More geometry
Circles
A circle is a round 2D shape. Every circle has a centre. Let's learn how to spot circles and find their centre.
What is a circle?
A circle is a round, flat (2D) shape. Its edge is curved. A circle has no corners and no straight sides. Plates, wheels and clock faces are all shaped like circles.
The centre of a circle
Every circle has a centre — the point in the middle. All the points on the edge of the circle are the same distance from the centre.
Finding the centre by folding
You can find the centre of a paper circle by folding. Fold it in half exactly and open it out. Turn the circle a little and fold it again. The centre is where the two folds meet.
Circles are everywhere
Circles are all over the world — in art, in nature, in buildings and in our homes. As a wheel turns, it stays the same round shape.
Worked examples
Is it a circle?
- Look at the shape. Is it round with a curved edge?
- Check that it has no corners and no straight sides.
Answer: If it is round with a curved edge and no corners, it is a circle.
Finding the centre
- Fold the paper circle in half and open it out.
- Fold it again a different way and open it out.
- Find where the two folds cross.
Answer: Where the two folds meet is the centre of the circle.
Same distance to the centre
- Pick any point on the edge of the circle.
- Measure the distance to the centre.
- Try another point on the edge.
Answer: Every point on the edge is the same distance from the centre.
Where you see this in real life
- The wheels on a bike or a car are circles.
- A clock face is a circle.
- A round plate or a coin is a circle.
- The Sun and the full Moon look like circles.
Key words
- Circle
- A round, flat 2D shape with a curved edge.
- Round
- Curved all the way with no corners.
- Centre
- The point in the middle of a circle.
- Edge
- The curved outside line of the circle.
- Fold
- Bending the paper over to make a line, used to find the centre.