Exploring Circles


How to Draw a Circle.

Spend some time familiarizing yourself with the tools that are available in this applet.

(1). Then draw and label Circle A, with a diameter of 6 cm.

(2). Draw and label Circle B, with a radius of 5 cm. 

(3). Draw and label Circle C, with a radius that is equal to Circle A’s diameter.

(4). Draw and label Circle D, with a diameter that is equal to Circle B’s radius.

(5). Use a compass app below to recreate one of these designs.


Draw Radius and Diameter of a Circle.

  • Use the geometric tool in the applet below to draw a circle. ​
  • Draw and measure a radius and a diameter of the circle.


Name the Radius and Diameter of a Circle.

Here is a circle with center H and some line segments and curves joining points on the circle.

(1). Identify example(s) of a diameter. Explain your reasoning.

(2). Identify example(s) of a radius. Explain your reasoning.


Sort these pictures into two groups.

Explain why you sorted the objects like you did.


On January 3rd, Earth is 147,500,000 kilometers away from the Sun. On July 4th, Earth is 152,500,000 kilometers away from the Sun. The Sun has a radius of about 865,000 kilometers.

Could Earth’s orbit be a circle with some point in the Sun as its center? Explain your reasoning.


Lin measured the diameter of a circle in two different directions. Measuring vertically, she got 3.5 cm, and measuring horizontally, she got 3.6 cm. Explain some possible reasons why these measurements differ.