What happens to the surface area of a cylinder when you double the height? I posed this question to my students as a Commit and Toss formative assessment last week because I wanted to see if they would realize that while the volume has doubled, the surface area has not.

sa-cylinder-with-double-height-commit-toss

As we discussed the question (which is the final stage of a Commit and Toss formative assessment), I was really pleased that the response I got universally was that the volume doubled but the surface area did not. They talked about the fact that the area of the bases had not doubled, only the area of the “side” had. (This was a definite win after the previous Commit and Toss activity – see my last post).

Since things went well, I followed up with the question of how things would change if the radius was doubled. No one was quite sure, so we took some time to explore the question. It was a good day. It’s always a good day when students want to know more.

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