LESSON PLAN

Construction of 3D Objects

Apothem Team

Grade 3 · Geometry

LESSON AT A GLANCE

Warm-up

5 min

Explore

15 min

Consolidate

10 min

Practice

12 min

Exit ticket

3 min

Warm-up

Mystery object: pass around a closed box. Feel it without looking. How many faces? Edges? Corners (vertices)? Open and reveal. Were your counts correct? This activates tactile geometry knowledge before visual construction.

Explore

Net construction: students choose one 3D shape, fold a pre-drawn net to construct it, then build the same shape as a skeleton with straws and clay. Compare: what does the net show that the skeleton does not? (Faces.) What does the skeleton show that the net does not? (Spatial structure without distraction of surfaces.)

Consolidate

Practice

Students construct nets for 3 different 3D objects, record faces/edges/vertices for each, and sketch 2 cultural objects identifying the 3D shapes they contain. Exit ticket: how many faces does a cube have, and what shape are they?

Exit ticket

TIP The spatial visualization required to predict which net folds into which 3D object is one of the most challenging skills in elementary geometry. Give students many opportunities to fold and unfold before asking them to predict.

WORKED EXAMPLES

How many faces, edges, and vertices does a triangular prism have?

Faces: 2 triangles + 3 rectangles = 5 faces. Edges: 3 edges on each triangle + 3 edges connecting them = 9 edges. Vertices: 3 on each triangle = 6 vertices. Check: F + V = E + 2? 5 + 6 = 11 = 9 + 2. Yes.

Draw two different nets for a rectangular prism that is 2x3x1.

Multiple nets exist for any rectangular prism. One: a row of 4 rectangles (the long faces) with 2 rectangles flipped out on the sides. Another: a cross shape. Both fold into the same prism. At least 11 different nets exist for a cube alone.

MATERIALS

•Net templates (cube, rectangular prism, triangular prism, pyramid)

•Scissors and tape

•Straws and clay or connectors for skeletons

•3D object collection for reference

•Images of cultural objects: jingle dress bells, bentwood boxes, pithouses

WATCH FOR

!Students may count edges twice (once for each adjacent face). Trace each edge with a finger and count each physical edge once.

!Students may not recognize the same shape in different orientations. A triangular prism lying on its side looks different from one standing up: same shape, different orientation.