Document the Positive #2

I made a promise to myself that I would document positive things this entire week.  Today I’m going to focus on experimental method.

At the beginning of the year, I changed my approach to uncertainty and measurement.  I just wish that I had continued the push well into the year.

In the past, I’ve done this great lab on measurement that I got from my cooperating teacher during my student teaching.  The students are asked to measure the length and width of a lab table using only a piece of string.  The point is that their measurement has a large uncertainty due to the quality of their tools.  Then they calculate area to see how uncertainty in measurements propagates.

In previous years, this quickly turned into the rules for significant figures.  During the lab, I made them keep writing all measurements as:

3.4 +/- 0.1 strings

But in honors physics I jumped to just using significant figures too quickly.  I assumed that my honors students were higher skilled than my general physics students (whoops!).

The major benefit was that uncertainty in measurements wasn’t just “our result is wrong” or the useless “human error.”   We changed our language so that uncertainty was in “human hands using a cell phone timer” or “normal eyesight and a meterstick.”   Therefore, it was easier (although still difficult) for students to see slightly different numerical results as equivalent.

So what I’d like to do next year – to push the uncertainty of measurements throughout the year, is to require the plus/minus on every lab.

I’m also thinking it would be nice to have a measurement problem on quizzes/tests.  Something where I’ve taken measurements, and the students need to apply their calculations and provide a prediction along with uncertainty.  Well, maybe that might be a bit much.

Right, so that’s something I’m proud of.  It set me a solid week behind the other physics teachers, starting a slow drift resulting in my being 1-2 units behind the other teachers at the end of 3rd quarter.  I think the ability to compare real measurements is worth the time.


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