Circles and nets

I can name the parts of a circle, double the radius to find the diameter, and match a net to its 3-D shape.

For grown-ups: this lesson in words

Year 6 · Maths

Here is a circle. The curved line all the way round its edge is called the circumference.
The circle is cut into 2 equal halves. The straight cut goes right across, through the centre.
That straight cut line, right across the circle through its centre, is a diameter.
Picture: A circle cut into 2 equal parts, with 0 parts shaded.
Now the circle is cut into 4 equal quarters.
The 2 cut lines are both diameters. They cross at the centre.
From the centre out to the circumference is a radius. Here there are 4 radius lines, all the same length.
Two radius lines, end to end, make one diameter. So a diameter is twice as long as a radius.
Picture: A circle cut into 4 equal parts, with 0 parts shaded.
A bar model shows it. The whole bar is the diameter, 8 cm.
It is made of 2 equal parts: a radius of 4 cm and another radius of 4 cm.
diameter = 2 × radius, so 2 × 4 = 8
radius = diameter ÷ 2, so 8 ÷ 2 = 4
Picture: A bar model: the whole, Diameter, 8, is split into Radius 4 and Radius 4.
Your turn: This circle has a radius of 5 cm. What is its diameter?
Picture: Radius 5 cm: a round flat shape with 1 curved side.
Choose one:
- 2.5 cm
- 5 cm
- 10 cm
Answer
The answer: 10 cm
10 cm. The diameter is twice the radius: 2 × 5 = 10.
Picture: A bar model: the whole, Diameter, 10, is split into Radius 5 and Radius 5.

circumference:: The curved line all the way round the edge of a circle.
radius:: A straight line from the centre of a circle to its circumference.
diameter:: A straight line right across a circle, through its centre. It is twice the radius.
net:: A flat pattern of faces that folds up to make a 3-D shape.
face:: A flat surface of a 3-D shape.

This is the first part of the lesson. Grown-ups can unlock every lesson in the grown-ups area.