1. Using practical work
To explore and investigate polyhedra, it is important to have examples in your classroom. There are several commercial plastic building sets to make 3D objects that can be bought to use in the classroom, but it is as easy to make your own from recyclable materials such as plastic, card and thick paper. Making their own shapes helps pupils understand the properties of shapes better.
Plastic drinking straws can be used with thread and wire to build ‘skeletons’ of 3D models. As a teacher, make it a habit to keep objects that may be useful in the classroom – for example, always keep a straw whenever you buy a cool drink. Ready-made nets of various solids that fold up for storage can be used to help pupils explore the difference between 2D shapes and 3D objects.
Case Study 1: Differentiating between 3D objects and 2D shapes
Mrs Yomba, a primary teacher in Lindi, Tanzania, wanted her pupils to be aware of the difference between 3D objects and 2D shapes. She knew this was sometimes a difficult concept for them.
She described 3D objects as those ‘one can pick up, like books, pens, desks, etc.’. She said that 2D shapes are things you can see but that you cannot pick up: an image of a horse on a photograph, or a painting of a person, even a square drawn on paper. She said, although one can pick up the photograph or the painting, one cannot pick the horse out of the photograph or the person out of the painting.
She then invited them to suggest other things that could be regarded as either 2D or 3D in the classroom. Some pupils were quite excited about the distinction, but others really struggled to believe that a piece of paper or a window are 3D objects because they were ‘too thin’.
Mrs Yomba decided then to give her pupils homework. She asked them to go home and tell their parents about what they had learned, and that their homework task was to bring a list of at least ten things from home or the local environment that are 3D. She believed that by doing this they would consolidate the work they had done in class.
Activity 1: Understanding 3D shapes or polyhedra
Before you teach this lesson, you need to collect or make some 3D objects and keep these in a box (see Resource 1: Collecting and making shapes and objects).
Organise your class into groups of between six and eight. Ask your pupils to look carefully at the shapes and objects in the box. Ask your pupils what shapes, like squares and rectangles, they can see in the objects.
Tell them the names of the objects:
- Prism e.g. cube, cuboid, cylinder
- Pyramid e.g. cone, sphere
Ask them if they know other objects that look like these shapes around the school and near their homes.
Explain that all the solids, except the cylinder and sphere, are also called polyhedra. Ask them: ‘Why do you think cylinders and spheres are not considered polyhedra?’ (See Key Resource: Using explaining and demonstrating to assist learning for some ideas to help you.)
Tell them that the word polyhedron is from a Greek word for ‘a seat’. Prisms and pyramids have many flat surfaces like seats but a cylinder is not a polyhedron as it has a curved ‘surface’.
Finish the activity by asking each group to count the surfaces on each object. Ask them to record their answers in their books. Share each group’s answers as a class.
For homework, ask them if they can see any of these shapes on their way home – or at home – and report back the next day.