*Physics 11* – Today we finally debriefed the lab results. There wasn’t a lot to say at this point because we had spent so much time talking about things just to get here. I really wish I could see how other modellers handle this kind of thing, I wonder what their whiteboard meetings look like?

A few things I would do next year, if I do this again:

- Force all groups to graph F vs a. While we agreed that a vs F made more sense with acceleration being the input, the analysis for realizing a general model from this is not obvious. By graphing F vs a, it’s easier to see that the slope is the system mass
- Have each group explicitly write down their system mass in kg while collecting data.
- Have a clearer discussion on how Fg = Fnet. I mentioned it, but I don’t think it resonated with the students.

**Would I do this lab again?**

There are three major problems with this lab. First, it took a heck of a long time. Second, not all the kids seemed to get the big picture. They got some data, calculated numbers that Mr. Smith told them to, and graphed them like Mr. Smith told them to. Some kids don’t fully appreciate the thought they put into their work. When they ask me questions like “what do I graph?”, I’ll answer with things like “well, what relationship are you trying to find? What should you graph? What should your independent variable be?”

My last statement above highlights the third problem. If they kids graph a vs F, which makes sense, then there is no obvious physical explanation for the slope. I have to explicitly tell them to change their equation to a =… (why?) or to purposely graph F vs a.

On the positive side, 2 of my 3 classes categorically thought the lab was good and recommended for next year’s class to do it. Several kids did have a solid A ha! moment, which is always good. Others said that playing with the video and analyzing the data made them appreciate how forces have a direct affect on acceleration.

I wonder if a more qualitative lab could replace this one? Something like what Josh Gates wrote about in the Physics Teacher (2014). I currently can not do exactly what he does because I don’t have the sensors, but it could be something to aim for.

Gates, J. (2014). Experimentally Building a Qualitative Understanding of Newton’s Second Law.

*The Physics Teacher*,

*52*(9), 542–545.

http://doi.org/10.1119/1.4902198

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