A circle is a round, two dimensional shape that looks similar to the letter ‘O’.

In strict mathematical language, circle refers to the boundary of the shape while ‘disk’ is used to refer to the whole shape, including the inside.

A straight line from the center of a circle to the edge is called the radius.

A straight line that passes from one side of a circle to the other through the center is called the diameter.

The distance around the outside of a circle is called the circumference.

All points on the edge of a circle are the same distance to the center.

The value of Pi (π ) to 2 decimal places is 3.14, it comes in handy when working out the circumference and area of a circle.

The circumference of a circle can be found with the following formula: Circumference = π d

The area of a circle can be found with the following formula: Area = π r²

An arc is part of the circumference of a circle.

A chord is a straight line joining two points on a circle, the diameter is an example of a chord (the longest possible one).

A segment is the region between a chord and the arc it joins.

A tangent is a straight line that touches a single point of a circle.

A sector is the region between an arc and two radii.

The full arc of a circle measures 360 degrees.

A semicircle is a shape that forms half a circle, the arc of a semicircle measures 180 degrees.

Circles have a high level of symmetry.

A circle has the shortest perimeter of all shapes with the same area.

The circle shape is a favorite of humans and can be seen in many designs.

The invention of the wheel (a circle shape) was one of the most important in human history.

Circles and spheres are also frequently seen in nature, can you think of some examples?