Circles (F)

So what is a circle? In geometry terms it is defined as the set of points, or a path, such that every point on the path is the same distance away from another point, the centre of the circle. Imagine a post in the middle of a big field. A dog is tied to the post, on a lead that is 5 metres long. If the lead is always tight, what shape on the ground will the dog trace out as it runs around? The lead would be the radius of the circle, and the dog’s path is the circumference.

Circles are so special that they have their own names for their different parts. You need to be familiar with them, and know how they are related to each other. And then there is pi… Pi is just a number, and because it isn’t exact, mathematicians decided to give it a name and a symbol to make it easier to work with. If you measured the diameter, d, and the circumference, C, of a number of circular objects, and divided C by d, you should always get an answer just a bit bigger than 3. For any given circle, pi is the ratio of the circumference to the diameter.

Know your way around circles so you don’t end up in a spin!