[SciPy-User] Error in constants documentation?

Robert Kern robert.kern@gmail....
Wed Apr 7 14:03:27 CDT 2010


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


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