Pushing on Experimental Practice

Two weeks in, and I have something I have deemed worth blogging about. In both my Honors and General Physics classes, I have been pushing hard on good experimental practice. For now, this breaks down into thinking about uncertainty and getting rid of sloppiness.

In both General and Honors, we have now completed the first Physics By Inquiry lab where students are given a ball bearing, track and told to create uniform motion. This year I tried to grease the skids a bit by asking for definitions of speed before we started. I didn’t validate any one, but I slowed down my handwriting when a definition included what should be measured (distance and time). That seems to have reduced the time to get metersticks and stopwatches into action.

In both classes, I used this lab to discuss the uncertainty in their time measurements. It was rough, but I had them starting and stopping the timers to get an estimate of their reaction time. That’s a huge logical leap and completely inaccurate, but it’s a good start on realizing that what the clock says is not an objective truth.

In the Honors class, we did a measurement lab to establish the reasoning behind significant figures. The students were given a piece of string, rulers were banned, and they had to measure their table. We discuss how they must estimate the last portion of the string length, usually giving us an uncertainty of +/- 0.1 strings. Then they calculate surface area three times (smallest possible, normal, and largest possible) to find the uncertainty in the surface area, which is usually 1 string. If you do some of the calculations yourself, you can probably figure out how that gets you the sig fig rules.

Finally, I also used these labs to push on being good experimenters. Almost like a perfect plant, one student said “it’s not like this lab actually matters.” Which allowed me to launch into a diatribe about how in this class we will be learning from the labs, rather than doing labs to confirm results. I don’t think that has sunk in yet.

The things that I pushed on for good experimentation were parallax (reading the meter stick straight on), not trying to push a ball and start a timer at the same time, allowing people who time to anticipate when the ball reaches their mark, and using paper for fine height adjustment of one end of the track.

I apologize for the low quality of writing in this post, but I had to get this down before I move on to bigger and better things. Depending on how this year goes, I may push more or less on good measurement at the beginning of next year.


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