I normally share a lesson that I’ve already done with students, but I’m still tweaking this one and needing to write some thoughts down before my noggin turns back into soft tofu.

I bought these 14 pull-back friction toy cars (2 sets) for $30 at Costco. Amazon posts a video of how well these soft squeezable cars can stand up to toddler abuse.

**On your mark…**

- Each team of 3 students gets 1 car.
- How far the car moves forward depends on how far it gets pulled back — good lesson too for talking about potential and kinetic energy.
- The challenge is to get your team’s car to go a certain distance (reach finish line) without going over. This distance is not revealed until later.
- To predict for how much pull-back a car needs to go a certain distance, students “test drive” their cars for pull-backs of 2, 4, 6, and 8 inches.

**Get set…**

- Students are instructed to take measurements from the car’s front wheels.
- The blue tape marks the starting line. Front wheels line up at the front of the tape.

- The car is then pulled back a certain distance — here it’s 2 inches — and let go.

- When the car stops, the distance traveled is measured from front of wheels to front of blue tape. Looks about 13.2 inches here.

**Go!**

- Teams do 3 trial runs.
- Record and graph data on Desmos.

- Now teacher reveals and marks the distance each car needs to travel without going over. Say 15 inches.
- From graph, students extrapolate what the pull-back distance would need to be for car to move forward 15 inches. This distance is recorded and cannot be changed.
- Teams line up with their cars — one at a time — to pull back and let go!
- Winning car is one that reaches closest to finish line without front wheels going past it.

**Considerations**

- The cars roll best on bare floors. My classroom is carpeted, so we’ll need to do this outside.
- It’s fun that the cars actually vary in speed for same pull-back distance. The sports car (bottom left in above picture) is fastest.
- My kitchen floor is not big enough to test longer than 8-inch pull-backs, but the graph appears more parabolic.
- The data looks pretty awful, doesn’t it? Kinda? Maybe?

Ginny from Mathalicious was in the kitchen when I was playing with these toy cars. She shook her head and wondered if empty nest syndrome got the best of me. No matter. I think this will be a lot of fun. Will report back and post some pics.

[Updated 12/01/13]

Jon Orr @MrOrr_geek did this lesson with his Grade 9 students and wrote a great summary on his blog.

Here are a few pics from my class:

And a couple of video clips:

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