All About Circles

Jan 29, 2020 | Hinsdale

Here are some useful circle facts from KidsMathGamesOnline.com!

  • 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.

Circle circumference, diameter and radius

  • 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

Area of a circle

  • 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.

Circle arc, sector and segment

  • 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.