A circular shape or object is one that is in the form of a circle. How many of these circular objects can you name? The radius (or ‘radii’ for plural) is the length of a straight line from the ...

A model of the famous toy known as a spirograph. A circle of radius r (see blue circle below) is allowed to roll around the inside of a circle of radius R (see black circle below). We assume that the ...

That's the distance right across the centre of the circle. The diameter is always twice as long as the radius. And now the circumference. That's the distance all the way around the side of the circle.