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Re: [Phys-l] Independent Variables



Ignoring the 'Psycho/Edu babble', I would go along with Hugh and Ludwik that a physics course should pretty much avoid the nomenclature. In the lab we tend to have a controlled variable and a measured variable. In a free-fall experiment, we might control the height and measure the time. If however, we call these the independent and dependent variables, there will be confusion when we choose to plot the height versus the time--ultimately wanting to know how the distance an object falls evolves with time.

What is graphed on the x-axis and what on the y depends much more on what information we really want and how much theory we might have going into the experiment. As mentioned, sometimes we 'know' what we want the slope to tell us (say resistance in an Ohm's law experiment and therefore will plot the measured current on the x-axis and the controlled voltage on the y).

'Luckily ;-)' I find my gen-ed students don't remember (or know) enough math to get hung-up on this, and my science majors are willing to 'go with the flow' and don't make much of a fuss either. Of course the technology helps--using Excel to do our plotting means that a 'backwards' graph can be fixed in a matter of seconds!

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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