M3.6.6 For the adult
Circles
How far is it all the way round a round table?
What this chapter teaches
The radius goes from the centre to the edge, the diameter goes across through the centre, and the circumference is the distance round. Circumference ÷ diameter is the same for every circle, about 3.14, which is π rounded. The area is π × r × r.
Three questions to ask
There is no one right wording. Listen for the idea.
- How can you show that the distance round a tin is a little more than three times the distance across?
- Why does the area rule use the radius and not the diameter?
- What is the circumference of a circle with a diameter of 10 cm, using 3.14 for π?
After the chapter, the learner can
- Name the radius, diameter and circumference of a circle
- Measure round tins to see that circumference ÷ diameter is about 3.14
- Find the circumference and area of a circle
What they copy into their notebook
Diameter = 2 × radius. Circumference = π × diameter, about 3.14 × diameter. Area = π × r × r. π is about 3.14, a rounded value.