Gr 6 · 45 min

Surface area from a net

Unfold a triangular prism and add the areas of two triangles and three rectangles.

Ontario Gr 6 · Spatial Sense E2 · Common Core 6.G.A.4

Learning goals

Represent a prism with a net of rectangles and triangles
Use the net to find the surface area

Plan

1
Unfold5 minYou lead
Show the prism and its net side by side in FoldNets. Which faces match?
2
Triangles10 minStudents
Find the area of one triangle: ½ × base × height. The dotted line on each triangle is its height: about 4.33 cm for a 5 cm equilateral triangle, printed beside it.
3
Rectangles10 minStudents
Each rectangle is 5 cm by the prism's length.
4
Total and check15 minStudents
Add 2 triangles and 3 rectangles. Check against the surface area FoldNets shows, then build the prism.
5
Change it5 minYou lead
On the board, make the prism twice as long in FoldNets. Which areas change? Only the rectangles: 291.7 cm² in all.

To talk about

Why does a net make surface area easier to find?
If you double every length, what happens to the surface area?

The model

Open in the maker

Teach this lesson

The plan step by step beside the model, for the projector.

The lesson pack, a worksheet with answer keys, and assigning to a class come with the teacher plan. Sign in

Materials

Triangular prism net printed at real size, with edge lengths and the triangles' heights
Rulers, calculators

Worksheet questions

Face shapes
Which net?
Surface area

Go further: If the prism were twice as long (18 cm), what would its surface area be? Which faces change?

One sheet about the model students build, with its answer key at the end. For a quiz, versions A and B have different measurements, so neighbours can't copy.

Students see

Use the edge lengths on your net, and each triangle's height (the dotted line), to find the area of every face. Add them up, then build the prism.

Suggested assignment: Build it. Printing only: students print your net as it is and build it.