Error in constants documentation?
Hello, http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says: dyn one dyne in watts lbf one pound force in watts kgf one kilogram force in watts doesn't the watts actually have to newtons as the unit of force? Regards, Florian
Florian Lindner wrote:
Hello,
http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says:
dyn one dyne in watts lbf one pound force in watts kgf one kilogram force in watts
doesn't the watts actually have to newtons as the unit of force?
There is a ticket with the same question here: http://projects.scipy.org/scipy/ticket/1001 Warren
Regards,
Florian _______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
Warren Weckesser wrote:
Florian Lindner wrote:
Hello,
http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says:
dyn one dyne in watts lbf one pound force in watts kgf one kilogram force in watts
doesn't the watts actually have to newtons as the unit of force?
There is a ticket with the same question here: http://projects.scipy.org/scipy/ticket/1001
Warren
Fixed in trunk by r6310. Thanks for pointing out the mistake. Warren
It would seem that there is some confusion, in the constants.html, between force and mass... Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things). So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass). This is absent from the constants page. Regards, AMG Warren Weckesser wrote:
Florian Lindner wrote:
Hello,
http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says:
dyn one dyne in watts lbf one pound force in watts kgf one kilogram force in watts
doesn't the watts actually have to newtons as the unit of force?
There is a ticket with the same question here: http://projects.scipy.org/scipy/ticket/1001
Warren
Regards,
Florian _______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
_______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass). This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass. Regards, Florian
Regards,
AMG
Warren Weckesser wrote:
Florian Lindner wrote:
Hello,
http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says:
dyn one dyne in watts lbf one pound force in watts kgf one kilogram force in watts
doesn't the watts actually have to newtons as the unit of force?
There is a ticket with the same question here: http://projects.scipy.org/scipy/ticket/1001
Warren
Regards,
Florian _______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
_______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
Wed, 07 Apr 2010 19:02:49 +0200, Florian Lindner wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
One of the headings should, strictly speaking, say "Mass" instead of "Weight". -- Pauli Virtanen
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de>wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass)<http://en.wikipedia.org/wiki/Slug_%28mass%29>. This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler. Chuck
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <charlesr.harris@gmail.com
wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de>wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass)<http://en.wikipedia.org/wiki/Slug_%28mass%29>. This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.") DG
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <d.l.goldsmith@gmail.com>wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris < charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de>wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass)<http://en.wikipedia.org/wiki/Slug_%28mass%29>. This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
Well, what if someone wants to know what a slug is in SI units? It's not as if it is a big problem to support, and the more conversions the better, IMHO. The point of having these things down in code is that one doesn't have to go looking when the unit turns up somewhere. Chuck
On Wed, Apr 7, 2010 at 11:40 AM, Charles R Harris <charlesr.harris@gmail.com
wrote:
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <d.l.goldsmith@gmail.com>wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris < charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de>wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass)<http://en.wikipedia.org/wiki/Slug_%28mass%29>. This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
Well, what if someone wants to know what a slug is in SI units? It's not as if it is a big problem to support,
I think as time drags on it will become a bother to support; if someone needs Imperial support, they can roll their own. DG
and the more conversions the better, IMHO. The point of having these things down in code is that one doesn't have to go looking when the unit turns up somewhere.
Chuck
_______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
-- Mathematician: noun, someone who disavows certainty when their uncertainty set is non-empty, even if that set has measure zero.
On Wed, Apr 7, 2010 at 13:57, David Goldsmith <d.l.goldsmith@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:40 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <d.l.goldsmith@gmail.com> wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de> wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass). This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
Well, what if someone wants to know what a slug is in SI units? It's not as if it is a big problem to support,
I think as time drags on it will become a bother to support; if someone needs Imperial support, they can roll their own.
They're constants. The amount of support they need is smaller than the smallest function in our codebase. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco
Oh wohl, I tried. DG On Wed, Apr 7, 2010 at 12:03 PM, Robert Kern <robert.kern@gmail.com> wrote:
On Wed, Apr 7, 2010 at 13:57, David Goldsmith <d.l.goldsmith@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:40 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <
d.l.goldsmith@gmail.com>
wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de
wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene: > It would seem that there is some confusion, in the > constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
> Strictly speaking, kg is a unit of mass, Newton a unit > of force. Weight is force, not mass: A gold brick > floating in interstellar space is weightless but still > massive. Pounds and kilograms can be equated, but only > in some specified gravitational field (like at the > surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and
kilograms
could be equated in any context. Pound itself is ambigous.
> So mass is the more fundamental quantity, since it does > not depend on gravity for its value. In Imperial units > (feet, pounds) the unit of mass is the slug: > http://en.wikipedia.org/wiki/Slug_(mass)<http://en.wikipedia.org/wiki/Slug_%28mass%29>. This is > absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
Well, what if someone wants to know what a slug is in SI units? It's not as if it is a big problem to support,
I think as time drags on it will become a bother to support; if someone needs Imperial support, they can roll their own.
They're constants. The amount of support they need is smaller than the smallest function in our codebase.
-- Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user
-- Mathematician: noun, someone who disavows certainty when their uncertainty set is non-empty, even if that set has measure zero.
Dear John, I once read that the Beagle (the Mars spacecraft ) crashed because some engineer forgot to convert inches to metres, or the other way around. Since people use python at nasa, it might even be an improvement to remove the English units rather than to keep them in :-) bye NIcky On 8 April 2010 00:14, John Hassler <hasslerjc@comcast.net> wrote:
On 4/7/2010 2:40 PM, Charles R Harris wrote:
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <d.l.goldsmith@gmail.com> wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de> wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass). This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
Well, what if someone wants to know what a slug is in SI units? It's not as if it is a big problem to support, and the more conversions the better, IMHO. The point of having these things down in code is that one doesn't have to go looking when the unit turns up somewhere.
Chuck
I think you're always going to have to (in effect) look up the units ... or at least understand what they are doing.
Back when I was a productive member of society, I used to teach this stuff. English units of mass and force are very difficult, and here's why. Someone, back in the dim dark reaches of history, before even I can remember, decided that one pound mass (lbm) should WEIGH one pound force (lbf). Now, Newton said that F = M*A ... force = mass times acceleration. The natural unit for acceleration in English units is foot/sec**2, so we would naturally expect that: l lbf = 1 ft/sec**2 * 1 lbm. BUT .... weight is the force caused by the acceleration of gravity, and 1 lbm WEIGHS 1 lbf, so: 1 lbf = (32.174 ft/sec**2)*1 lbm.
There seems to be a little problem here. (Metric units _define_ force in terms of mass and acceleration, so this difficulty doesn't arise. English units try to fix more variables than there are available degrees of freedom.) There are two alternative ways to fix it. One is to choose a more rational system of units. The other is to use a fudge factor. English engineers, naturally, chose the latter.
The most common "fix" in Chemical Engineering is to define a fudge factor, the "gravitational constant," gc, such that: force (lbf) = acceleration (ft/sec**2)*mass(lbm)/gc. So gc = 32.174 ft lbm/(lbf sec**2)
(Another "fix" is to use mass in terms of "slugs," where a "slug" is the mass which is accelerated by 1 ft/sec**2 by a force of 1 lbf. So a slug = 32.174 lbm. This doesn't seem to be used much any more.)
The units problem is a real stumbling block for engineering students whenever we use English units (which is most of the time, in American industry). Some equations require gc, and some don't, and it isn't always obvious which is which. Sometimes "lbm" is hidden. For example, viscosity "contains" lbm ... except of course, if we use kinematic viscosity, which doesn't ... so equations containing viscosity need to have gc, except when they don't.
And, of course, Murphy's law applies.
john
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On 7 April 2010 14:32, David Goldsmith <d.l.goldsmith@gmail.com> wrote:
On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <charlesr.harris@gmail.com> wrote:
On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <mailinglists@xgm.de> wrote:
Am Dienstag, 6. April 2010 22:08:53 schrieb Arthur M. Greene:
It would seem that there is some confusion, in the constants.html, between force and mass...
Beside the wrong unit which is fixed now I don't see any confusion.
Strictly speaking, kg is a unit of mass, Newton a unit of force. Weight is force, not mass: A gold brick floating in interstellar space is weightless but still massive. Pounds and kilograms can be equated, but only in some specified gravitational field (like at the surface of the earth, where we usually weigh things).
This is true for pounds-force and kilograms. Pounds-mass and kilograms could be equated in any context. Pound itself is ambigous.
So mass is the more fundamental quantity, since it does not depend on gravity for its value. In Imperial units (feet, pounds) the unit of mass is the slug: http://en.wikipedia.org/wiki/Slug_(mass). This is absent from the constants page.
Mmmh.. never heard of it though I read quite some English language aerospace engineering literature. However I'm using SI units. I think pounds-mass is more widely used as a imperial unit of mass.
I recall slug being used in amateur rocketry books 50 years ago or so. But SI units are definitely simpler.
Chuck
OK, since Charles opened the door: what about taking the bold, forward-looking step of not supporting "Imperial" units at all? (I say "good riddance.")
No, no! The point of providing these constants is so that users can easily convert everything to SI (or cgs) from the horrible units they are presented with by some third party. If we don't provide easy conversions, they'll stick to whatever random system of units they're stuck with. Anne
DG
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participants (10)
-
Anne Archibald -
Arthur M. Greene -
Charles R Harris -
David Goldsmith -
Florian Lindner -
John Hassler -
nicky van foreest -
Pauli Virtanen -
Robert Kern -
Warren Weckesser