Buggy lab mid-teaching analysis
After we completed the Marshmallow Challenge, we jumped right into the Buggy Lab, which introduces students to small battery powered buggies. I’m going to try to give the play by play here and raise a few questions about my own practice.
I started by turning on the buggy and letting it roll across the table, and asked “What do you notice?” (Thanks Brian for teaching me about the power of this question).
Students quickly notices all sort fo things, from “it moves” to “it lights up” to the “the wheels are rotating at a constant rate.”
I then push my students to tell me what they could measure, and the most common response is “speed”, and so I say how do you measure speed, which they usually unpack as measuring a distance and the time it takes to travel that. After we talk about how to measure the distance and time, I usually set them loose.
Almost all of my students glom onto the following basic experiment—measure a fixed distance (say a meter) then release the cart and measure the time it takes the cart to travel that distance, and repeat this 3 times, then average, and here a few might call it a day.
So I go around and ask them if discovering the speed of the buggy is really all that exciting—would they want to tell their parents that’s what they learned on the very first day of school? They say no, and we talk about digging deeper to find a relationship.
I ask my students what sort of things have relationships, and we work our way through people (eg father-daughter), and then quantities, like circumference and diameter). I ask them how you know those things have a relationship, and they all said that if you graph circumference vs diameter, you’d see some sort of line. So we then decided our ultimate goal should be to determine the relationship between the distance traveled by the cart and time.
We talk about why they repeat trials—most of them seem to have think that is just something you do to avoid “human error.” So in the spirit of Brian Frank, I resist my temptation to simply ban the word human error completely and ask them what they mean by that—that gets them to tell me something about how it’s hard to press the stopwatch at exactly the same time as when you drop the car on the ground, so the measured time will always be different form the actual time, and averaging seems to account for sometimes you might be a little slow, and other times a little fast in pressing the buttons.
My students see pretty quickly that this doesn’t really allow one to determine the relationship between distance and time, and that what they really need to do is have the car travel a number of different distances and record the times it take so that you have data for a wide range of distances.
To get to this point, it’s taken most groups about 30 minutes. And we’ve still got lots of good points left for discussion for when groups come together, like whether we should be plotting distance or time on the horizontal, and what to do when one group measures in inches, one group measures in floor tiles, and one group measure in cm. When I ask the question “which cart is fastest?”, I am hoping they will suddenly see the need to standardization in terms of how we graph and measure in a more visceral way than if I had just told them what to do.
Now here’s where I have some questions.
Last night at the Global Physics Department, Kelly O’Shea and I got to chatting about the lab, and she was telling me that while everyone is together, she pushes them a bit further toward agreeing on how they will proceed. She draws up a graph with labeled axes and a data table on the board, and then everyone leaves to make measurements knowing they will be plotting distance in cm vs time in seconds. This is a huge time saver, for sure, and in many ways it saves kids a lot of frustration of having to go back and re-measure/re-graph things once they realize they did something wrong.
Ultimately, this is the age old question of just how much guidance we should provide—more and more I’m feeling I should give more guidance than I did yesterday, if for no other reason it will save me from having to have 6 individual conversations with each lab group and feel like I’m trying to push them to mold their experiment toward my thinking, rather than having them set up some sort of common foundation and then exploring on their own from there.
I would love any thoughts you may have on my approach, and suggestions for finding that balance between open-endedness that allows students to go down blind alleys that can lead to frustration, and guidance that keeps them on the path, but may prevent them from fully seeing the nuance of what they are doing.