Math Background

Lesson: Identifying and Classifying Solid Figures
Developing the Concept

In the first lesson, students learned to recognize and name solid figures. In this lesson, students will explore the parts that make up solid figures.

Materials: one rectangular prism, cube, sphere, cone, cylinder, and pyramid for each group of students

Preparation: Distribute solid figures to groups of students.

Prerequisite Skills and Background: Students should be able to recognize and name solid figures.

  • Ask:Which solid figures have faces that are polygons? (rectangular prism, cube, and pyramid)
  • Say:Put the other solid figures aside for now.
  • Ask:Which solid figure has faces that are rectangles? (rectangular prism)
  • Say:Count the number of faces a rectangular prism has. Mark an X on each face as you count.
  • Copy this table on the board as students are working. table
  • Ask:How many faces does a rectangular prism have? (6)
    Record 6 on the table.
  • Say:The line segment where two faces meet is an edge. Count the number of edges a rectangular prism has. Mark an X on each edge as you count.
  • Ask:How many edges does a rectangular prism have? (12)
    Record 12 on the table.
  • Say:The point where edges meet is a vertex. Count the number of vertices a rectangular prism has. Mark an X on each vertex as you count.
  • Ask:How many vertices does a rectangular prism have? (8)
    Record 8 on the table.
  • Have students find the number of faces, edges, and vertices of a cube and a pyramid. Record the answers in the table.
    table
  • Ask:Why do you think that a rectangular prism and a cube have the same number of faces, edges, and vertices?
    Lead students to realize that the faces of a rectangular prism and a cube are all rectangles, but in the case of the cube, the rectangles are squares. A cube is a special rectangular prism.
  • Say:Take out your solid figures that have curved surfaces. Look at the sphere.
  • Ask:Does a sphere have any edges or vertices?  (no)  Why not?
    Students should realize that a sphere has no faces, so it can't have any edges or vertices.
  • Say:Look at the cone.
  • Ask:Does a cone have any edges? (no) Why not?
    Students should realize that a cone has only one face, and you need more than one face to form an edge.
  • Ask:Does a cone have any vertices?
    Lead students to see that a cone has no edges, but the point where the surface of the cone ends is called the vertex of the cone.
  • Say:Look at the cylinder.
  • Ask:Does a cylinder have any edges or vertices? (no) Why not?
    Students should realize that although a cylinder has two faces, the faces don't meet, so there are no edges or vertices.

Wrap-Up and Assessment Hints
Encourage students to explore more attributes of regular solid figures. Ask questions such as the following: Which solid figures have opposite faces that are parallel? (rectangular prism, cube, cylinder) Which solid figures have opposite faces that are congruent? (rectangular prism, cube, cylinder, pyramid) Which solid figure has all congruent faces? (cube) Through questioning strategies such as these, you will be able to judge your students' understanding of solid figures.


Houghton Mifflin Math Grade 3