Re: [Phys-l] Independent Variables

["John Clement" <clement@hal-pc.org>]

This is a very deep problem that reveals the level of thinking of students.
The lower level thinkers have extreme difficulty with it.

Have the rule that you usually plot the independent variable on the
horizontal axis is not all that bad.  It lines up with the ideas in math.

But they also have problems with commands such as "plot a vs b".  The fact
that a is usually the dependent variable, but is always plotted on the
vertical axis goes against the x,y semantic ordering.  Indeed the dependent
variable is normally on the left in graphs, equations, and in the plot
command, but is on the right in tables, and ordered pairs.  They need to
have this drawn to their attention.

And there is the problem that they can not parse a sentence to decide which
variable is independent and which dependent.  To a certain extent this is a
reading problem.  They need to be able to pick out the subject, verb, and
direct object.  Usually the dependent variable is the direct object and the
independent is in a clause, but not always.

This also is a problem that they do not understand the concept of variable.
They use the word, but it is easy to tell them to plot things where they
have not grasped the idea of variables.  Again this correlates strongly with
the Piagetian level of thinking, which needs to be raised.  Most
conventional teaching does little to help them.  The Karplus scientific
learning cycle helps a lot here.  Also there are interventions such as
Thinking Science that are designed to also raise the level of thinking.

One does not have to actually get into cause and effect, but they do have to
think in terms of input/output.  You change one thing and then find out the
result.  Cause and effect is a very useful handle here.

The best way of clarifying it is to have them frequently identify the
independent and dependent variables.  This is what Modeling does in all labs
as the purpose.  You could try to use the word responding variable rather
than dependent, but switching words will not really help if the problem is a
low level of thinking.

John M. Clement
Houston, TX
> On Oct 30, 2006, at 8:47 PM, thecraftyphantom@australia.edu wrote:
>
> > I was discussing independent and dependent variables with my physics
> > students in a recent class.  No matter how I approached the subject a
> > number of them asked questions that showed they were having difficulty
> > with
> > identifying the independent and dependent variable in a number of
> > cases.
> >
> > Have others struck this difficulty?  If so, what approaches have you
> > used
> > to clarify this issue for students?
>
> 1) In physics, unlike in mathematics, the issue becomes important when
> laboratory data are plotted. Why do you need adjectives, such as
> "dependent"  or "independent?"  Our variables already have names, such
> as time, distance, voltage, etc.
>
> 2) At a deeper level it might become the cause-and-effect issue. Why do
> you really want to deal with this issue?
>
> Ludwik Kowalski
> Let the perfect not be the enemy of the good.
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