian; the physicists using that
language had more sense than those using English. They didn't choose
"vekt"--the cognate of the English "weight"--for their jargon word for
the force due to gravity. Instead, they chose an entirely different
word, "tyngde."

Historical precedent be damned. ;-) Most of history is an example
of slopping thinking.

The meaning of "weight" is much more consistent and uniform in
commerce than it is "in science."

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

Gene Nygaard wrote:
Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?

]
Yes, of science. NOt of the mechanics section of an introductory
physics textbook.

Is physics not science ?

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Pretty strange notion of what it means "to measure" something.

If I have measured forces, then suppose I weighed a gold coin on one
of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
(nearly a troy ounce; the troy units of weight are always units of
mass, never units of force). How much force is it exerting due to
gravity?

Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
much force is it exerting due to gravity here, where the acceleration
of free fall is much less?

If it makes it easier for you, change that to 30.84 g. How much force
does it exert at each place?

If we've measured forces, you should be able to tell me that. But we
haven't "measured" these forces.

Partly true. We have not measured their absolute values. We are not even
interested in them. We have measured the relationship between two forces,
which allows us to determine the mass.

We still depend on there being forces for this measurement to work.
Take your gold coin along on a flight on the Space Shuttle. In a
weightless state, your balance would not tell you anything, but
the coin would still have the same mass as in Hammerfest or Quito.

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.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

Sure, introduce some new big "ifs" not in the original.

As in my example with the gold coin, usually the "gravitation" is not
known. Furthermore, "weighing" the object doesn't give you a "weight"
which is different from mass, as your statement assumes.

It might, and it might not, depending on the method of "weighing".
Use some kind of spring-based scales on your gold coin and it will.

The statement in that standard is intended to reflect the fact that
chemists especially, and physicists as well, consider the use of the
verb form acceptable in situations were many would not accept using
the noun "weight" to express the result when they "weigh" something.

Sure, an elaborate interpretation of what it was "intended to
reflect", to suit your purpose. Didn´t _someone_ just object
to introducing new stuff, not in the original ?

All the same, even in that context, those chemists and physicists
have a good reason for accepting one and not the other, which is
what my comment intended to point out.

CV

On Fri, 07 May 2004 11:48:51 +0200, CV wrote:

Gene Nygaard wrote:
Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?

]
Yes, of science. NOt of the mechanics section of an introductory
physics textbook.

Is physics not science ?

Sure. So what? That might be useful if you want to prove the meaning
we are discussing is _sometimes_ used in science. That's as far as
that logic gets you.

But if you look at the bigger picture, you don't have the consistency
you claimed. Not even in the rest of physics. Not even in real-world
application of those mechanics problems.

Yes, "weight" is sometimes used with that same meaning in other areas
in science. It is also used with other meanings in other areas of
science.

When I first learned about atomic weight, this was different in
physics than it was in chemistry--one based on the oxygen-16 isotope
having an atomic weight of 16, the other on the natural mixture of
oxygen on Earth having an atomic weight of 16.

Don't bull**** me about "molecular weight" and "atomic weight" not
being used any more. Just do a search of the Internet or of Usenet.
Go look at some of the thousands of periodic tables, many from
colleges and universities around the world, which give you the atomic
weight of the elements.

When the medical sciences talk about human body weight, they measure
mass in units of kilograms or pounds, not newtons and not kilograms
force and not pounds force.

It isn't any different if a zoologist talks about the weight of a
capybara or a hummingbird or an ostrich's egg.

What does weight mean when the NASA scientists and engineers tell us
that the weight of the Apollo 11 lunar module at liftoff of its ascent
stage was 10,776.6 lb? At the time, of course, it was only exerting a
force due to gravity of somewhere around 1800 lbf. This is normal
NASA usage; we still see it today in connection with the space
station. For the Apollo missions, NASA has recordings of the
conversations between astronauts and ground control in which the
astronauts are reading off these numbers, in those units of pounds
mass, and they are referring to this quantity as "weight" because
that's the way it was indicated on the readout from their onboard
computers.

An agronomist in the U.S. might use "bushels by weight" in assessing
the production from a test plot of soybeans. That is also "in
science."

Other scientists will measure "dry weight" of various quantities. It
is mass they are interested in, not force.

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Pretty strange notion of what it means "to measure" something.

If I have measured forces, then suppose I weighed a gold coin on one
of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
(nearly a troy ounce; the troy units of weight are always units of
mass, never units of force). How much force is it exerting due to
gravity?

Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
much force is it exerting due to gravity here, where the acceleration
of free fall is much less?

If it makes it easier for you, change that to 30.84 g. How much force
does it exert at each place?

If we've measured forces, you should be able to tell me that. But we
haven't "measured" these forces.

Partly true. We have not measured their absolute values. We are not even
interested in them. We have measured the relationship between two forces,
which allows us to determine the mass.

We still depend on there being forces for this measurement to work.
Take your gold coin along on a flight on the Space Shuttle. In a
weightless state, your balance would not tell you anything, but
the coin would still have the same mass as in Hammerfest or Quito.

So you need to find a different tool when it doesn't work. A liquid
in glass thermometer won't work if it is so hot the glass melts, or so
cold the liquid freezes. But when it does work, we use it to measure
temperature.

NASA has found a different tool for the astronauts to use in weighing
themselves in space.

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.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

Sure, introduce some new big "ifs" not in the original.

As in my example with the gold coin, usually the "gravitation" is not
known. Furthermore, "weighing" the object doesn't give you a "weight"
which is different from mass, as your statement assumes.

It might, and it might not, depending on the method of "weighing".
Use some kind of spring-based scales on your gold coin and it will.

Okay, we've taken care of a couple of the simpler examples. Of
course, there's a reason you don't see gold buyers running around with
spring scales.

Now suppose I have one of those modern piezo-electric electronic load
cell scales, for use in commerce or for precise measurements in the
chemistry lab. Maybe it is used to weigh a bell pepper at the
supermarket, or a semi-load of wheat at the grain elevator, or a
package at the post office.

When it is set up, the manufacturer's representative makes sure that
it is set level, and goes "under the hood" to adjust it for use in
that location. It is, of course, the microprocessor that makes this
possible; making the adjustments is normally made more difficult than
it needs to be, to reduce that chances of tampering when no inspector
is around. He places a known test weight on the scale, and adjusts it
so that it reads the correct amount.

Then when a government inspector comes to test and certify the scale
(in commerce anyway--government doesn't worry about the chemistry
lab), this is done by placing test weights of known mass on the scale,
making sure that the readout is within the limits allowed for the
purpose for which it is used.

So what do those scales "measure"? They are tested and certified on
the basis of their accuracy in measuring mass in the very location in
which they are used, not on their accuracy in measuring force. We
never get any number we could assign to the precise amount of force
the weighed object does exert at that particular location.

Two such scales, properly calibrated, will give the same reading in
Hammerfest and in Quito. Properly adjusted force-measuring scales
would show a significantly different force due to gravity.

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

Bob Moore wrote

Well....a Dutch Roll is probably not what you understand it to be,
particularly if you have not flown swept-wing transport aircraft.
The aileron/rudder drill sometimes taught to student pilots is not
a Dutch Roll.

Well said Bob!

Chuck