Re: [Phys-l] Independent Variables

["Bob LaMontagne" <rlamont@postoffice.providence.edu>]

I agree with Ludwik - I would simply avoid use of the words dependent and
independent. Yesterday, I did a conservation of energy lab with the Intro
Physics students. We drop a ball into a bucket of sand and create craters.
If a fixed percentage of the potential energy of the ball becomes potential
energy of the lifted sand, the fourth power of the crater diameter should be
proportional to the height through which the ball fell. The students prepare
a graph of the height versus the 4th power of the diameter of the crater and
it turns out to be surprisingly linear - and in a log-log plot the slope is
4. However, both the height of the ball and the diameter of the crater are
measured values. It really isn't appropriate to consider one as dependent
and the other as independent. They just are what they are - measured
quantities.

Bob at PC

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of Ludwik Kowalski
> Sent: Monday, October 30, 2006 9:39 PM
> To: thecraftyphantom@australia.edu; Forum for Physics Educators
> Subject: Re: [Phys-l] Independent Variables
>
> 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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