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I take no credit for this activity whatsoever. I saw the basic idea on Pinterest while looking for something else (for some reason I never pinned it), but I remembered the idea. In Geometry, students need to know cross-sections (G-GMD 4 - Identify the shapes of two-dimensional cross-sections of three-dimensional objects). To give students a better idea of cross-sections, I always explained it as taking a slice of a solid. The idea I found literally has students taking slices of shapes.
I gave each pair of students a tub of Play-Doh and some fishing line (about 18" long). Students formed shapes with Play-Doh and then sliced through them with the fishing line. The fishing line needs to be held taut when you slice or it won't work. It was suggested that you could use plastic knives, but the fishing line gives a much cleaner slice.
The activity worked well overall. Students understood the idea of cross-sections much better after physically making them. The only issue we had was that students' solids were not totally accurate, so their cross-sections were not 100% accurate either. I told students to try to visualize what it would look like if they had started with a perfect solid, and that was usually what students needed to realize what the cross-section should be.
I gave students a table to fill in for the notebook page. I found this idea when I did search for this activity, but I can't find it now to cite it. Students had to create a cylinder, rectangular prism, cone, and sphere, and slice them parallel to the base, perpendicular to the base, and then skewed to the base. This activity was simple, and pretty quick. (It took less than half the period.) I will definitely repeat it again next year.
Tip: Start with the cylinder. The Play-Doh is pretty much in a cylinder shape when you take it out of its container.
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