10.3 Circumference of a Circle
Objective: Find the circumference of a circle.
Joseph Williams GESD jwilliams@gesd40.org
Image: 'Olive oil bubble variations'
www.flickr.com/photos/21649179@N00/2141140776
1

What part of the circle does he draw?
Image: 'tips'
www.flickr.com/photos/78364563@N00/13553883
2

Circle ­ the set of all points in a plane that are
the same distance from a point called the
center.
Image: 'Olive oil bubble variations'
www.flickr.com/photos/21649179@N00/2141150298
3

Center ­ The point inside a circle that
is the same distance from all the points
on a circle.
4

Radius ­ The
distance from the
center of a circle to
any point on the
circle.
Image: 'blood orange'
www.flickr.com/photos/33602849@N00/2262073
5

Diameter ­
the distance
across the
circle
through its
center.
Image: 'blood orange'
www.flickr.com/photos/33602849@N00/2262073
6

Circumference ­
the distance
around a circle
(the perimeter of a
circle).
Image: 'blood orange'
www.flickr.com/photos/33602849@N00/2262073
7

pi ­ the
ratio of the
circumference
of a circle to its
diameter.
(3.14) Image: 'Pi sculpture'
www.flickr.com/photos/35034351734@N01/21582841
8

Diagram of a Circle
Radius
Diameter
Center
Circumference
9

Label Each Circle
Center Radius
Diameter Circumference
10

Multiplying Decimals
1. Line up the numbers.
2. Multiply like you would any
other number.
3. Count over for your decimal
place in your answer.
Image: 'Blue power3'
www.flickr.com/photos/73491156@N00/391970523
11

Finding Circumference
5
C = 2 r C = 2 3.14 5
C = 31.4
12
C = d C = 3.14 12
C = 37.68
12