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9th Grade Math - Modeling through Geometry: Circumference of a Cup’s Roll

Clip 10/19: Modeling through Geometry: Lesson Part 2C


Molly McNinch’s students continue their group work with the [roll radius calculator](, as she challenges their thinking: “So, what does that mean about the comparison of the wide and narrow diameter?” Students consider different situations, and identify when it would help them to have a visual representation to evaluate their work. One group identifies similarity/regularity between the rolling cups and references a prior unit of study on similarity with triangles.

Teacher Commentary

I thought this lesson was great because I think a lot of them didn't think that they would get as far as they did. Their work inspired me to be like, "You guys are really capable, more capable than I think I anticipated, so we're going to start doing a little bit more. We're going to be doing a little bit extra because you guys can." It’s hard thing for me sometimes because I want them to do well and I want to help them, but at the same time it's like, "Okay, take it a step back." And seeing, "Oh, wow you guys really understood this."