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.


Big changes and getting lost in the system

So I mentioned that I’m now teaching physics at a very large high school in the mid-atlantic.  It’s the second day of the second week, and there are a few things that I need to put down in writing in a public place.

First off, I gave my students a math pre-test and a few of my students (all are 11th or 12th grade) could not plot points on a graph.  I’m not sure what the whole story is, but I know that all have passed algebra I and geometry.  Unfortunately I haven’t seen too many math classes so I’m not sure what to think.  My suspicion is a mix of grades not reflecting learning and math curriculum that doesn’t work with real data.  I’ll have to see more math classes and find out what I can build upon.

Second, I’m amazed at how hard it is to figure out who is responsible for certain students.  I’m already pining for the days when I couldn’t blame anyone for my physics students not being able to solve equations, because I was the only math teacher they have had!  I’ll say that much for small schools, you can’t really pass the buck when you’re 1/3 of both the math and science department.  Following up on three students involved 10 minutes of walking and visiting 4 different offices.

And yet, despite the size I have less freedom to try certain things.  I’m required to use points and percentages in Honors Physics, because the other two Honors Physics teachers don’t want to try something they heard of just a week before school starts.  Understood, but I fail to see how the grading system is any less of a variance than the vast differences in experience, labs and even homework.  But I suppose it’s mostly about the appearance of similarity, rather than the fact.

Ugh, that’s all sounding rather jaded.  No matter, these are just the things I have to take note of in the adjustment period.  I’ll figure out how to get them kids a learnin’!