153
Solid shapes
Textbook: Part 4, lesson 143, pp. 58–59
GoalSolid shapes: cube and cuboid; faces and edges; areas of faces.
New words
cube · kubcuboid (rectangular box) · kuboidface · yoqedge · qirra
Explanation
The cube and the cuboid are solid shapes. Their faces are flat shapes, and their edges are the segments where faces meet. A cube and a cuboid each have 6 faces and 12 edges. All faces of a cube are equal squares and all its edges are equal. The faces of a cuboid are rectangles: opposite faces are equal; 4 edges are lengths, 4 are widths, 4 are heights. The sum of the areas of all faces is the total surface area.
Worked examples
Cuboid 5 cm, 4 cm, 2 cm: faces 5 × 4 = 20, 5 × 2 = 10, 4 × 2 = 8 cm² (two of each).
A cube with edge 3 cm: one face is 3 × 3 = 9 cm², total surface 6 × 9 = 54 cm².
Class activity
“Box hunt”: children find cube- and cuboid-shaped objects in the room (matchbox, book, dice). They count the faces and edges with a finger and fill in a table.
Practice
1
How many faces does a cube have?
6
2
How many edges does a cuboid have?
12
3
What shape are the faces of a cube?
square
4
One face of a cuboid is 6 cm long and 3 cm wide. What is its area in cm²?
18
5
The three different faces of a cuboid are 18, 12 and 6 cm² (two of each). What is the total surface area in cm²?
72