Posted in Constant Velocity Model

Building the Constant Velocity Model: “The Buggy Lab”

With modeling instruction, we begin each unit with a “Paradigm Lab” — a simple experiment used to build and develop the current physics model we will use to explain how our world works….or some of our world.

The Constant Velocity Model is the first unit (Science Reasoning is Unit 0), and is what a traditional physics class would call kinematics (well, part of kinematics). My set up and delivery is almost exactly like Kelly O’Shea’s.

This is our origin line that splits the room in half. First hour got to decide which way is positive and which is negative.


Using the “breadcrumb” method to mark positions at given time intervals.
Bigger breadcrumbs….post-it notes.

First hour went quite smooth, although every group started from the origin and went in the positive direction. I knew this wouldn’t make for a lively discussion, so during the five minute passing period, I whipped up some little slips to give to each group.

Each group got one of these slips of paper


What I hadn’t anticipated was the discussion these little slips would generate within the group before the whole class discussion. If we start negative, do we stay negative? And what does that mean about our velocity? Will we have a negative slope? And sometimes they realized their negative slope was in the wrong quadrant and they had graphed with negative time, and then admonished one another, “you can’t have a negative time!”

Those who crossed the origin had different questions; what in the world is the graph going to look like? Can we have a negative distance? Oh wait, its not distance….it’s position….so, will our graph cross one of the axes? Hmmm….

In the end the questions that came up (and were sometimes worked out) in their small groups came up again in the large group board meeting. And here we go, putting our heads together to figure out what all this meant and how so many different looking graphs can still explain the same type of motion. Score!

The Board Meeting for the Buggy Lab. This is their second BM, and they are starting to get the hang of it.

To wrap it up, we discussed the four models (representations) we got from this lab: diagrammatic (which we said was the sketch of our set-up), linguistic (our consensus definition of constant velocity), graphical (a nice linear position-time graph), and mathematical (xf = xi + vt).

A few notes about some favorite things I saw in my students during this lab:

  • My favorite “breadcrumb” was the brushes (the artist in the group)
  • One group (I later found out) laid several metersticks end-to-end and took video of their buggy. Then, to get accurate positions, they were able to pause the video as needed for their time intervals. Genius!

Do you have some thoughts about this activity? How do you teach your students about constant velocity?






I teach AP Physics at a public high school in Northwest Arkansas. I love what I do and want to be the best I can be, so my students can be the best they can be. I teach physics through a method called Modeling Instruction, and am a recent convert to standards based grading. This blog is my attempt to reflect on my own practices, share for anyone interested, and build a community of teacher-learners who want to grow together. Please comment and share your ideas!

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