Dear Joe, (01)
Jump to the end of the mail; there is my responsse. (02)
> ingvar_johansson wrote:
> >
> > Here comes the only passage where the SI brochure mentions 'torque'
> (pp.
> > 119-20):
> >
> > "In practice, with certain quantities, preference is given to the use
> of
> > certain special unit names, or combinations of unit names, to
> facilitate
> > the distinction between different quantities having the same dimension.
> > When using this freedom, one may recall the process by which the
> quantity
> > is defined. For example, the quantity torque may be thought of as the
> > cross product of force and distance, suggesting the unit newton metre,
> or
> > it may be thought of as energy per angle, suggesting the unit joule per
> > radian."
> >
> > Ingvar
>
> Excerpted from my copy of ISO/DIS 80000-1, "Quantities and units"
> -----------snip---------
> 3.2
> kind of quantity
> aspect common to mutually comparable quantities
>
> NOTES
>
> 1 — The division of the concept ‘quantity’ into several kinds is to some
> extent
> arbitrary.
> EXAMPLES
> a) The quantities diameter, circumference, and wavelength are generally
> considered to be quantities of the same kind, namely, of the kind of
> quantity
> called length.
> b) The quantities heat, kinetic energy, and potential energy, are
> generally
> considered to be quantities of the same kind, namely, of the kind of
> quantity
> called energy.
>
> 2 — Quantities of the same kind within a given system of quantities have
> the
> same quantity dimension. However, quantities of the same dimension are not
> necessarily of the same kind.
> EXAMPLE
> The quantities moment of force and energy are, by convention, not regarded
> as
> being of the same kind, although they have the same dimension. Similarly
> for
> heat capacity and entropy, as well as for number of entities, relative
> permeability, and mass fraction.
>
> 3 — In English, the terms for quantities in the left half of the table in
> 1.1,
> Note 1, are often used for the corresponding 'kinds of quantity'. In
> French, the
> term “nature” is only used in expressions such as “grandeurs de même
> nature” (in
> English, “quantities of the same kind”).
>
>
> -----snip------
>
>
> torque being "moment of force"
>
>
> n.b. - Units alone are not sufficient for determining "comparable
> quantities". (03)
I am as aware of the contents of VIM as of the SI brochure, and your
"n.b." makes exactly my point. What you might call "newton-meter as a unit
alone", I prefer to call "nominal newton-meter". However, note that only
some units can be called nominal units and tied to more than one
kind-of-quantity; many units are unambiguously tied only to one
kind-of-quantity. (04)
Ingvar (05)
>
> jbc
>
> --
> _______________________________
> Joseph B. Collins, Ph.D.
> Code 5583, Adv. Info. Tech.
> Naval Research Laboratory
> Washington, DC 20375
> (202) 404-7041
> (202) 767-1122 (fax)
> B34, R221C
> _______________________________
>
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> (06)
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