[SciPy-User] Error in constants documentation?
Charles R Harris
charlesr.harris@gmail....
Wed Apr 7 12:52:36 CDT 2010
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
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