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

[Jack Uretsky <jlu@hep.anl.gov>]

On Wed, 8 Aug 2007, Michael Edmiston wrote:
Hi all-
	I reviewed the answers to this up through the middle of 8/9.  It 
amazed me how many responses were self-congratulatory messages that seemed 
to miss what I must insist is the essential point.  I will forward the 3 
or four exceptions that I identified.
	The point:  In answer to the question, what makes sense as a 
description of axes for a graph?  Find out what you can agree with with 
your students in THIIS class as an acceptable description.
	Moral:  teach to the actual student, not to the caricature of a 
student that you carry around in your head.
					Regards,
					Jack
follow-ups coming




> John's comments about independent and dependent variables reminded me of
> some questions I would like to pose to the group.
>
> (1) What should we call the axes of a 2-dimensional graph (in general)?
>
> horizontal and vertical
> x and y
> independent and dependent
>
> I am amazed how many students don't know horizontal and vertical, but
> probably they are more familiar with that than with independent and
> dependent.
>
> x and y are usually understood, and that is usually what spreadsheets call
> them, but it seems odd to call them x and y when we are not plotting y as a
> function of x, but perhaps plotting current as a function of voltage.
>
> If we are plotting current as a function of voltage, is it just best to get
> over my hangup and tell the students that voltage is on the x-axis and
> current is on the y-axis?
>
> (2) If I tell students to "plot current versus voltage," or my preferred way
> is to say "plot current as a function of voltage," many will ask which do I
> mean is the x-axis, etc.  Those who don't ask seem to have a 50/50 chance of
> doing it backwards.
>
> Am I old fashioned?   If I use the phrase "plot current as a function of
> voltage" would most (all?) practicing physicists understand I am askling for
> current on y and voltage on x?  If so, why aren't students learning this?
> If not, what terminology should I be using if I want to use what's being
> practiced?
>
> (3) What alternative words do we have for a 3-D coordinate system?  For a
> standard right-hand system I generally say the x-axis runs left to right
> (right positive), the y-axis runs backward to forward (forward positive),
> and the z-axis runs bottom to top (top positive).
>
> I know axes can point anyway you want them to point, but do most people
> generally visualize it as I said?  In textbooks we often see x to the right,
> y pointing up, and z pointing backwards.  To me, that does not fit with
> other practical things such as numerically-controlled milling machines, etc.
>
> Bottom line... if there is some standard language that is different than
> what I visualize, I have missed it, and so have many years of students.  If
> there isn't any standard language, or if the standard is not being taught,
> no wonder students are confused.
>
>
> Michael D. Edmiston, Ph.D.
> Professor of Chemistry and Physics
> Bluffton University
> 1 University Drive
> Bluffton, OH 45817
> 419.358.3270
> edmiston@bluffton.edu
>
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