SI units in science (Re: Estes' latest ad)
James Wentworth
<< I'm not knocking Bill, as he covers all areas of science & technology and
he is a stickler for the
use of SI units. >>
>Why do you want to ruin kids with those SI units? SI units discourage the
>development of a sense of proprtion. Numbers like 1/4, 1/2, 2, 3 ,4 and 6
>have a real, intrinsic meaning to them that is important to the development
>of design skills in the child's mind. A number like ".317" has no intrinsic
>meaning, it only stimulates the symbolic side of their minds (in that they
>can recognize a "three", a "one" and a "seven". Perhaps the concept
>that the "point" means that the number is less than one rather than
>greater than one has a tiny bit of intrinsic appeal). If all you want
>is a bunch of scientists, OK, but if you want engineers, your not going
>to produce them with units divisible by a meaningless number like ten.
>There are plenty of useful benefits to dividing things into two's,
>three's an four's, but very few to >dividing them in five.
>RE
Rob, I would have agreed with you about this as late as five years ago.
Like every other American pupil, I was taught the US Customary units and
the metric system (Systeme International d'Unites, also known as SI). SI
is an inherently superior system (USC is *not* a system, but a collection
of units) because the units are inter-related. The fundamental SI units are
related by factors of 1 000, not 10 (millimeter, meter, kilometer,
etc.). Units such as the centimeter, which do not follow this
progression, are not used for engineering or scientific purposes. The
centimeter is used for everyday purposes, and because it is derived from
the SI units it is very easy to convert back and forth between
centimeters, millimeters and meters (just mentally move the decimal point).
Wernher von Braun and his team used SI units for all of their
calculations and converted only the final results to USC units, for the
consumption of their American colleagues. Wernher von Braun loathed
inch-pound units and stated so on several occasions.
SI is the metrological language of science, and I applaud Bill Nye for
using it exclusively on his program. Anyone who wishes to understand the
sciences, even at the layman's level, should be acquainted with SI.
America is far more metricated than most citizens realize. Many products
which are labelled in USC units (3.5" floppy diskettes, for example) are
actually made to SI specifications. Forty-three of the state departments
of transportation have converted to SI, and all federal government
buildings are built to SI specifications. All federal government
procurements are to SI standards (including NASA and the armed
services). Next year the federal tax forms will be printed on A4 (the
international standard size) paper.
Like it or not, we live in a metric world.
Jason
--
James J. Wentworth
d005...@dc.seflin.org
The Silent Observer
>
> Next year the federal tax forms will be printed on A4 (the
> international standard size) paper.
Irrelevant to me -- I don't expect to file another paper return in the
foreseeable future. In 1998, for my tax year 1997 return, I paid a
whopping $4.95 to file electronically, after downloading and using
software supplied for free by the filing provider. I had my refund in
hand less than two weeks after uploading the return. I don't intend to
ever go back...
--
WARNING!! This area has been designated an official DOPE FREE ZONE!!
If you're going to be a dope, please do it somewhere else!
Donald Qualls, aka The Silent Observer NAR # 70141-SR Insured
Rocket Pages http://members.aol.com/silntobsvr/launches.htm
Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.
Phil Bulmer
> which are labelled in USC units (3.5" floppy diskettes, for example) are
> actually made to SI specifications. Forty-three of the state departments
> of transportation have converted to SI, and all federal government
> buildings are built to SI specifications. All federal government
> procurements are to SI standards (including NASA and the armed
> services). Next year the federal tax forms will be printed on A4 (the
> international standard size) paper.
>
> Like it or not, we live in a metric world.
>
>
>
>
> Jason
> --
> James J. Wentworth
> d005...@dc.seflin.org
>
>
This is a most interesting thread. It is one of the few instances where the
US is 'following' the UK. Being a child of the late sixties (I missed the
Apollo 11 landing by a week -bummer) I grew up being fully conversant with
both imperial and new 'European' metric units. Inches are fine units of
measurement, they are nice manageable chunks but fractions of an inch are a
real swine. If you look at a scale drawing of a rocket (as I do frequently)
then what the heck is say 10.3"? The figure after the decimal is in base 10
as are 1,000ths of inches. What a cock up! Try drawing a line 10.3" against
a rule, you can't do it! Adding fractions together is not a lot of fun
either!
As for children in school, well I teach 11 to 18 year olds here in the UK
and they don't have any problem with metric. Give them fractions of inches
to both measure and add up and you will see glazed expressions within 30
seconds.
When I was a lad we had pounds, shillings and pence. Nothing was in base 10
and there were 244 pence to the pound. A number of German spies who landed
in the UK during the war were caught out because they didn't understand the
money and would hand over 'pounds' when they were charged an amount in
'shillings' (asking to buy a bottle of cider to take away in a pub on an
east coast beach whilst wearing a suit with the lower 6" (150mm) dripping
wet was another good way of getting caught).
Forget patriotism, we went to metric and it is the best thing we ever did.
If you build scale models then I bet the ones built from metric plans
rather than imperial are just that little bit more accurate in the very
fine detail.
Phil
(My opinions only, if you don't like them divide by 25.4)
MindSpring User
planet earth and it's properties: The meter (metre?) is based on the
circumferance of the earth. The liter (litre?) is based on a volume of
water using the centimeter, at 4 degrees C (one cubic centimeter of water =
1 gram). And so forth. Very sensible, very easy to repeat.
HOWEVER! Two bones of contention.
Firstly, as noted elsewhere, base ten does not lend itself to easy division
by oddball numbers. If I have twelve inches I can easily end up with a
whole number when dividing into 2, 3, 4, or 6, and easy-to-handle
half-inches when 5 or 8 happen. Divide a centimeter by three and you get a
radical. Ouch.
Secondly, and this one really grates me, the kilogram is a measure of MASS
not WEIGHT, and yet we record weight in grams! A kilo of material is still
a kilo, as mass remains constant, even when in zero-g and apparently
weightless. The proper unit to use when measuring the force applied by a
mass due to gravity is Newtons. Man, this detail bugs me, it only serves to
confuse people about the distinction between weight and mass. And yet bacon
is sold by the kilo.
Just my $0.02. Sorry for the lack of rocket content. I'll shut up now.
MindSpring User
MindSpring User wrote in message <73ef2c$pfa$1...@samsara0.mindspring.com>...
>and easy-to-handle
>half-inches when 5 or 8 happen.
Pre-coffee brain burp. Sorry. NOW I'll shut up.
Robert J. Kelley
>It's tough to really knock SI units since they are based entirely on the
>planet earth and it's properties: The meter (metre?) is based on the
>circumferance of the earth. The liter (litre?) is based on a volume of
>water using the centimeter, at 4 degrees C (one cubic centimeter of water =
>1 gram). And so forth. Very sensible, very easy to repeat.
There are some really wonderful consequences of this.
>HOWEVER! Two bones of contention.
>Firstly, as noted elsewhere, base ten does not lend itself to easy division
>by oddball numbers. If I have twelve inches I can easily end up with a
>whole number when dividing into 2, 3, 4, or 6, and easy-to-handle
>half-inches when 5 or 8 happen. Divide a centimeter by three and you get a
>radical. Ouch.
I agree, ouch. Deal with it. It seems to me that Imperial units were
developed on the basis of dividing quantities in half, which is a useful
way to divide things, and an easy division to verify.
>Secondly, and this one really grates me, the kilogram is a measure of
>MASS not WEIGHT, and yet we record weight in grams!
Nobody actually records weight, weight is irrelevant. Any decent scale
actually measures mass, not weight. The distinction in terrestrial
applications isn't that great though. Your bathroom scale probably
wouldn't work well on the moon because it's a spring scale and it
actually measures weight. Your doctor's scale probably would, because
it measures mass.
>A kilo of material is still a kilo, as mass remains constant, even when
>in zero-g and apparently weightless.
True.
>The proper unit to use when measuring the force applied by a mass due to
>gravity is Newtons.
True.
>Man, this detail bugs me, it only serves to confuse people about the
>distinction between weight and mass.
You are one of the confused people, and I know why. It's not your fault.
Your confusion stems from common usage of the verb "to weigh". What it
actually means when you weigh something is that you're measuring its mass.
People wouldn't get confused if it were more common to use the verb "to
mass", as in, "I'm going to mass this bacon". Presto, confusion allayed.
My physics and chemistry teacher always used the verb "to mass".
>And yet bacon is sold by the kilo.
Bacon is sold by mass, not by weight.
This has everything to do with rockets: substitute AP for bacon....
MindSpring User
>>MASS not WEIGHT, and yet we record weight in grams!
>
>Nobody actually records weight, weight is irrelevant.
Lord knows I've tried to tell my wife that...
>Any decent scale actually measures mass, not weight.
<snip>
>You are one of the confused people, and I know why. It's not your fault.
>Your confusion stems from common usage of the verb "to weigh". What it
>actually means when you weigh something is that you're measuring its mass.
>People wouldn't get confused if it were more common to use the verb "to
>mass", as in, "I'm going to mass this bacon". Presto, confusion allayed.
>
>My physics and chemistry teacher always used the verb "to mass".
Whoa, gimme a second, I need to rearrange my thinking. There, that's got
it. I had never considered that a nice beam scale would indeed cancel out
local gravity. Oy. Good one. Beam scale, good. Spring scale, bad.
Thanks, I love it!
>Bacon is sold by mass, not by weight.
...some settling of contents may occur during shipping...
The Silent Observer
>
> Whoa, gimme a second, I need to rearrange my thinking. There, that's got
> it. I had never considered that a nice beam scale would indeed cancel out
> local gravity. Oy. Good one. Beam scale, good. Spring scale, bad.
> Thanks, I love it!
Well, spring scales have their place, too. Since they directly measure
*force* (thanks to Hooke's Law), a well calibrated form of spring scale
(such as a cantilevered mass with strain gages on the beam), with the
bob mass precalibrated against a beam balance in a known acceleration
field (such as that at the surface of the earth) can be used as an
accelerometer. Say, there might even be a rocketry product in that...
B)
In addition, a spring scale (of one sort or another) is exactly what you
want when you're (for instance) measuring the breaking strength of a
piece of line or bungee for use as a shock cord, or when testing the
thrust curve of a rocket motor, or even when applying torque to a bolt
to ensure it's tight, but not too tight (though in that case the spring
scale has to measure force at a calibrated distance from the axis).
And don't forget that a beam balance won't work in microgravity -- what
we used to call "free fall" or "zero G" conditions. For the Skylab
missions, NASA came up with a way to mass astronauts in microgravity:
they put them in a widget that shook them back and forth and used (get
this) spring scales (in this case, in form of strain gages on calibrated
beams) to measure the force needed to accelerate the astronaut at a
measured rate. So, if you're in orbit, "beam balance, bad, spring scale
(with shaker widget) good!"
R. J. Talley
love SI units when doing calculations and measuring is muuuuuuuuuuuuuuuuuuch
easier. However, I hate anything French, wish most European continentals
would go away and never be heard from again, and love to wave my "we kicked
everybody's ass during the world wars flag" . So in short, for teaching
purposes and for utilitarian reasons, I support the metric system and think
we should make it our first priority in schools. But, for purely romantic
and nationalistic/americentric reasons, I like good old pounds, inches and
feet. By the by, has anyone gone above 100 rods with an Estes kit yet?
Reece
NAR 69594
R. J. Talley
English speaking ones are tolerable at best eh? But those Frenchies, geez
Luise, they don't know in from out nor left from right. But some of them,
just one or two mind you, can sing pretty good.
Gene Nygaard
The Silent Observer <sil...@ix.netcom.com> wrote:
> And don't forget that a beam balance won't work in microgravity -- what
> we used to call "free fall" or "zero G" conditions. For the Skylab
> missions, NASA came up with a way to mass astronauts in microgravity:
> they put them in a widget that shook them back and forth and used (get
> this) spring scales (in this case, in form of strain gages on calibrated
> beams) to measure the force needed to accelerate the astronaut at a
> measured rate. So, if you're in orbit, "beam balance, bad, spring scale
> (with shaker widget) good!"
Actually, the device they use is a spring, but not a spring scale. It
measures mass by timing the oscillations of the spring after it is set in
motion; a spring scale measures force by measuring the distance the spring is
extended.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Gene Nygaard
"MindSpring User" <don...@mindspring.com> wrote:
>
> HOWEVER! Two bones of contention.
>
...
>
> Secondly, and this one really grates me, the kilogram is a measure of MASS
> not WEIGHT, and yet we record weight in grams! A kilo of material is still
> a kilo, as mass remains constant, even when in zero-g and apparently
> weightless. The proper unit to use when measuring the force applied by a
> mass due to gravity is Newtons. Man, this detail bugs me, it only serves to
> confuse people about the distinction between weight and mass. And yet bacon
> is sold by the kilo.
A kilogram is a unit of mass, right. But that in no way means that it is not
a unit of weight.
The problem is that weight is an ambiguous word. It means mass more often
than it means one particular kind of force in the jargon of archery, or a
different kind of force in the jargon of physics.
Of course, bacon is sold by the kilogram. (Note that kilo should not be used
as a shorthand version of this unit; kilo- is a prefix which can be attached
to many different units. Use the spelled-out word, or in technical works the
international symbol kg which is recognized in all languages is preferred.)
That's because the net weight in the grocery store is "weight" is its
original meaning, the quantity measured by a gravitational balance which is
mass. To express this weight in newtons would be incorrect.
Consider this from NIST, National Institute of Standards and Technology, the
United States national standards agency (successor to the National Bureau of
Standards:
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
NIST Special Publication 811 (1995 ed.), _Guide for the Use of the
International System of Units (SI)_ by Barry N. Taylor
Or similarly from 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.
Gene Nygaard
http://ourworld.compuserve.com/homepages/weight.htm
| There is another type of measure that is also very
| ancient and that is the measure of mass. . . .
| As time passed, each nation and region developed
| its own standard masses against which unknown masses
| could be compared. The chief such unit is called
| pound in English, from a Latin word meaning "a weight."
| Isaac Asimov
| Realm of Measure,l960
Gene Nygaard
James Wentworth
: However, I hate anything French, wish most European continentals
: would go away and never be heard from again, and love to wave my "we kicked
: everybody's ass during the world wars flag" . So in short, for teaching
If not for the French and other European Continentals (Poles and
Hessians) who helped the 13 colonies during the revolution, we would
probably still be a part of the British Commonwealth today.
: purposes and for utilitarian reasons, I support the metric system and think
: we should make it our first priority in schools. But, for purely romantic
: and nationalistic/americentric reasons, I like good old pounds, inches and
: feet. By the by, has anyone gone above 100 rods with an Estes kit yet?
The metric system is as American as apple pie. Thomas Jefferson,
Benjamin Franklin and John Quincy Adams all strongly endorsed the US
adoption of the metric system, and they had input with the French Academy
of Sciences when the standards for the system were being discussed.
Alexander Graham Bell and Thomas Edison also urged the US to adopt the
metric system (Bell testified before Congress on this subject). Bell,
Edison, Maxwell (a BRITISH scientist, no less) and other American and
European scientists were instrumental in developing the cgs
(centimeter-gram-second) system, a forerunner of today's SI metric system.
All electrical units are metric, and this was established by several
International Electrical Congresses. The US Congress made the metric
system legal for commerce and trade in 1866, and the United States was
one of the signatory nations to the 1875 Treaty of the Meter.
Being a descendant of rather recent British immigrants to the US, I have
no ill feelings towards the United Kingdom. The fact remains, however,
that it is the "US" customary units that are foreign, not the metric
system. If that isn't enough to persuade you, consider this: The Germans
have had an historical dislike for France and things French that rivals the
Anglo-British rivalry, yet Germany enthusiastically embraced the metric
system.
Vamidpowr
>Inches are fine units of
>measurement, they are nice manageable chunks but fractions of an inch are a
real swine.
<Snip>
>Try drawing a line 10.3" against
>a rule, you can't do it!
That depends on your tools. Metric is great, but even so I still design all my
kits using the inch standard, because (being an American over 40) that's how I
think.
The trick is to use an engineer's ruler. Instead of being divided into 16ths,
32nds, etc., this triangular ruler is divided into 10ths, 20ths, etc., up to
60ths of an inch. It also makes scale conversions a snap. Most business
supply stores, many pharmacies, some supermarkets and all college book stores
carry them (at least over here--You may have some difficulty finding them in
the UK). No modeler should be without one.
Chuck Barndt
The Launch Pad
http://www.the-launch-pad.com
Bob Stephenson
MindSpring User wrote in message <73ef2c$pfa$1...@samsara0.mindspring.com>...
Snip
>HOWEVER! Two bones of contention.
>
>Firstly, as noted elsewhere, base ten does not lend itself to easy division
>by oddball numbers. If I have twelve inches I can easily end up with a
>whole number when dividing into 2, 3, 4, or 6, and easy-to-handle
>half-inches when 5 or 8 happen. Divide a centimeter by three and you get a
>radical. Ouch.
>
Okay, I'll bite - what is one fifth of a foot in inches ? How about one
seventh of a yard ? Sorry, but IMHO this argument won't hold rocket fuel
unless you have decifractiphobia (a fear of decimal fractions :^)
>Secondly, and this one really grates me, the kilogram is a measure of MASS
>not WEIGHT,
kerrect...
>and yet we record weight in grams!
not quite right, grams are still only a measure of mass ! Weight is an
imprecise term that refers to the force of gravity on a body and is measured
in Newtons... however the distinction between the two is 'beyond' the
understanding of many people (no flame intended). Hence the common
misconception that 'weight' is measured in grams (or kilograms or tonnes
etc).
Part of the basis of the SI system is the philosophy of using appropriate
units for appropriate applications - I don't think you will find the
astronomic unit (AU) in the SI system but I'm sure it won't go away just
because of that. I could be wrong but I also don't think that the parsec is
SI either (and probably a whole host of other measurements to boot).
<Big cheesy grin>
One thing though, if you guys in the US of A liked Imperial measurements so
much why did you come up with the US gallon ? There must be a good story
there somewhere, anyone out there care to explain ?
</Big cheesy grin>
Cheers
Bob Stephenson
bste...@netspeed.com.au
Canberra, AUSTRALIA
Feel free to visit my model rocketry homepage
http://www.netpseed.com.au/bstephen/NCRHome.htm
"I therefore think I am (but I could be wrong)"
MindSpring User
>One thing though, if you guys in the US of A liked Imperial measurements so
>much why did you come up with the US gallon ? There must be a good story
>there somewhere, anyone out there care to explain ?
></Big cheesy grin>
You made me curious. Here's what I found. It's YOUR fault! We here in the
US were minding our own business, and then boom, you guys across the puddle
up and changed things on us! Hmmph, you can bet I'll be telling that story
to the guy at the gas pump as I fill the tank on my Triumph motorcycle with
it's four (imperial) gallon tank! Makes me wonder, though. For the decade
I've owned this bike I've measured out the oil for the forks in US pints.
Uhoh.
Any way, the story is at
http://members.aol.com/jackproot/met/spvolas.html
and it says:
In England, the Winchester standards were used since the 15th Century. They
were slowly modified, as usual : at the
beginning of the 18th Century, we had a wine gallon containing 231 cubic
inches, an ale gallon of 282 cubic inches and even a
corn ("Winchester") gallon. The bushel was defined at a time as "any round
measure with a plain and even bottom, being 18.5
inches wide throughout and 8 inches deep" (hence its official US definition
: 2150.42 cu.in.)
The Weights and Measures Act of 1824 defined an Imperial British Gallon to
replace all others : it was to contain 10 pounds
of pure water at 62°F (inspired by the decimal system ?) (= 4.5459631
liters).
At the same time in the US, the old wine gallon (also called Queen Anne's
gallon) just discarded in England became the new
official US Gallon (= 3.785411784 liter).
Jimbo Franz
>
> The trick is to use an engineer's ruler. Instead of being divided into 16ths,
> 32nds, etc., this triangular ruler is divided into 10ths, 20ths, etc., up to
> 60ths of an inch. It also makes scale conversions a snap. Most business
> supply stores, many pharmacies, some supermarkets and all college book stores
-- They're called scales, because they scale things from big to little.
They are not rulers.
--Jimbo Franz--
Perspective is everything
Mario Perdue
wrote:
>Vamidpowr wrote:
>>
>> The trick is to use an engineer's ruler. Instead of being divided into 16ths,
>> 32nds, etc., this triangular ruler is divided into 10ths, 20ths, etc., up to
>> 60ths of an inch. It also makes scale conversions a snap. Most business
>> supply stores, many pharmacies, some supermarkets and all college book stores
>> carry them.
>
>-- They're called scales, because they scale things from big to little.
>They are not rulers.
>
No, they're called scales because one definition of "scale" is "a
series of marks used for measuring." Another definition is "an
instrument, as a ruler, that bears such marks." As it happens, an
Engineer's or Architect's Scale is a set of rulers that make it easy
to draw things according to a fixed proportion (also known as scale.)
Mario
NAR #22012
"X-ray-Delta-One, this is Mission Control, two-one-five-six, transmission concluded."
Michael Brown
>
> >and yet we record weight in grams!
>
> not quite right, grams are still only a measure of mass ! Weight is an
> imprecise term that refers to the force of gravity on a body and is measured
> in Newtons... however the distinction between the two is 'beyond' the
> understanding of many people (no flame intended). Hence the common
> misconception that 'weight' is measured in grams (or kilograms or tonnes
> etc).
In US Customary Units, mass and force are numerically
the same, which is not the case in SI. There is a
conversion constant, g_c, that converts lb_m ft/s^2
into lb_f.
Force [=] lb_f (pounds-force)
Mass [=] lb_m (pounds-mass)
g_c = 32.2 (lb_m*ft/s^2)/lb_f
g = acceleration due to gravity
g/g_c = 1 lb_f/lb_m (at sea level)
F*g_c = m*g
F = m * g/g_c
In the vernacular, the subcripts for force and
mass are dropped, leaving lb (pound) for both
mass and weight. As you have already noted, most
people don't know the difference.
-Mike
R. J. Talley
graduate degree in American History I know all the stuff about where and
when the US got involved with the metric system, it's good to see others do
too. I'm also very much aware to what degree and why, several European
countries added to our revolution. So, my anti-Europe remarks are just so
much hyperbole. Whip me with a wet meter stick!
Reece
Jimbo Franz
>
> On Wed, 25 Nov 1998 23:12:28 -0800, Jimbo Franz <in...@usrockets.com>
> wrote:
>
> >-- They're called scales, because they scale things from big to little.
> >They are not rulers.
> >
>
> No, they're called scales because one definition of "scale" is "a
> series of marks used for measuring." Another definition is "an
> instrument, as a ruler, that bears such marks." As it happens, an
> Engineer's or Architect's Scale is a set of rulers that make it easy
> to draw things according to a fixed proportion (also known as scale.)
-- That fixed proportion is what make it a scale. It is never a ruler, a
ruler is for measuring at 1:1 scale only. ;<)
Steve Olson
Jimbo Franz wrote in message <365D7F3A...@usrockets.com>...
>....a ruler is for measuring at 1:1 scale only. ;<)
A ruler is the titular leader of a country (°¿°)
Gene Nygaard
"Bob Stephenson" <bte...@netspeed.com.au> wrote:
>
> <Big cheesy grin>
> One thing though, if you guys in the US of A liked Imperial measurements so
> much why did you come up with the US gallon ? There must be a good story
> there somewhere, anyone out there care to explain ?
> </Big cheesy grin>
>
> Cheers
>
> Bob Stephenson
> bste...@netspeed.com.au
> Canberra, AUSTRALIA
It's quite simple. We didn't change! It is you who were still associated
with Britain in the 1820s who changed to a completely new, "imperial" gallon.
We in the United States stuck with much older units; Queen Anne's wine
gallon for liquids--she had a prodigious capacity for the stuff ;-) We stuck
with other old English units, the Winchester gallon (seldom used by that
names any more, just quarts and pints or fractions of a bushel or peck) and
bushel for dry commodities.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/internat.htm
Bob Stephenson
MindSpring User wrote in message <73ij4r$dg8$1...@camel0.mindspring.com>...
>><Big cheesy grin>
>>One thing though, if you guys in the US of A liked Imperial measurements
so
>>much why did you come up with the US gallon ? There must be a good story
>>there somewhere, anyone out there care to explain ?
>></Big cheesy grin>
>
the
>US were minding our own business, and then boom, you guys across the puddle
>up and changed things on us! Hmmph, you can bet I'll be telling that story
>to the guy at the gas pump as I fill the tank on my Triumph motorcycle with
>it's four (imperial) gallon tank! Makes me wonder, though. For the decade
>I've owned this bike I've measured out the oil for the forks in US pints.
>Uhoh.
>
Great stuff ! I tell the guys that I work with regularly that I read rmr
for all the interesting things I learn (well, apart from all the POL and
FLAME rubbish that is). This just goes to confirm my opinion of the group -
good one MindSpring, I stand a little the wiser for your efforts :^).
Just one question though, why do you refer to the Pacific Ocean as the
puddle ? Ohhhh, you have us confused with our English cousins ! You know
it's really quite easy to tell us apart - aside from the way we mangle the
language that is. We're the ones with plenty of wide open space and sunny,
calm weather suitable for rocket flying :^)) (at least I hope so this
Summer).
Cheers
Bob Stephenson
bste...@netspeed.com.au
Canberra, AUSTRALIA
Feel free to visit my model rocketry homepage
dracomi...@my-dejanews.com
reference manual with its engines rated in "kilograms of thrust"!?! They're
just taking SI an making the same mistakes with it that the EE system makes.
On a related topic, to speak of the specific impulse of a rocket motor in
"seconds" is confusing and incorrect. In US units, it is measured in
lbf-seconds/lbm, at which time people cross out both "pounds" and say
"seconds" but lbf and lbm are not equivalent. I much prefer Isp measured in
Newton-seconds/kilogram as it was intended. How many Newton-seconds will you
get from each kilogram of propellant? Pretty obvious if I just said the Isp
of the propellant was 2100 Newton-seconds per kilogram. If I expressed the
Isp in seconds, what does *that* tell you?
Cheers,
Joe
Robert J. Kelley
> On a related topic, to speak of the specific impulse of a rocket motor in
>"seconds" is confusing and incorrect. In US units, it is measured in
>lbf-seconds/lbm, at which time people cross out both "pounds" and say
>"seconds" but lbf and lbm are not equivalent. I much prefer Isp measured in
>Newton-seconds/kilogram as it was intended. How many Newton-seconds will you
>get from each kilogram of propellant? Pretty obvious if I just said the Isp
>of the propellant was 2100 Newton-seconds per kilogram. If I expressed the
>Isp in seconds, what does *that* tell you?
It's interesting, but Isp in seconds means something intuitive to me.
that a hypothetical rocket could exert thrust commensurate with its weight
for a given number of seconds; it could exert a force equal to the force of
gravity on itself. Isn't that slightly more meaningful (on earth) than
ns/kg? Maybe just a little?
All this aside, I'd just plain be happier if rocketry used SI units, if for
nothing more than a vehicle to integrate SI-awareness into the rest of my
life.
Robert Kelley
TRA #6399 L2
Portland, OR
RobEdmonds
seventh of a yard ?>>
That's the point. One fith and one seventh are proportions that are basically
useless for design purposes. 2, 3 and 4 are useful. I spend hours sitting
here trying to figure out how to separate 12 or 24-inch pieces of wood into a
whole bunch of pieces that will fit together in various laminations and
symmetrical assemblies. This depends entirely on there being simple, regular
proportions at all levels in the design process. There just isn't time to pull
out a calculator every time I move a line or make a decision. I have to be
able to know instantly that, for example, I can fill 3/8 of an inch with either
two 3/16" sheets or three 1/4" sheets. You just can't do that if you have a
buch of stuff made in 5 and 2 and a bunch of long strings of digits to
interpret every time you want to compare something. There is rarely ever a
reason to divide something by 5, yet the metric system bends over backwards to
let you do it at the expense of all the other potential dividends. It's fine
for science or academics, but if you're actually out there trying to design
somebody a kit with it, the metric system just doesn't make any sense.
RE
Gene Nygaard
dracomi...@my-dejanews.com wrote:
> It always makes me chuckle a little when I see a foreign jet aircraft in a
> reference manual with its engines rated in "kilograms of thrust"!?! They're
> just taking SI an making the same mistakes with it that the EE system makes.
Nobody's taking SI and making the same mistakes here. What they are using is
kilograms force which were considered acceptable before the introduction of
the International System of Units in 1960. It is not acceptable in SI.
Sometimes the problem is that they are converting from pounds, and the proper
conversion factors for pounds force to newtons are not well enough
publicized. A lot of people, and especially rocket scientists, seem
blissfully unaware that pounds are used to measure two different quantities.
In that case, I'd say that the problem lies with the use of the English
customary units, not with the metric units.
>
> On a related topic, to speak of the specific impulse of a rocket motor in
> "seconds" is confusing and incorrect. In US units, it is measured in
> lbf-seconds/lbm, at which time people cross out both "pounds" and say
> "seconds" but lbf and lbm are not equivalent. I much prefer Isp measured in
> Newton-seconds/kilogram as it was intended. How many Newton-seconds will you
> get from each kilogram of propellant? Pretty obvious if I just said the Isp
> of the propellant was 2100 Newton-seconds per kilogram. If I expressed the
> Isp in seconds, what does *that* tell you?
>
> Cheers,
> Joe
I agree with you there (except, of course, newtons should not be spelled with
a capital letter in English).
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
The Silent Observer
Well, as it happens, if you multiply by G (whether you use 32.2 ft/s^2
or 9.81 m/s^2, doesn't matter) it will give you the effective exhaust
velocity, which is a pretty useful thing to know in some
circumstances...
Mark Fields
> <<Okay, I'll bite - what is one fifth of a foot in inches ? How about one
> seventh of a yard ?>>
>
> That's the point. One fith and one seventh are proportions that are basically
> useless for design purposes. 2, 3 and 4 are useful. I spend hours sitting
> here trying to figure out how to separate 12 or 24-inch pieces of wood into a
> whole bunch of pieces that will fit together in various laminations and
> symmetrical assemblies. This depends entirely on there being simple, regular
> proportions at all levels in the design process. There just isn't time to pull
> out a calculator every time I move a line or make a decision.
> I have to be
> able to know instantly that, for example, I can fill 3/8 of an inch with either
> two 3/16" sheets or three 1/4" sheets.
I think perhaps it would be "two 3/16" sheets" or "three 1/8" sheets"????
Jimbo Franz
>
> <<Okay, I'll bite - what is one fifth of a foot in inches ? How about one
> seventh of a yard ?>>
>
> That's the point. One fith and one seventh are proportions that are basically
> useless for design purposes. 2, 3 and 4 are useful. I spend hours sitting
> here trying to figure out how to separate 12 or 24-inch pieces of wood into a
> whole bunch of pieces that will fit together in various laminations and
> symmetrical assemblies. This depends entirely on there being simple, regular
> proportions at all levels in the design process. There just isn't time to pull
> out a calculator every time I move a line or make a decision. I have to be
> able to know instantly that, for example, I can fill 3/8 of an inch with either
> buch of stuff made in 5 and 2 and a bunch of long strings of digits to
> interpret every time you want to compare something. There is rarely ever a
> reason to divide something by 5, yet the metric system bends over backwards to
> let you do it at the expense of all the other potential dividends. It's fine
> for science or academics, but if you're actually out there trying to design
> somebody a kit with it, the metric system just doesn't make any sense.
> RE
-- Because you chose to work in inches doesn't mean another system
doesn't make sense. If you purchased ply in metric thickness, metric
would make sense. I can fill 9mm with three 3mm or one 6mm and one 3mm
sheets. How much more simple and regular can proportions get than
tenths, hundredths, tens, hundreds, etc.?
Bob Stephenson
MindSpring User wrote in message <73o79m$o02$1...@camel18.mindspring.com>...
Snip...
>
>Ooooh, you're an Ausie! Sorry 'bout that. And that means summer is just
>around the bend for you, while I sit here above the equator checking my
>furnace and sharpening my snow shovel. I'm so jealous of you right now
that
>I'm gonna say that this whole gallon thing is STILL your fault. So there.
>
>Actually, I hope you have a wonderful, safe, and high flying summer.
>
>Have fun.
>
Yeah, I'm one of the Colonial club... and yes, we are heading into summer
right now :^) My only problem is that the wind is being unkind at the
moment.
I spent the Winter buried in computer science study (I'm not only a bar but
also a bas (born again student ?)) and have managed to crib a little time to
build the 'Southern Cross'. She is based on the Quest 'Icarus' but all that
is left of the original is the body tube and nose cone. I have retro fitted
a 'D' motor mount with hand made stainless steel engine hook, ttw fins made
of 0.8 mm ply AND an ejection baffle system just like the old Centuri
designs. The paint job is all white with a silver nose cone and custom
colour decals.
The only thing not completed yet is the lugless launch system - I have yet
to figure out how that one is going to work. All in all this is a great
looking rocket (IMHO ;^) and should fly great if I can ever get some calm
weather to launch it.
RobEdmonds
I think perhaps it would be "two 3/16" sheets" or "three 1/8" sheets"????>>
See? It's so intuitive I can't even tranlate it into typing correctly.
RE
Gene Nygaard
> >
> > If I expressed the
> > Isp in seconds, what does *that* tell you?
>
> Well, as it happens, if you multiply by G (whether you use 32.2 ft/s^2
> or 9.81 m/s^2, doesn't matter) it will give you the effective exhaust
> velocity, which is a pretty useful thing to know in some
> circumstances...
>
Seems to me that that is exactly the point that Joe (dracomissile22) is
making. His newton-seconds per kilogram are dimensionally equivalent to
meters per second. The conversion factor between them is 1.
That's what is useful. So why mess around with useless pseudoseconds which
are really lbf s/lbm, if you need to remember the value of small italic g
(not G, which is something different) to use them?
Mark Simpson
> I spent the Winter buried in computer science study (I'm not only a bar but
> also a bas (born again student ?)) and have managed to crib a little time to
> build the 'Southern Cross'. She is based on the Quest 'Icarus' but all that
> is left of the original is the body tube and nose cone. I have retro fitted
> a 'D' motor mount with hand made stainless steel engine hook, ttw fins made
> of 0.8 mm ply AND an ejection baffle system just like the old Centuri
> designs. The paint job is all white with a silver nose cone and custom
> colour decals.
Don't forget to get yourself a copy of Crosby, Stills and Nash's song by
the same name for background mood music. It's a classic.
Mark Simpson
NAR 71503 Level II
MindSpring User
>Just one question though, why do you refer to the Pacific Ocean as the
>puddle ? Ohhhh, you have us confused with our English cousins ! You
know
>it's really quite easy to tell us apart - aside from the way we mangle the
>language that is. We're the ones with plenty of wide open space and sunny,
>calm weather suitable for rocket flying :^)) (at least I hope so this
>Summer).
Mark Johnson
>
>
> Seems to me that that is exactly the point that Joe (dracomissile22) is
> making. His newton-seconds per kilogram are dimensionally equivalent to
> meters per second. The conversion factor between them is 1.
Yup...strictly speaking, specific impulse should be expressed
in terms of characteristic exhaust velocity (abbreviated c* in
the literature, including Sutton).
The basic equation (derived, I think, by Hermann Oberth) for
velocity increase due to a rocket motor is:
v = c* x log (mass ratio)
e
where of course
mass ratio = (rocket mass + fuel mass)/rocket mass
If you don't have a calculator that does Naperian logarithms,
and you want to express the thing in terms of specific impulse,
the way I learned the equation was:
v = Isp x g x 2.303 x log(mass ratio)
This of course is in vacuum, and can equally well be stated
as 'delta v' for a rocket already in motion.
--
Mark Johnson LSI Logic Storage Systems, Inc.
M/S 18 (formerly Symbios, Inc.)
mark.j...@lsil.com 3718 N Rock Road
(316)636-8189 Wichita, KS 67226-1397
dracomi...@my-dejanews.com
The Silent Observer <sil...@ix.netcom.com> wrote:
> dracomi...@my-dejanews.com wrote:
> >
> > If I expressed the
> > Isp in seconds, what does *that* tell you?
>
> Well, as it happens, if you multiply by G (whether you use 32.2 ft/s^2
> or 9.81 m/s^2, doesn't matter) it will give you the effective exhaust
> velocity, which is a pretty useful thing to know in some
> circumstances...
>
Exactly. Isp in N-s/kg is equal to the characteristic exhaust velocity in
m/s. When I see Isp expressed in seconds anywhere, I always multiply it by
10 in my head to get a ballpark figure for N-s/kg anyway, but why use the
incorrect nomenclature in the first place? If you like the old units, it
would be correct to express Isp in lbf-s/slug or even lbf-s/lbm, but not
"seconds."
Cheers,
Joe
Jimbo Franz
>
> Show me one place in nature where a ratio that is a power of ten occurs. I can
> show you millions made from say, powers of six (honeycombs, snowflakes, packing
> cylinders closely, molecular stuctures, inscribed hexagon in a circle using the
> radius of the circle as the length of a leg, etc.). You can do the same for
> 2, 3, 4 and probably 12. You'll get nowhere with 10. It ain't even really how
> many fingers we have, those other two are really thumbs. If we were cartoon
> charaters and had eight fingers, then the metric system might be all right.
> But it would be even better to have six. Ten is just a basically useless
> number.
> RE
-- Metric was designed as an integrated system for description (size,
volume, mass, etc.) of man-made, easily scalable items. Rockets come
immediately to mind. If I were designing a flower, fractals would be the
choice for easy scaling. Pi is everywhere, would you care for a Pi based
counting system (it did have it's uses in ancient Egypt)?
What if you want to scale your design up one third?
"Let's see, 7/8 times 1.333333 is..., 7*1.3333 = 9.3333, no, that won't
work..., 8*3 = 24, 7*3 = 21*1.333 = 28, so... 28/24-24 = 1 4/24, shoot,
my ruler is in 16ths and 32nds, 4/24 = 1/6, there's the 6 I was looking
for on the snowflake project..., let's see, 1/6" is 1/72nd of a foot...,
reminds me of an airplane model I built once..., maybe I'll make that
first measurement 3/4". Yes, 1.333*3/4 = 1". We don't need no stinking
metric system!"
All in good fun,
Mario Perdue
wrote:
>[snip]
>
>What if you want to scale your design up one third?
>
>"Let's see, 7/8 times 1.333333 is..., 7*1.3333 = 9.3333, no, that won't
>work..., 8*3 = 24, 7*3 = 21*1.333 = 28, so... 28/24-24 = 1 4/24, shoot,
>my ruler is in 16ths and 32nds, 4/24 = 1/6, there's the 6 I was looking
>for on the snowflake project..., let's see, 1/6" is 1/72nd of a foot...,
>reminds me of an airplane model I built once..., maybe I'll make that
>first measurement 3/4". Yes, 1.333*3/4 = 1". We don't need no stinking
>metric system!"
>
>[snip]
Or you could use your 'scale,' you know... the one with the six
'rulers,' and measure it directly. :^)
RobEdmonds
9mm with three 3mm or one 6mm and one 3mm
sheets.>>
That's fine until you get numbers less than one involved. Now, you could
assume that mm's are fine enough that you would only have to make integral
sizes, making that workable. But as for:
<<How much more simple and regular can proportions get than tenths, hundredths,
tens, hundreds, etc.?>>
Show me one place in nature where a ratio that is a power of ten occurs. I can
PeteAlway
>Show me one place in nature where a ratio that is a power of ten occurs. I
can
>show you millions made from say, powers of six (honeycombs, snowflakes,
packing
>cylinders closely, molecular stuctures, inscribed hexagon in a circle using
the
>radius of the circle as the length of a leg, etc.). You can do the same for
>2, 3, 4 and probably 12. You'll get nowhere with 10. It ain't even really
how
>many fingers we have, those other two are really thumbs. If we were cartoon
>charaters and had eight fingers, then the metric system might be all right.
>But it would be even better to have six. Ten is just a basically useless
>number.
Rob, you have made an excellent case for dumping base 10. As long as nobody
hacks off any of my supernumary philanges, I could go for a switch. After all,
computers do very well in base two. And once we make the conversion in our
numbering system, fractions will be easier. None of this 8 13/32 junk. Just
1000.01101, which would be a buttload easier to read off a ruler.
But unless you are willing to dump decimal counting, decimal units make more
sense.
I wonder if the people who came up with english units were really decimal
counters. I mean counting is really just a chant of nonsense words--Wun Tou
Thri Fore Faiv Siks Sehvun Ate Nain Tehn Ulevin Tuellv (beyond that it's base
ten talking with crazy polysyllabic words like tuennisehvun and
ahunerdnsickstiate, which do not a chant make)--not unlike Eenie Meenie Miney
Moe--just remember the chant word you hit when you run out of cows or
Phillips-head rocks or whatever. So you just rember that you chant all the way
to tuellv as you place knuckles end to end to get a foot. Chant to miney when
you lay barleycorns to get a standard knuckle since Ogg's knuckles are bigger
than Kell's... Altogether a fine way of measuring when everyone counts by
chant, without bases.
So Yeah, base twelve or base 8 or base 2 would be nice if our numbering system
worked that way.
And if I can keep all my fingers.
Peter Alway
Remove a couple .com's from address to reply. Check
out the Saturn Press website for my rocketry books and posters:
http://members.aol.com/satrnpress/saturn.htm
Stefan Wimmer
>Why do you want to ruin kids with those SI units? SI units discourage the
>development of a sense of proprtion. Numbers like 1/4, 1/2, 2, 3 ,4 and 6
>have a real, intrinsic meaning to them that is important to the development
>of design skills in the child's mind. A number like ".317" has no intrinsic
>meaning, it only stimulates the symbolic side of their minds (in that they
>can recognize a "three", a "one" and a "seven". Perhaps the concept
>that the "point" means that the number is less than one rather than
>greater than one has a tiny bit of intrinsic appeal). If all you want
>is a bunch of scientists, OK, but if you want engineers, your not going
>to produce them with units divisible by a meaningless number like ten.
>There are plenty of useful benefits to dividing things into two's,
>three's an four's, but very few to >dividing them in five.
>RE
Hi Rob (et al.)
please admit that I (grown up in a SI world) find this kind of argumentation
very funny!
Having enjoyed (and still enjoying) how units interact in the SI system
without any cumbersome factors (except natural constants) I can only smile
about your argumentation - without any intend to look conceited!
The SI system is a really SYSTEMATIC array of units whereas the US/UK system
seems to me more like a collection of separately defined units (like we had in
the middleage throughout Europe too).
It is amazing how almost all formulas in rocketry are based on meters,
kilograms and seconds.
--
Stefan Wimmer Cellware Broadband
Email s...@cellware.de Rudower Chaussee 5
WWW http://www.cellware.de/ 12489 Berlin, Germany
Visit my private Homepage: Love, Electronics, Rockets, Fireworks!
http://www.geocities.com/CapeCanaveral/6368/
The Silent Observer
>
<snip very amusing treatment of measurments>
>
> So Yeah, base twelve or base 8 or base 2 would be nice if our numbering system
> worked that way.
>
> And if I can keep all my fingers.
Well, Peter, if we change over to binary, we can maximize the value of
counting on our fingers, not to mention forever consigning Chisanbop to
the dusty hall of hacks and work-arounds. Just think, we can teach
children how to do twos complement arithmetic in first grade, how to add
binary amounts in kindergarten, and produce a generation who find
programming in assembler as easy as many of our kids find Web research.
Of course, we'll have to get used to spending $101.1111101... for things
that used to cost $7.98. Shouldn't be any harder than converting from
English (aka US Customary) to SI (aka metric), right? B)
Andy Eng
Just my last message for the day,
Stefan Wimmer wrote:
>
> Rob Edmonds <RobEd...@aol.com>
> >Why do you want to ruin kids with those SI units?
<ctrl-x>
> The SI system is a really SYSTEMATIC array of units whereas
Systematic, yes... Natural, no...
"Pi" is natural, so is "e", as are 1-2-3 and 3-4-5 triangles...
BTW, IMO, binary, octal & hex is anti-humane ;-)
Regards,
Andy
Jimbo Franz
>
> On Tue, 01 Dec 1998 23:03:13 -0800, Jimbo Franz <in...@usrockets.com>
> wrote:
>
> >[snip]
> >
> >What if you want to scale your design up one third?
> >
> >"Let's see, 7/8 times 1.333333 is..., 7*1.3333 = 9.3333, no, that won't
> >work..., 8*3 = 24, 7*3 = 21*1.333 = 28, so... 28/24-24 = 1 4/24, shoot,
> >my ruler is in 16ths and 32nds, 4/24 = 1/6, there's the 6 I was looking
> >for on the snowflake project..., let's see, 1/6" is 1/72nd of a foot...,
> >reminds me of an airplane model I built once..., maybe I'll make that
> >first measurement 3/4". Yes, 1.333*3/4 = 1". We don't need no stinking
> >metric system!"
> >
> >[snip]
>
> Or you could use your 'scale,' you know... the one with the six
> 'rulers,' and measure it directly. :^)
-- That's not fair: it's a base ten system and was "ruled" unacceptable
earlier. And it's for a "kit", do you require the purchase of a scale to
build the kit? "The kit is free, but the scale is gonna cost ya." ;<)
DWard
><<But unless you are willing to dump decimal counting, decimal units make
more
>sense.>>
>
>approximation of something.
actually, I find it the reverse, but ya gotta limit yourself to the number
of digits that represent the actual precision of your measurements...
nothing like recording measurements to the millionth of an inch when using a
wooden yardstick :-)
>A fraction has a philosphical resonanace to it,
>whereas a decimal has, at the VERY best, some sort of woeful, bleak
>practicality.
What I don't understand is why folks SI only with decimal usage and ancient
english units with fractions? You can use fractions or decimals regardless
of your measurement system, they are independent.
-Dave "Okay, I've said my say, now I'll go back to trying to stuff a 1/2 kg
of AP into a 1.134 diameter rocket..." Ward
Jimbo Franz
>
> Fractions make you happy, they make you think of a bright sunny day and slicing
> up a pie or your birthday cake or something. A fraction is true, whereas a decimal always feels like an
> approximation of something. A fraction has a philosphical resonanace to it,
> whereas a decimal has, at the VERY best, some sort of woeful, bleak
> practicality.
-- Ah, a true believer. I will leave you to your delusions now. ;<)
RobEdmonds
What if you want to scale your design up one third?
"Let's see, 7/8 times 1.333333 is..., 7*1.3333 = 9.3333, no, that won't
work..., 8*3 = 24, 7*3 = 21*1.333 = 28, so... 28/24-24 = 1 4/24, shoot,
my ruler is in 16ths and 32nds, >>
Man, you couldn't even get through the first line without putting a decimal in
there. You guys are just addicted to ten!
Incidentally, my mother gave me an architect's scale that had 24ths and 48ths
on it when I was little, and I must have used it a thousand times. No, I mean
1296 times!!
RE
RobEdmonds
sense.>>
My bags fit a one foot piece of wood, so I never have to count higher than 12,
so the decimalness of numbers has basically no impact on me. Plus, if you had
to use fractional decimal numbers to design, I probably wouldn't do it.
Fractions make you happy, they make you think of a bright sunny day and slicing
up a pie or your birthday cake or something. Decimals make you think of the
IRS. How can you POSSIBLY use them? It's uncanny, if you watch me at the CAD,
you'll see that nowhere in any of these planes will I put in a dimension that
is not an even fraction of an inch, even if I'm typing a decimal in for
precision positioning, even when I'm setting an incidence or working with some
arbitrary part that doesn't touch anything else. There are plenty of 64th's in
those planes. A fraction is true, whereas a decimal always feels like an
approximation of something. A fraction has a philosphical resonanace to it,
whereas a decimal has, at the VERY best, some sort of woeful, bleak
practicality.
RE
By the way, what happened to the drawing and physics education thread? I never
found it again.
RobEdmonds
without any cumbersome factors (except natural constants)>>
I just spent a whole article explaining that they do not do so. Ten is the
most "cumbersome factor" imaginable. It has no place anywhere in the design
world. There is no significance of any kind for the number ten in the design
world. Any measurement system based on the number ten is by definition the
barbaric poppycock of idle minds! And then:
<<It is amazing how almost all formulas in rocketry are based on meters,
kilograms and seconds.>>
They're not "based" on those in any way, the physics is completely independant
of what units we choose to quantify it with. All the rockets built in this
country were designed with English units, and flew DEMONSTRABLY better for it.
RE
I hope he doesn't hold me to that "demonstrably".
PeteAlway
>All the rockets built in this
>country were designed with English units, and flew DEMONSTRABLY
>better for it.
I should say here that I hold Mr. Edmonds in high esteem, as a gentleman and a
scholar who puts his money where his mouth is on some well thought-out ideas on
rocketry and education, and his design skills leave me in awe.
But this is *demonstrably* the silliest thing I've ever heard you say.
>I hope he doesn't hold me to that "demonstrably".
same here.
Peter "how many cubic inches to a pint? No fair looking it up!" Alway
Scott McCrate
Oh, well that explains it then. Rob is an aesthete. A poet. We see sharply
designed boost gliders, he sees gently wafting balsa birds. Teach us master! You
are indeed the philosopher king of boost gliders! [Teasing, but just slightly
;0). Thanks for the awesome designs.]
Scott McCrate NAR 71680
smcc...@nospam.tui.edu
mccr...@nospam.fuse.net (remove nospam. to respond by e-mail)
doug holverson
>designed boost gliders, he sees gently wafting balsa birds. Teach us master! You
>are indeed the philosopher king of boost gliders! [Teasing, but just slightly
>;0). Thanks for the awesome designs.]
>
-DGH-
Mike Pearson <see .sig>
> Peter "how many cubic inches to a pint? No fair looking it up!" Alway
American or British? Dry or liquid? <g>
--
Mike
NAR #70953 - Sr/Insured/Level-1 ~ SeaNAR - The Seattle NAR Section #568
NO Junk Email, please! Real email to: amphoto [at] blarg [dot] net.
<WARNING: Do not look into laser beam with remaining eye!>
RobEdmonds
of digits that represent the actual precision of your measurements...>>
If there are three apples and you eat two of them, you didn't eat .6667 of
them.
RE
RobEdmonds
english units with fractions? You can use fractions or decimals regardless
of your measurement system, they are independent.>>
Because a third of a foot is 4 inches, whereas a third of a decimeter is
something unworkable.
RE
RobEdmonds
Why is it that whether it is the English measurement system or the Macintosh
computer, the users thereof are characterized as some kind of "believers" or
"zealots". I use both of these things as a purely practical decision. There
would be too much time and effort to design these kits in the decimal system,
and there would be too much time and effort to draw them, create instructions
for them and store business information about them if I used a Windows
computer. You guys keep trying to attribute this stuff to some kind of
passionate desire, when in fact, I keep demonstrating every day that you need
English units and Macintosh computers to successfully design a series of
pleasing enjoyable kits. It is a totally practical decision. The evidence is
right here that these things benefit you in accomplishing the tasks you want to
accomplish, yet people want to dipute this as though I'm wishing on fairies or
something.
RE
RobEdmonds
>designed boost gliders, he sees gently wafting balsa birds.>>
That's actually pretty good.
RE
RobEdmonds
Nonsense. If you put a rocket designed with English units against a metric
one, the efficiency will be two to three times as high. So high, in fact, that
escape velocity is not required. I mean, that always was a myth anyway.
RE
RobEdmonds
which which self-satire began.
RE
Dave Lyle
I like your common sense approach to this Rob.
When they figure out how to get 100 degrees in a circle, 100 seconds in
a minute, 100 minutes in an hour, 100 hours per day, and 100 days per
years, then I'll consider going metric. :-)
--
Dave
NAR 69845 Lvl 1, WOOSH
The Silent Observer
Well, it's a fairly ugly number to write, but in practice, I'd like to
see anything this side of a laser cutter make two pieces, one 33 mm and
the other 33.33 mm in length, accurately enough that I can put them side
by side and tell the difference (much less put three of them end to end
and miss the missing millimeter).
Now, if I'm matching them up with a slot cut to the same accuracy, with
traditional methods, I'm as likely to have the piece too short and the
slot too long as vice versa -- but in the die cut era, you'd compensate
for that by intentionally cutting the piece a millimeter too long, and
including an instruction to dry fit and sand to exact size. Given that
wood changes dimension with changes in humidity, and that different
pieces change different amounts (even over the same gauge length), I'd
rather see even laser cutting done this way -- though the amount the tab
needs to be bigger than the slot can be much less with this kind of
accurate cutting, and a kit with this kind of precision fit probably
should also specify which side to sand on.
OTOH, if you're calling out a dimension for a laser cutter, what's wrong
with 33.33 mm? You're just about matching the positioning accuracy of
the beam spot on the wood, after all.
To put it bluntly, I don't care how or if you measure anything anywhere
in the kit, or if you lay it all out in a loft like ship designers used
to do, including springing a batten -- as long as the pieces fit and the
end result is stable in boost and glides well, I'll probably like it.
At least until I try to clone it... B)
PeteAlway
>them.
>RE
Nor did you eat half of them, or 3/4 of them, or 5/8 of them, or 11/16 of them,
or 21/32 of them, or 43/64 of them.
But I had to use a slide rule to get those fractions. I know how to
approximate 2/3 arbitrarily well in decimal without calculating or looking it
up.
Peter Alway
PeteAlway
>Because a third of a foot is 4 inches, whereas a third of a decimeter is
>something unworkable.
>RE
What's a third of eight inches? In conventional base-2 fractions, not thirds
of inches.
PeteAlway
>I keep demonstrating every day that you need
>English units and Macintosh computers to successfully design a series of
>pleasing enjoyable kits.
We're not on your case for *using* English units. We're on your case for
asserting metric is a bad thing.
Hell, I use english units and Macintosh computers for damn near everything I
do. It's because I am intimate with the Mac and Macdraw Pro--they do exactly
what I want them to do--that I am sticking to them. I lay out books and other
documents in English units. But when I am drawing up an Ariane or a V-2, I use
metric units. When I build a scale model, I use the units of the
prototype--metric or English. When I design my own, I may use metric, I may
use English, but I usually just wing it and don't worry about measurements. If
I want to calculate rocket performance, I use metric units
I have no doubt that you can put a man on the Moon using English units. But I
don't think you *have* to use english units. You have proven that you can
design wonderful gliders in English units, but it's silly to think that one
can't do it in metric. Similarly, someone could write rocketry books on a
Windows machine--maybe someone has. English system and Macintosh are matters
of cultural or personal preference. The fact that english units are a cultural
preference means that as individuals, we are stuck with them by upbringing and
common usage around us, and may use them despite personally seeing they have
big flaws. The biggest problem with choices our culture makes for us is that
we are in danger of thinking that because everyone around us does things a
certain way, it's the right way. And there is certainly a practical benefit to
conforming. If you aren't on a morl high horse about systems of units, it's
probably best to conform to the system that's conventional in the application
in question.
That the Macintosh is a personal choice means we have made the decision to load
a lifetime of files on a mac, and while we may have this sinking feeling that
our favoirte tool may disappear from the market, we chose our tool on a
rational basis. I can't afford to throw $2000 at computer stuff every year (I
am convinced that this is considered the "normal" budget, considering the
software and hardware capabilities people keep assuming I have), so my mac is
it. Metric and English rulers are a lot cheper.
Your assertion that English units are a functioning system for design is an
obvious truth. To assert that Metric is any less functional is silly.
To claim that the Soviets failed to reach the moon because they built the N1 in
metric units would be as silly as claiming they *succeeded* in launching the
first satellite because they built the R-7 in metric units.
Peter "more rambling..." Alway
PeteAlway
>one, the efficiency will be two to three times as high. So high, in fact,
that
>escape velocity is not required. I mean, that always was a myth anyway.
>RE
In a world where pounds are pounds, Mass = Force = Money, and as in cartoons,
anything can happen.
Peter Alway
doug holverson
----------
In article <19981204000411...@ng137.aol.com>, robed...@aol.com
(RobEdmonds) wrote:
><<What I don't understand is why folks SI only with decimal usage and ancient
>english units with fractions? You can use fractions or decimals regardless
>of your measurement system, they are independent.>>
>
>Because a third of a foot is 4 inches, whereas a third of a decimeter is
>something unworkable.
How about a third of an inch?
>:)
-DGH-
doug holverson
----------
In article <19981204001437...@ng137.aol.com>, robed...@aol.com
(RobEdmonds) wrote:
><<-- Ah, a true believer. I will leave you to your delusions now. ;<)>>
>
>Why is it that whether it is the English measurement system or the Macintosh
>computer, the users thereof are characterized as some kind of "believers" or
>"zealots". I use both of these things as a purely practical decision. There
>would be too much time and effort to design these kits in the decimal system,
>and there would be too much time and effort to draw them, create instructions
>for them and store business information about them if I used a Windows
>computer. You guys keep trying to attribute this stuff to some kind of
>passionate desire, when in fact, I keep demonstrating every day that you need
>English units and Macintosh computers to successfully design a series of
>pleasing enjoyable kits. It is a totally practical decision. The evidence is
>right here that these things benefit you in accomplishing the tasks you want to
>accomplish, yet people want to dipute this as though I'm wishing on fairies or
>something.
>RE
Well, in nine years as a Mac user, I've had less trouble than my step-dad
has had with his p.o.s. Packard Bell in the past nine days. After setting up
a couple old USAF-surplus 486 machines to run non-Mac rocket software, I can
say that megahertz to megahertz, my old Performa 6200 has ten times less
hassle and twice the computer. So Mac use is less than a matter of faith
then the Wintel world would have you believe.
BTW- You MR hobbyests should write or port more software to the Mac.
OTOH- I think that the Metric system is more practical, but I use U.S.
(SAE?) measurements when making my stuff only because it's more familar to
me. When I write up the lit, I convent it into metric because that is
supposed to be the offical system of model rocketry.
-DGH-
DWard
><<actually, I find it the reverse, but ya gotta limit yourself to the
number
>of digits that represent the actual precision of your measurements...>>
>
>them.
If the recipe for my fuel-air explosive bomb* requires a 1/2 bag of flour
(when's the BATF going to regulate that; it's been responsible for more
structural explosions in the US than terrorist have!); I just kinda eyeball
it into two approximately equal lots; if on the other hand, it requires .5
bag, out come the scales... In your example above, it's the same thing; I
use fractions when I'm not being exact (approximately 2/3rds of the total
mass of apples has been consumed) and decimals when I need greater than
eyeball precision.
But again, what has this got to do with using or not using SI units? You
can use fractions in SI unit measurements just as you can use decimals in
SAE (stupid acient english?) unit based measurements.
Dave "Okay, I've said it again, now I'll go back to trying to stuff a 1/2 kg
of AP into a 1.134 inch diameter rocket..." Ward
--*just kidding.
____________________________________________________________________________
__
Dave
Opinions herein are mine and not my company's;
They are shareware, if you like them, send me $20.00, if you don't send me
your $0.02
Remove the nuclear device to reply
RobEdmonds
them,
or 21/32 of them, or 43/64 of them.
But I had to use a slide rule to get those fractions. I know how to
approximate 2/3 arbitrarily well in decimal without calculating or looking it
up.>>
Why did you feel a need to "get" those fractions? Why the compulsion to
determine their decimal equivalent. Your supposed to use them the way they
are: two thirds, the ratio of two to three, which is the same for everyone in
the world, no matter what the precision of any calculating apparatice they
might own. The real number is this ratio, this .66667 is just some means to
try to express a similar quantity in a numbering system that isn't really up to
the task to begin with. Two out of three is it, that is what it is, you don't
have to get it, you got it right there, it, it done already got gotten, what
else do you need?
RE
RobEdmonds
use fractions when I'm not being exact (approximately 2/3rds of the total
mass of apples has been consumed) and decimals when I need greater than
eyeball precision.>>
I didn't say anything about "mass of apples", I said "apples". You ate EXACTLY
two thirds of the apples. Don't you guys understand where numbers came from in
the first place? Now as for the case of the bags of flour, that's entirely a
matter of your own habits, I see no reason why "1/2" should call for any less
precision in measurement than ".5".
RE
RobEdmonds
anything can happen.>>
Which is precisely what is wrong with SciFi action movies.
RE
RobEdmonds
you can
design wonderful gliders in English units, but it's silly to think that one
can't do it in metric.>>>>
I believe, and there is know way to prove this emperically because I'm not
going to try this the other way, that I save a significant amount of time and
effort by designing in the English system, and that this saving results from
the fact that it has been designed to be subdivided into useful fractional
units. It is also true that if it took much more time to do this stuff than
it actually does, I probably would not attempt it. Therefore, as a practical
measure, something like the English system MUST exist for me to do this.
RE
The Silent Observer
Well, when I learned about "precision" (in high school physics in 1974
-- and I'm pretty certain this hasn't changed in 24 years), we would
certainly have treated 0.5 as more precise that 1/2. The decimal number
0.5 implies a precision of +- 0.05, or half of the implied precision of
the measurement, which in this case is to the nearest tenth. The
fraction 1/2, on the other hand, implies a precision to the nearest
quarter -- that is, 1/2 +- 1/4.
Now, if you wanted to write in a decimal (for instance, in a machining
spec), but imply lower precision than the decimal number would normally
carry, you'd do it the way scientists and engineers do; you'd write
something like 0.5 +- 0.25; that's equivalent to saying "we measured
this as five tenths, but we only have confidence in our measurement to
the nearest twenty-five hundredths." OTOH, if you need to express a
fraction (for instance, to convey a simple ratio, admittedly hard to do
well with decimals) with higher precision, the engineering and machining
method is to write it as an unsimplified fraction of the required
precision -- for instance, we might write 32/64 to imply we measured to
the nearest 1/64 and it was still 1/2.
If you specify 1/2" without saying somewhere in the spec that "all
measurements are to the nearest 1/64 inch" you've asked for all your
pieces to be between 1/4" and 3/4" in size -- which might work nicely
for lumber, but won't work well at all for making gliders. OTOH, if you
specify 12.5 mm +- 0.5 mm, you'll get all your pieces between 12.0 mm
and 13.0 mm, which will put them all within just over 1/64" of the size
you really want, without spending money to reject the ones that are more
than 12.6 mm or less than 12.4 mm after cutting. If that's not a tight
enough tolerance, cut it to +- 0.2 mm, and you're getting a spread of
almost exactly 1/64" total -- and in the meantime, you can do most of
you work with whole numbers of millimeters.
The Silent Observer
>
> (RobEdmonds) wrote:
>
> >Because a third of a foot is 4 inches, whereas a third of a decimeter is
> >something unworkable.
>
> What's a third of eight inches? In conventional base-2 fractions, not thirds
> of inches.
>
Near enough for a carpenter's cut (which my dad always said was the
nearest 1/32"), that'd be 2 11/32" -- if you want to do it in
semiprecision machinist's fractions, it'd be 2 21/64" instead. Either
one will be off by less than the precision of the measurement after
putting three pieces cut to that precision end to end. Either one will
waste more material in the cut kerfs than is lost in measurement error.
Either one is as exact as using a decimal of real world precision to
accomplish the same approximation.
Bill Westfield
English system, and that this saving results from the fact that it has
been designed to be subdivided into useful fractional units.
So what are common "scale factors", anyway? 1/48, 1/64, 1/300, 1/125 ?
I don't see how those work out nicely in either metric or english units.
(OTHO, I sorta like scale factors like 1mm=1inch, 1cm = 1 foot, etc...)
If you're really into fractions (power-of-two fractions, anyway), you
could just dispense with units altogether and use graphical methods to
produce your ratio'ed parts. I've done this in some drawings for things
only peripherally related to rockets. Pick lengths an units for the
drawing that work out conveniently, and then adjust the pixel/print
scaling so that the printed image comes out in an appropriate size. In
this day of computers and calculators, it seems pretty silly to use
english measurements cause they're easier to divide by three, or metric
measurements cause they're easier to divide by 10...
BillW
--
(remove spam food from return address)
PeteAlway
>are: two thirds, the ratio of two to three, which is the same for everyone in
>the world, no matter what the precision of any calculating apparatice they
>might own.
I don't have a ruler with thirds of inches marked. Haven't seen any in the
store. I guess there may be an archetect's scale that has them if I go to the
right fractional scale and figure out how may inches at 1/48 scale comeout to
1/3. But I can't find one in my house. Lots of metric rulers, though,
including one with 3-d spaceships (including an astronaut doing an EVA from a
silver Mercury capsule) and one with a picture of a Saturn V (thanks George
Gassaway) and one with "National Association of Rocketry" in gold letters.
Thirds of inches are a pain with English rulers, but thirds of centimeters are
pretty easy.
Peter Alway
PeteAlway
>I don't see how those work out nicely in either metric or english units.
Common model scale factors are:
1/220 (railrad Z-scale)
1/160 (railroad N Scale)
1/144 (Plastic Airliners;12 feet to the inch)
1/100
1/96 (Revell Apollo; eight feet to the inch)
1/87 (railroad HO scale)
1/76 (plastic tanks)
1/72 (Plastic aircraft; six feet to the inch)
1/48 scale (Plastic aircraft; "quarter [inch] scale" to some; O scale to model
railroaders. 4 feet to the inch) (by the way, if O is 1/48, why is half-O or
HO, 1/87. )
1/35 scale (plastic tanks)
1/32 scale (Plastic aircraft; 1/2^5)
1/24 scale (Plastic aircraft, maybe cars, too; two feet to the inch)
1/16 scale (plastic cars, I think; 1/2^4)
1/12 scale (dollhouse; one inch to the foot)
(and others I don't know or can't think of)
So some standard scales are very much tied to the English system.
Model rockets are scaled to diameters, so there are no standard scales, though
1/100 is favored for Saturns. No system of units is preferable when scaled to
a body tube at some funky scale, though if you use a calculator, a decimal
system (decimal inches or metric) is easier.
RobEdmonds
slot too long as vice versa -- but in the die cut era, you'd compensate
for that by intentionally cutting the piece a millimeter too long, and
including an instruction to dry fit and sand to exact size. Given that
wood changes dimension with changes in humidity, and that different
pieces change different amounts (even over the same gauge length), I'd
rather see even laser cutting done this way -- though the amount the tab
needs to be bigger than the slot can be much less with this kind of
accurate cutting>>
The one thing in there that you will never see, of course, is an instruction
to sand to fit in one of my kits (except a couple of absolutely unavoidable
places, like that Deltie hook). But whereas you mention some compenatory
actions that are no longer required in lazer cutting, there are also a few new
ones. You used to be able to thing of a die blade as basically widthless, the
wood re-expanding to fill where it was displaced after the blade is removed.
The laser on the other hand leaves a finite "kerf" in the wood. Were I to
REALLY do things right, I would actally make all of the tabs a bit bigger (or
the slots a little smaller) to allow for this. One day when there is really a
lot of time, I plan to go through all the kits and add the necessary hundreth
of an inch or so that is needed at these locations.
RE
RobEdmonds
of inches.>>
That's true (meaning, the point you were making by asking this), but in the
other system you cant even do the case for the whole foot. The point of mine
is that, since there are twelve-inch feet in the english system, you are likely
to get a piece of wood 24, 36 or 48 inches long which can be divided many
useful ways and still leave you with integers (that are easy to think about),
whereas with the metric system you are likely to end up with a piece of wood
that is 50,100 or 150 cm long, which can not (with the possible exception of
the 150 cm one which is pretty versatile, but you still end up with 25's, 30's
and the like insted of 2,3,4,6,8,12). I just don't like long abstract numbers,
I like the kind of numbers that I can recognize instantly when I see a dot
pattern on a domino. The shape of those patterns tells you some of the things
that the numbers are for. For example, "six" is for laying out a grid of tiles
half again as long as it is wide. Then if you build a square on the long side
of that, you get the same shape again. Helps you landscape, among other
things.
RE
RobEdmonds
one will be off by less than the precision of the measurement after
putting three pieces cut to that precision end to end. Either one will
waste more material in the cut kerfs than is lost in measurement error.>>
Quite true that by the time you get down to the cutting, the precision is lost.
I'm more speaking of purity of thought in the initial design process. It's
just a lot less cluttered in your head when you have things expressed in the
form of the ratio you're interested in rather than the corresponding string of
decimal digits.
RE
The Silent Observer
Of course, that's a matter of personal preference. Personally, I find
it purer not to mess with fractions at all. How many dimensions on the
average rocket really need to be finer than a millimeter?
RobEdmonds
are
pretty easy.>>
In what way? It's just as easy for me to make a mark at "about five and a
third sixteenths" as it is for you to make one at "about three and a third
milimeters". But the real point is that I can say a third, half, fourth, sixth
or twelfth of a foot and come out with an exact integer. You can't do ANYTHING
like that in metric. It's people that complain about having twelve rather than
ten inches in a foot that I'm really talking about.
RE
RobEdmonds
enough tolerance, cut it to +- 0.2 mm, and you're getting a spread of
almost exactly 1/64" total -- and in the meantime, you can do most of
you work with whole numbers of millimeters.>>
That's almost not so bad.
RE
RobEdmonds
the scale guy. For the scale guy, with the arbitrary tube diameters he
mentioned, decimal systems indeed win.
RE
RobEdmonds
Obviously, except on architect's scale, there is no third of inch mark, but
neither is there in metric. In no case except for fifths and tenths, which are
pretty useless design-wise, does metric offer a mark where english does not.
Dave/Kristin Hall
: Obviously, except on architect's scale, there is no third of inch mark, but
: neither is there in metric. In no case except for fifths and tenths, which are
: pretty useless design-wise, does metric offer a mark where english does not.
One comment: I've seen much discussion about the "ease" of designing based
on whether or not the primary unit can be divided an integer number of times
(whatever your integer of choice may be). I find this strange. In my line
of work, I do a *LOT* of scaling.... but I *NEVER* change units. Meaning,
if the original design was measured in feet, the new design is measured in
feet. It makes no difference how many inches that is.... Ditto for meters.
I work with either system *constantly* (DoD says all new systems must be
metric but older systems tend to be English...I work with both new and old
systems every day). I find neither system to be harder/easier to work
with. They are, after all, arbitrary units of measure.
--
David Hall
Missile Performance Office (Code 476H00D)
Naval Air Warfare Center - Weapons Division
China Lake, CA 93555
RobEdmonds
it purer not to mess with fractions at all. How many dimensions on the
average rocket really need to be finer than a millimeter?>>
Depending on the meaning of "average rocket", either none or several. Most of
my precision needs come either from trying to fit various combinations of
notched parts, trying to fit institutional tube and cone sizes inside things
(like square fusalages), and trying to fix the incidence setting. Really, the
fractional arithmetic only offers an advantage in the first of those three.
RE
RobEdmonds
on whether or not the primary unit can be divided an integer number of times
(whatever your integer of choice may be). I find this strange. In my line
of work, I do a *LOT* of scaling.... but I *NEVER* change units. Meaning,
if the original design was measured in feet, the new design is measured in
feet. It makes no difference how many inches that is....>>
It's not so much for the purpose of scaling, it's more for making parts fit,
getting certain numbers of parts out of a single sheet, making laminations,
what have you. There are dozens of situations that come up in every kit design
effort in which a lot of simple arithmetic is needed, which is just much easier
to perform "on the fly" when you know that all your wood sizes, thicknesses,
and measurement system are based on simple proportions.
RE
Philip Doolittle
most people never experience a change in gravitational attraction, weight often
assumed to be the same as mass Force in either system is properly mass x
accelleration. In the US system mass is not the same as force (weight). Mass in
the US system is measured in an rarely heard quantity known as 'slugs'.
Weight [=] lb (pounds) or N (newtons)
Mass [=] sl (slugs) or kg (kilograms)
Accelleration [=] ft/ (sec * sec) or m/sec*sec
g [=] Accelleration value of gravity at the earths surface (32.2 ft/sec * sec or
9.8m/s^2)
F= m*a i.e. weight = force
Example: I weight 180#/ 81.8kg. My mass is 5.59slugs/ 801 N.
Michael Brown wrote:
> Bob Stephenson wrote:
> >
> > >and yet we record weight in grams!
> >
> > not quite right, grams are still only a measure of mass ! Weight is an
> > imprecise term that refers to the force of gravity on a body and is measured
> > in Newtons... however the distinction between the two is 'beyond' the
> > understanding of many people (no flame intended). Hence the common
> > misconception that 'weight' is measured in grams (or kilograms or tonnes
> > etc).
>
> In US Customary Units, mass and force are numerically
> the same, which is not the case in SI. There is a
> conversion constant, g_c, that converts lb_m ft/s^2
> into lb_f.
>
> Force [=] lb_f (pounds-force)
> Mass [=] lb_m (pounds-mass)
> g_c = 32.2 (lb_m*ft/s^2)/lb_f
> g = acceleration due to gravity
> g/g_c = 1 lb_f/lb_m (at sea level)
>
> F*g_c = m*g
> F = m * g/g_c
>
> In the vernacular, the subcripts for force and
> mass are dropped, leaving lb (pound) for both
> mass and weight. As you have already noted, most
> people don't know the difference.
>
> -Mike
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Philip Doolittle
Since the relationship between weight and mass is direrctly proportional, and
most people never experience a change in gravitational attraction, weight often
assumed to be the same as mass Force in either system is properly mass x
accelleration. In the US system mass is not the same as force (weight). Mass in
the US system is measured in an rarely heard quantity known as 'slugs'.
Weight [=] lb (pounds) or N (newtons)
Mass [=] sl (slugs) or kg (kilograms)
Accelleration [=] ft/ (sec * sec) or m/sec*sec
g [=] Accelleration value of gravity at the earths surface (32.2 ft/sec * sec or
9.8m/s^2)
F= m*a i.e. weight = force
Example: I weight 180#/ 801 N. My mass is 5.59slugs/ 81.8kg.
Michael Brown
>
> ...Mass in
> the US system is measured in an rarely heard quantity known as 'slugs'.
Close, but not quite. The slug is the unit of mass of the
British system, and pound_mass, as I stated earlier, is the
unit of mass in the USCS.
-Mike
Gene Nygaard
pdoolittle...@mindspring.com wrote:
> CORRECTION: BIG TYPO....
Looks to me as if the typos are still there, and what was changed was a
bigger lapse in your thinking. But at least you now have the SI units in
their proper places, with kilograms for mass and newtons not mass.
>
> Since the relationship between weight and mass is direrctly proportional,
and
> most people never experience a change in gravitational attraction, weight
often
> assumed to be the same as mass
I probably would have said something similar 10 or 20 years ago. But now this
bashing of "the people" has gotten to be one of my pet peeves. It isn't "the
people" who get it wrong, but those who've had some strange ideas pounded into
their head in an introductory-level physics course.
Weight is not just assumed to be the same as mass--that is the original
meaning of weight, and it remains the meaning which is almost always used
today in commerce. It is a quite proper and legitimate meaning of the word.
The people who use the word "weight" with this meaning have prior claim to it
by more than 700 years over those who use it in a physics jargon sense,
limited to a particular kind of force.
> Force in either system is properly mass x accelleration.
True.
>In the US system mass is not the same as force (weight).
Mass is not the same as force. But weight might mean either mass, or one
particular kind of force in archery jargon, or a different kind of force in
physics jargon.
>Mass in
> the US system is measured in an rarely heard quantity known as 'slugs'.
These slugs are a 20th century invention, not used in any physics books before
about 1940, and not used in physics books now since most of them use SI
units, and not used to any significant extent anywhere outside the U.S. at any
time, though they originated in the early 1900s in the British aeronautics
industry.
What do you suppose the English units of mass were before the slug was
invented? Where do poundals fit in? (Hint: they are not a part of any system
which uses slugs.) What are the proper units of mass when poundals are used?
What do you think the English units of mass are today, since you "rarely hear"
slugs? See, for example, either Encyclopædia Britannica or World Book
Encyclopedia, both of which do define a slug but neither of them expresses a
single measurement in their entire works in slugs. Don't you think they have
any measurements of mass in these encyclopedias? (The same is likely true of
others, including various CD titles, but I'm confident in making these very
strong statements about the contents of these two particular encyclopedias.)
>
> Weight [=] lb (pounds) or N (newtons)
Force can be in pounds force (lbf) or poundals (pdl) or newtons (N) or
various other ounces and tons and whatever.
Consider this definition:
weight The force with which gravity acts on a body. Weight is
correctly measured in poundals or newtons, but not in pounds
or kilograms because the weight of a body may vary depending
on the magnitude of the force of gravity, whereas the mass of
of the body, which is measured in pounds or kilograms, does
not change. Weight is equal to mass multiplied by the
acceleration due to gravity (g). At Earth's surface,
1 pound has a weight of about 32.2 poundals. In metric
units, a mass of 1 kilogram has a weight of about
9.8 newtons.
_Physics Today_, World Book Encyclopedia of Science, 1991 printing
(copyrght 1984, 1989 Verlagsgruppe Bertelsmann International).
The text of this book uses metric units, but the part on Gravity at p.
50 has a sidebar including these conversion factors:
1 kilogram = 2.20 pounds
1 newton = 7.23 poundals
It's just as wrong as, but no more than, what you and even some introductory
level physics textbooks say. This makes exactly the same error, but with the
opposite results. Each is mistakenly assuming that the units peculiar to one
particular system of mechanical units have something to do with the use of
English units in general. They just chose different systems of mechanical
units as the jumping-off point to get to these erroneous conclusions.
> Mass [=] sl (slugs) or kg (kilograms)
Mass can be in kilograms (kg) or in pounds (lb, the most common English units
of mass) or slugs (slug).
The primary, legal definitions of pounds are and always have been as units of
mass.
When the United States, Canada, the United Kingdom, Australia, New Zealand,
and South Africa got together in 1959 to agree on a common definition, they
defined this pound as a unit of mass exactly equal to 0.45359237 kg. For 66
years before that in the United States, this pound had been defined as a
slightly different fraction of a kilogram. Before the definition in terms of
the kilogram, all the various pounds used throughout history had been units
of mass based on independently maintained national standards of mass.
Don't you think that all the experts in the field involved in these decisions
knew what they were doing? Weren't all these metrologists well aware of the
difference between mass and force?
> Accelleration [=] ft/ (sec * sec) or m/sec*sec
Put parentheses in on the latter as well:
m/(s*s) or m/s^2, where s is the proper symbol for seconds
> g [=] Accelleration value of gravity at the earths surface (32.2 ft/sec * sec
or
> 9.8m/s^2)
> F= m*a i.e. weight = force
>
> Example: I weight 180#/ 801 N. My mass is 5.59slugs/ 81.8kg.
You weigh (not weight) 180 lb, which is equivalent to 5.5 slugs or 82 kg.
These are the proper units for human body weight, various science museum
exhibits about your "weight" on various planets notwithstanding. The
kilograms used throughout the world for this are the proper units, but
physicists just don't bother to stop and think about which factor is more
important to human health. It isn't a clear-cut decision, because the force
factors also do come into play--but it is often in forces from other sources
than gravity, such as when you are running or when you run into a football
player. The Body Mass Index is properly named (this is the mass in kilograms
divided by the square of the height in meters, or in the much more
complicated formula often given to Americans, mass in pounds multiplied by
some hard-to-remember number and divided by the square of the height in
inches)_.
The force your 180 lb body will exert on Earth, due to the resultant of
gravitational forces and centrifugal force, can be expressed as 5800 poundals
or as 800 newtons, or it might also be expressed as 180 pounds force.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/weight.htm
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Bob Kaplow
> Doing upscales with English units SUCKS!
>
> My solution is I have a steel rule which is in inches - one side
> 1/64ths, the other 1/100ths.
Or invest in a micrometer, and stick to DOWNscales.
Bob Kaplow NAR # 18L TRA # "Ctrl-Alt-Del"
Kaplow Klips: http://members.aol.com/myhprcato/KaplowKlips.html
NIRA: http://www.nira.chicago.il.us NAR: http://www.nar.org
SPAM: u...@ftc.gov postm...@127.0.0.1 otherwise, I'm not on MARS!