Re: [Phys-l] explanatory and response variables (was calibration )

[John Denker <jsd@av8n.com>]

On 08/09/2007 09:37 AM, Spagna Jr., George wrote:

>  I tell my
> students that the "independent variable" is the one they control, the
> "dependent variable" is the one they measure as a result of setting the
> independent variable.

There are some cases where that makes sense, but there are also innumerable
cases where it does not make sense.

On 08/09/2007 02:09 PM, Barbara Bay wrote:

> > when you are deciding on what to call things, you might want to check
> > through the math standards for different states for the commonly used
> > terms. 

Excellent advice!

For years, I have been keeping track of the California standards 
in physics and chemistry ... but until just now I wasn't keeping
track of the math standards.  So I learned a couple of useful
things today, thanks to phys-l contributors.

What I know of the California standards comes from here:
  http://www.cde.ca.gov/ta/tg/sr/css05rtq.asp
which points to:
  http://www.cde.ca.gov/ta/tg/sr/documents/rtqgeom.pdf
  http://www.cde.ca.gov/ta/tg/sr/documents/rtqalg1.pdf
  http://www.cde.ca.gov/ta/tg/sr/documents/rtqalg2.pdf
  http://www.cde.ca.gov/ta/tg/sr/documents/rtqchem.pdf
  http://www.cde.ca.gov/ta/tg/sr/documents/rtqphysics.pdf


> >  The State of California agrees with Dr. George
> > Spagna, Jr. 

No, not really, not so far as I can tell from aforementioned
California documents.

> > In the high school Math standards, the terms "dependent
> > variable", "independent variable", "x-axis" and "y-axis" are used.

Dependent and independent variables are mentioned in item 17.0 of
the algebra I standard.  They are not mentioned in the other four
standards (algebra II, geometry, chemistry, and physics).

They are used in the context of mathematical functions, and appear
to be intimately related to the idea of domain and range.  There
does not appear to be the slightest requirement to associate them
with physics experiments or with whether a variable is "controlled" 
or not.

    Tangential remark, FWIW: the terms "horizontal axis" and "vertical 
    axis" are also used in the algebra I standard.


On 08/08/2007 11:35 PM, Ken Fox wrote:

> (I am not convinced that the H-R diagram is designed to be a functional plot
> and thus does not follow any of the rules we have been trying to agree
> upon.)

1) What's a "functional plot"?  In real estate, they talk about multi-functional
plots, but I've never heard that term used in the context of physics.  What
do we call it if it's not a functional plot?  A dysfunctional plot??? :-)
Why can't I just make plots, without distinguishing the "functional" ones
from the others?

2) Obviously we don't /control/ the luminosity and we don't /control/
the color of stars.  But that does not hinder me from plotting luminosity 
versus color.  There is not even the slightest hindrance.
  2a) Design of the experiment is important.
  2b) Design of the data presentation is important.
  2c) Items (2a) and (2b) are not the same thing!  The are nowhere
   near being the same thing.


In the context of mathematical functions, I understand abscissa and
ordinate.  I understand domain and range.  If you want to apply the terms 
independent and dependent, that's harmless /in this narrow context/.

However, if we transplant the terms from math to physics, and then
overload them with the idea that independent variables are "controlled"
during the experiment ... that's just crazy.  Maybe some experiments
are done that way, but most of them aren't.  There's no reason why
they should be done that way, and many reasons why they can't be done 
that way.

Let's not read into the standards more than is actually there.  I 
have not seen any state standard that even pretends or attempts to 
require experiments to be done that way ... which is good, because
any such attempt would be absurd.  There are enough absurdities in
the standards already.