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



Hugh you are right, of course, and this is a classic example of the
difficulty of having a fixed rule. Which does depend on the other, time or
distance. It is easier to control the distance for sure and thus I implore
the student to think and discuss. I am of the school that looks for
functional and physical dependency. From the functional point of view, time
must be the independent variable. One cannot have 2 distances at the same
time.

So why worry about dependent/independent? I guess that I like to think in
terms of cause and effect, but the list has already made that a spurious
point of view. If I am to plot a N2 lab, I will put "a" on the ordinate and
either "F" or "m" on the absissa. Then I feel good about a developing a
functional and physical relationship, thinking that acceleration is the
result of what force on which mass. What to do with Ohm's Law? I like I vs
V.

I think I should have avoided my lame effort to marvel light heartedly at
how little agreement there is about this issue, and how little progress has
been made. Sarcasm does not email well. Future generations are safe, as I am
now retired, but still interested.

Ken Fox


On 8/8/07, Hugh Haskell <hhaskell@mindspring.com> wrote:

At 23:35 -0400 8/8/07, Ken Fox wrote:

Egad! I had no idea of how confused my students must have been as I
blithely
discussed that the independent variable should be on the x or horizontal
axis and the dependent on the y or vertical axis.

So what do you tell your students when they do an experiment where
they put photogates at fixed positions along, say, a tilted air
track, and measure the times that the glider passes them. Have they
not done an experiment where the independent variable is distance and
the dependent variable is time? And if so what do you tell them when
they plot time on the y-axis and distance on the horizontal, and find
that the velocity measurements come out in sec/m?

Why worry about dependent and independent at all? If they are not in
a position to figure out for themselves what the optimum way to plot
a graph is, then just tell them put whichever variable will be the
numerator of slope measurements on the y-axis and the other one on
the x-axis. And when they complain that their chemistry teacher told
them to worry about dependent and independent variables, just tell
them that you are freeing them from that restriction. All they have
to do now is to think about what they are going to do and do the
thing that makes most sense. That means about a million arbitrary
rules that they no longer have to worry about.

Then you can take up a collection among your faculty colleagues to
provide help for the chemistry teacher who just had a nervous
breakdown, because now his most righteous rules
(dependent/independent variables and significant figures--see earlier
posts) have both been violated.

Hugh
--

************************************************************
Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

(919) 467-7610

Hard work often pays off after time. But Laziness always pays off now.

February tagline on 2007 Demotivator's Calendar
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