# [SciPy-User] Error in constants documentation?

David Goldsmith d.l.goldsmith@gmail....
Wed Apr 7 13:32:03 CDT 2010

```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
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