The growing pains of collecting data by using the stopper lab for the circular motion unit is well known to a number of teachers. In the modeling workshop I attended at ASU, everyone was forewarned of how difficult it was to collect good data, and sure enough, it was messy. So I have been on the lookout for different approaches to introduce the circular motion (central forces) unit.

I was really happy when I came across Casey Rutherford’s great idea of collecting data by using an accelerometer (Labquest 2s) strapped to a spinning chair. Check out his blog post. He also has great ideas on how to introduce the topic, which I have borrowed as well. So I tried using the chair to collect data, but I was having trouble getting the smooth spinning motion. Then I decided to pay a quick visit to the art room, and there I found out I could use a low friction sculpting turntable instead of a chair as my set up. For measuring the acceleration, I used Vernier’s Wireless Dynamic Sensor System, and it worked better than I expected. Here is the whole thing doing its job:

To measure velocity, some students timed the period of rotation, while others used a photogate. I test drove this lab before trying it with the students, so here is the data I collected. I changed the velocity and measured its effect on the acceleration:

Then I squared the velocity for linearization. Then students were able to derive the equation for centripetal acceleration, with the slope being the inverse of the radius. The results were great.

I’m really satisfied with this new approach to the circular motion lab, and I no longer have to tell students that the data may or may not work. I am definitely using this method again next year.