Re: supplementary S.I. units

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

Perhaps a definitive statement on the Radian can be found  in TPT vol. 31,
February 1993, pp 84-87.

This article was written by the AAPT Metric Education and SI Practices
Committee consisting of Gordon Aubrecht II, Anthony French, Mario Iona and
Daniel Welch.

The article, in addition to being interesting in its own right regarding the
Radian unit, stands as a quasi rebuttal to the introduction of the radian as
a base unit; I recommend its reading by all who have not read it.

Joel Rauber
 ----------
From: Joe Baughman
To: phys-l
Subject: Re: supplementary S.I. units
Date: Tuesday, September 22, 1998 12:40PM

At 10:37 AM 9/22/98 -0600, you wrote:
> I was intrigued by a note in this month's (September) issue of AJP (vol.
> 66, No. 9, page 814) which referred to a previous article from July last
> year (AJP, vol. 65, No. 7, pages 605-614) about making radians a real (base
> S.I.) unit rather than a supplementary unit.  I would like reaction from
> you brilliant people about the whole idea (I'm quite attracted to the
> notion that "radain units need never be spuriously inserted or deleted"),
> but also in particular to the comment in the note that "we usually forget
> that areas and length squared, or volumes and length cubed, are not the
> same thing."  I thought that was the whole reason we use meter cubed for
> the S.I. unit of volume instead of the liter.


Perhaps the distinction between area expressed in square units (ie, inches
squared) and "length squared" is because in math, I can find area or I can
take a single length and square it for some reason.

I envision that area would be a subset of any unit squared.  In other words
meters squared would be the set and it could express a "length squared" or
an expression of an "area".

My students get confused somethimes when they encounter the expressions
"square meters" (an area perhaps) and "meters squared" (a length that is
squared, perhaps).  It is a distinction I have never really gotten into in
class.

I too wonderously have Radians appear in a problem answer that appears to be
dimensionless.  I also am intrigued by the idea of using radians as a base
unit.  Maybe use of this "base" unit will clear up some confusions that
arise that rotational distance can be expressed in radians, revolutions,
degrees, gradients, etc., but when you work out calculations one must
usually express the unit in terms of radians.
>
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Joe Baughman                              e-mail:  joebau@blueridge.cc.nc.us
Science & Mathematics Instructor
Blue Ridge Community College           Telephone: (704)692-3572 x301
College Drive                                Fax: (704)692-2441
Flat Rock, NC  28731-9624

                 Web Server:  http://www.blueridge.cc.nc.us/
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