[SciPy-User] Error in constants documentation?
Charles R Harris
Wed Apr 7 13:40:53 CDT 2010
On Wed, Apr 7, 2010 at 12:32 PM, David Goldsmith <email@example.com>wrote:
> On Wed, Apr 7, 2010 at 10:52 AM, Charles R Harris <
> firstname.lastname@example.org> wrote:
>> On Wed, Apr 7, 2010 at 11:02 AM, Florian Lindner <email@example.com>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.
> 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.
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