2
Flat faces and curved surfaces
Learner’s Book 1: Unit 2, p. 38
GoalUse the words face, edge, flat face and curved surface to describe a 3D shape.
New words
face · a flat side of a 3D shapeedge · where two faces meetcurved surface · a round part that is not flat
Explanation
3D shapes have faces. A face is a flat side. On a cube, every face is flat. Where two faces meet, there is an edge. Run your finger along a box and you will feel a sharp line: that is an edge. Some 3D shapes have a curved surface. A cylinder has two flat faces and one curved surface. A sphere has only a curved surface. Hold a tin, a box and a ball. Which ones have edges? Which ones have flat faces?
Worked examples
A cylinder has a flat face on the top and on the bottom. The side is a curved surface.
A sphere has no flat faces and no edges. It has one curved surface.
Test it with your hand: a tin has an edge that you can feel all the way round the top. A ball has no edge.
Class activity
Feel the shape: put a box, a ball and a tin in a bag. Without looking, feel one. Does it have a flat face? An edge? A curved surface? Say what you feel, then guess the shape and pull it out.
Practice
1
Does a sphere have an edge?
No.
2
Which shape has flat faces and a curved surface: cube, sphere or cylinder?
cylinder
3
What do we call the place where two faces of a cube meet?
an edge
4
Which shape has only a curved surface?
sphere