Cross Section Lesson
Objectives:
1) Students will develop spatial-visualization skills through creating cross
sections of solids.
2) Students will sketch solids that contain given cross sections.
Term(s):
Cross Section is defined as the geometric figure formed when a solid is cut by a
plane.
Materials:
Play dough, plastic knives, hallow solids for molds (optional)
Lesson Outline:
• Launch
Ask students “What is a cross section?”, place a good definition of this on the board.
Demonstrate cuts that would form a plane and cuts that would not form a single plane.
The solids they are to work with can be formed by hand with play dough or using solids
as molds.
• Explore
Students are to complete the Cross Sections of Three-Dimensional Shapes Handout.
• Summarize
Ask students: “What solids could be used to create this triangle shaped cross section?”
“What cross section is formed when a cut is parallel to the base of the solid?”
An extension relating area to volume is Cavalieri’s Principle which states:
Consider two geometric solids and a plane. If every plane parallel to this plane that
intersects one of the solids also intersects the other so that the resulting cross sections
have the same area, then the two solids have the same volume.
Recipe for Play Dough
1 C. flour 2 T. salad oil
½ C. salt 1 C. water
2 tsp. cream of tartar 2 drops of food coloring
Add food coloring to water. Mix all ingredients together and bring to a boil. Turn onto
wax paper and knead. Store covered in refrigerator. A single recipe makes
approximately 27 in3, it is recommended the recipe be doubled for a class of 24 students.
Source: Navigating through Geometry in Grades 6-8
Lesson available at http://www.mnstate.edu/harms/Lessons/LessonsActivities.htm
Electronic manipulative at http://matti.usu.edu/nlvm/nav/vlibrary.html
