# Day 14: First Counting Circle

*College-Prep:* Today we wrapped up the spring lab. Each group put their graphs on a whiteboard and we compared/contrasted graphs. We got at the notion that the slope represented the “Stiffness Factor” of the spring. To illustrate the linear nature of the spring force, we made a Counting Circle.

Considering a 0.22 N/cm spring, we stood in a circle around the room and counted off the amount of force that would be needed to get the spring to stretch every centimeter — 0.22 N, 0.44 N, 0.66 N, etc. It wasn’t easy for everyone. (In the essence of time, I use 0.25 N/cm for my other 2 classes.) Then I asked random kids what their force was (easy for them to recall) and then what their stretch was (Uh, oh. You want a calculator? How could you figure out without one? How many different ways can you solve the problem?)

I could see doing this for things like the speed of a tossed projectile every second. Or even the height of the projectile every second (TRICKY!).

I learned about Counting Circles from Sadie Estrella, a rock star math teacher from Hawaii. You can read more about her work on Counting Circles:

- TMC13 Presentation on Counting Circles
- The Blame Game (a post about why Sadie does Counting Circles).

##BFPM ##CountingCircle

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