π§ͺ Science π’ Maths and numbers
A circle
π In short
A circle is a round, closed shape where every point is the same distance from a point in the middle called the center. We see circles everywhere: wheels, plates, clocks, rings, the sun's disc and the full moon.
π€© Did you know?
- A circle has 360 degrees.
- The ancient Chinese used 3 as an approximate value for pi.
- The diameter is twice the radius.
- A sphere is the solid shape that's like a circle.
π Find out more
π Parts of a circle
The center is the point in the middle. The radius is a line from the center to the edge. The diameter is a line through the center from edge to edge, twice as long as the radius. And the circumference is the length all the way around the edge.
π How do we draw one?
We draw a circle with a tool called a compass: we fix its sharp point at the center and turn the pencil around it. You can also draw one with a string tied to a pencil, holding the other end down with your finger.
π‘ The amazing number pi
If you measure the circumference of any circle and divide it by its diameter, you'll always get about 3.14! This amazing number is called βpiβ and written with the letter Ο.
π― Why are wheels round?
A round wheel rolls easily because its center always stays at the same height. If a wheel were square, the car would shake and bounce!
𧩠Test yourself
1 What tool do we draw a circle with?
2 How many degrees are there in a circle?
3 A circle has ?? degrees.
4 Which picture shows βA circleβ?