Monday, April 25, 2011

For Your Reading Pleasure...

The Physics Teacher just published an article of mine:

A Teachable Moment Uncovered by Video Analysis

It's a whirlwind ride through a simple kinematics lab (rolling a ball down a flat track, modeling its outgoing speed as a function of its incoming speed).  As it's the first lab, I want to give a good introduction to exactly what I mean by "error analysis," and it's not some weak hand-waving about 'human error' (go ahead and remove that from your vocabulary!  It means nothing - that's why you always have to explain what you mean by it - and implies that non-human measurements have no uncertainty, which is flat wrong).

I have them analyze an example video of this bouncing action.  The constant initial speed assumption is good, the instantaneous bounce assumption's pretty good, but the constant final speed assumption is easily belied by the position vs. time graph.  Why?  Friction!  That sliding sounds that some of them heard (and ignored, because there wasn't a quick and easy explanation for it) was the ball changing rotation direction, at the expense of some speed.  Now we know that the calculated speeds (from the time interval from impact to some other point) were uniformly fast.  That's a good piece of error analysis for high school.

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