Re: [Phys-l] Independent Variables

[Hugh Haskell <hhaskell@mindspring.com>]

At 12:47  +1100 10/31/06, 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? 
It depends on just what they were hung up on--the idea of the 
independent variable as the one you adjust and the dependent one as 
the one you measure, or the idea that the independent variable goes 
on the horizontal axis and the dependent one goes on the vertical 
axis.

The first is pretty obvious, it seems to me, and the other is 
arbitrary. In fact, I don't see much value in spending time on that 
aspect, because students want to have rules that they can follow 
without having to think about it (that's why sig. figs. is something 
that too much time is spent on), and dependent/independent variables 
is one of those arbitrary rules that students want, but then get hung 
up on because there is no underlying logic to them--or at least not 
much.

I purposely do a couple of lab exercises where I have them plot the 
dependent variable on the x-axis and the independent on on the 
y-axis, because that is the way I want the slope of the line to come 
out. That bothers some students because they have this hang-up about 
an arbitrary rule,and I am consciously trying to break it down, by 
showing them that it *is* arbitrary, and that there are all sorts of 
very logical reasons why one would put the dependent variable on the 
horizontal axis.

The students have to think about how the graph of their results makes 
sense, and if they are looking for a linear graph and need to measure 
the slope, it makes a whole lot more sense to put the quantity that 
will become the denominator in the calculation of the slope on the 
horizontal axis.

If they can figure out what is best by thinking about what they are 
doing, rather than remembering arbitrary rules, they will be a whole 
lot better off.

Hugh
--

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

(919) 467-7610

When you are arguing with a stupid person, it is a good idea to make sure that
person isn't doing the same thing.
					Anonymous