[SciPy-User] Error in constants documentation?

David Goldsmith d.l.goldsmith@gmail....
Wed Apr 7 13:57:29 CDT 2010


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
>
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-- 
Mathematician: noun, someone who disavows certainty when their uncertainty
set is non-empty, even if that set has measure zero.
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