80
STEM
Curriculum
Science
Technology
Mathematics
Engineering
Integrated
Math Application
Circumference of Circles
of these features must be included on your design drawings. This may
involve mathematical calculations.
To find the length of a border that includes a circular shape, you need
to find the circumference of, or distance around, the circle. See Figure A.
The formula for calculating the circumference of a circle is C = π × D and
is usually written:
C = πD
D stands for the diameter of the circle (the distance from one side
of the circle to the other through the center). See Figure B. The symbol π
(pronounced “pie”) represents the number 3.14 (rounded to two decimal
places). So, the circumference of a circle is 3.14 times its diameter.
For example, suppose your design includes a circle that is 8 inches
in diameter. The circumference of the circle would be:
C = 3.14 × 8 in. = 25.12 in.
Math Activity
Apply the formula explained above to calculate the answers to the
following problems.
1. Most bicycles used on the road have wheels with a 27-in. diameter.
Using the correct formula, calculate the distance a bicycle wheel
travels on the pavement when it turns one revolution.
2. Suppose that you have created a new bicycle design that calls for
30-in. wheels. How far would a 30-in. wheel travel on the pavement in
one revolution? After calculating the answer, think about the design
implications. Which tire would last longer (cover more distance before
failing)? Which tire would be more expensive to build? Why?
Circumference
Center of
circle
Center of
circle
Diameter
Radius
B A