Lesson 2: Cross-sections of Solids

### Hands on introduction to cross-sections:

Students should complete a hands-on activity with toilet paper tubes. The tubes can be cut to show the cross sections.
Toilet Paper Tube - This activity should be used to illustrate the different results students will get with the toilet tube before working on SketchUp.

SketchUp Activity:
Goal: Identify solids through an investigation of cross sections. [7.G.3 G.GMD.4]
Learning Objective: Students should begin to see a difference between polyhedra (prisms and pyramids) with polygonal faces and non-polyhedral (cones, cylinders, spheres).

Demonstration: Video: no audio recorded

Task: Create a variety of solids (or use the files prepared in Lesson 1) and drag a cross section through each solid. Discussion questions to ask include:
1. Name a figure and location of the plane where the cross section slice is constant (same shape and size) as you move the section tool through the figure.
2. Name a figure and location of the plane where the cross section slice is a polygon but the polygon shrinks/grows as you move through the figure.
3. Name a shape where the cross section slice is not a polygon as you move through the figure. Where is the plane located?
4. Name a figure where the slice is curved (parabolic) and note the location of the plane.

Follow-up Question:
Can you classify or categorize the solids by using distinct properties of the cross section slices?

Teacher Notes and files:
Materials: Prepared SketchUp file (Use your files from Activity #1), discussion questions, physical models
Vocabulary: A polyhedron (plural polyhedra or polyhedrons) is a geometric solid in three dimensions with flat faces and straight edges.http://en.wikipedia.org/wiki/Polyhedron

June 2014 - Updated