We had lots of bumps in our acceleration graphs - I was rarely able to get any as smooth as those posted by Angie. I found that changing the time axis to 4 seconds (right click, graph options) smoothed out the bumps a tad, and took away some of the confusing noise at the end of the graph. I also changed from 3 to 4 batteries in the fans.
I was wondering why constant speed isn't a part of the acceleration graph portion. This is a clearly identified objective - An object that is moving at constant speed has zero acceleration, so the acceleration-time graph is a horizontal straight line at zero. I don't know if students are supposed to come to this conclusion based on the other graphs, or if it just got cut with time etc. I think that seeing this first would help students more readily interpret speeding up and slowing down graphs and reason through negative acceleration, especially as the trends on some acceleration graphs are much less obvious with with all of the bumps.
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I found that there were just bumps in the data like Wendy experienced. I first focused students' attention on the speed-time data and asked them what this data was showing them. We ended up identifying shorter periods of time to view and then looking at that same period of time on the acceleration-time graph. Some students didn't connect that the time period of .8 sec to 2.0 seconds on the speed-time graph related to the same period of time in the acceleration-time graph.
You're right, we ought to ask students about constant speed and what that means in terms of acceleration. I had a couple of good conversations about that with students today, and included it in the Idea Journal, but we should have that in the student sheets as well.
I reviewed this lesson the next day as a class demo (some groups had almost finished, some had barely started, depending on technology issues) and found that an effective way to do it - that also allowed us to pinpoint specific areas of the graph to look at different types of acceleration. We also looked at constant acceleration on that day.
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