[SciPy-User] Error in constants documentation?

Florian Lindner mailinglists@xgm...
Wed Apr 7 12:02:49 CDT 2010


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.

Regards,

Florian

> 
> Regards,
> 
> AMG
> 
> Warren Weckesser wrote:
> > Florian Lindner wrote:
> >> Hello,
> >>
> >> http://docs.scipy.org/doc/scipy-0.7.x/reference/constants.html chapter Force says:
> >>
> >> dyn 	one dyne in watts
> >> lbf 	one pound force in watts
> >> kgf 	one kilogram force in watts
> >>
> >> doesn't the watts actually have to newtons as the unit of force?
> >>
> >>   
> > 
> > There is a ticket with the same question here:
> >     http://projects.scipy.org/scipy/ticket/1001
> > 
> > 
> > Warren
> > 
> >> Regards,
> >>
> >> Florian
> >> _______________________________________________
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> >> SciPy-User@scipy.org
> >> http://mail.scipy.org/mailman/listinfo/scipy-user
> >>   
> > 
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> 
> 


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