# Exploring Circles

Warmup

Activity #1

How to Draw a Circle.

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

• Then draw and label Circle A, with a diameter of 6 cm.

• Draw and label Circle B, with a radius of 5 cm.

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

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

• Use the compass app below to recreate one of these designs.

Activity #2

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.

Activity #3

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.

• Study all the lines that are drawn inside the circle and answer the questions that follow.

(1.) Write down examples of a diameter to the circle. Explain your reasoning.

(2.) Write down examples of a radius to the circle. Explain your reasoning.

Challenge #1

Sort these pictures into two groups.

Explain why you sorted the objects like you did.

Challenge #2

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.

Challenge #3

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.

Quiz Time