An Experiment in Process

This post outlines a recent lesson and activity I designed for my integrated chemistry/physics students. Fair warning: science ahead.


The Problem

I teach a class called Integrated Chemistry & Physics. It's meant to serve as an all-around physical science for high school students (they need one life science and one physical to earn a diploma). Being such, it's a light touch in a variety of topics in both physics and chemistry. It also provides a lot of opportunities for students to experience the ideas, particularly in physics.

I've run into an issue where lab activities designed for physics students often bog my group down in procedure and over-the-top data collection, which muddies the purpose of the lab. I wanted to simplify our usual acceleration lab to make it a little more accessible from a less science-oriented perspective.

The Plan

Simplification was the goal. The difficult thing about acceleration is that you need to measure distance and time accurately. Doing this without equipment becomes a challenge in teamwork, which was an added bonus for this activity. Rather than having one student use a timer, I decided to go with a metronome so everyone in the class could hear the correct interval. Students released a marble from the top of a slanted white board and traced the path of the marble as it rolled through an interval from the metronome.

I hadn't taught anything about acceleration yet, so I had the students hypothesize based on the following statement:

The distance a marble rolls will double if the time is doubled.

It provided an interesting discussion point as students argued over whether the marble rolled at a constant speed. Many didn't consider the fact that doubled meant every interval (0.25s to 0.5s is doubling the interval) or just a single block of time.

IMG_20150921_165017

The whiteboards had a nice record of the length of each trial. I know precision is just about out the window, but the generalities were helpful in building an understanding of what acceleration is. As they were taking data, there were exclamations of, "I can't keep up! It moves too fast!" Having the kinesthetic experience through manual tracking is something that is lost when tech is used to get more precision.

The Results

Because this was done manually, the data were all over the place. Depending on how well the group worked, some had negative accelerations at the top of the board and very, very high accelerations at the bottom. I'm a fan of error in data because it reinforces the fact that being careful in the lab is very important. I had each group report their average distance rolled for each interval and I was able to graph the class data as position vs time and speed vs time to highlight the difference in shape for acceleration between the two.

PTgraph

STgraph

Further Discussion

The nice thing about this lab is that it had components of very close teamwork, kinesthetic experiences, an achievable task, and great error for analysis. While we were discussing group results, students were noticing that their results varied widely between each group. So, I took the class data and animated how the graph changed as more and more data are added to the set.

Students immediately saw that the graph approached the correct shape as more data were added. I'm hoping this starts to end the question, "How many trials do we need?" in future experiments.

Next time I run this experiment, I'll probably use ticker tape cars to remove the variability in data. I liked that they had to physically move the pen faster as the marble accelerated, but it caused a lot of issues in data analysis the next day and may have even introduced some misconceptions about acceleration.

What suggestions would you have? What changes could keep some of the kinesthetic experiences and simplicity in structure but improve on the task as a whole?

<a href="https://docs.google.com/document/d/1J4xTRuEUVPRnp8IjEGTrYs55Wm1N1-j6X8DqtkOVHZg/edit"Here's the document for copying.

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