[SciPy-User] Error in constants documentation?
Thu Apr 8 13:38:09 CDT 2010
On 7 April 2010 14:32, David Goldsmith <firstname.lastname@example.org> wrote:
> On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris
> <email@example.com> wrote:
>> On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <firstname.lastname@example.org>
>>> 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.
> 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
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