Learn About The Circumference of a Circle

1
Learn About The Circumference of a Circle

• Lesson for 5th graders
• By Mandy Hakkarainen

2
What is a Circle

• This is a circle
• A circle is the collection of points in a plane
  that are all the same distance from a fixed
  point.
• Some examples of circles in this room are Clock,
  door knob, garbage can

3
What is Circumference

• The circumference of a circle is the distance
  around it. It is measured in linear units
  (inches, feet, etc.).

4
What is the Radius

• The fixed point is called the center (P). The
  line segment joining the center to any point on
  the circle is called the radius (r).

5
What is the Diameter

• A line segment with both endpoints on the circle.
  A diameter always passes through the center of
  the circle.

6
What is Pi

• Pi is approximately equal to the decimal 3.14 or
  the fraction 22/7. Neither one of these values
  is exactly equal to pi, since pi is a special
  kind of number (an irrational number), but even
  though 3.14 and 22/7 aren't exactly equal to pi,
  they are close enough to do most calculations.

7
Circumference

• Most of the time we use a formula to calculate
  the circumference of a circle once either the
  radius or diameter is known.
• If we know only the radius we must use the
  formula C2rpi (rradius), because 2 times the
  radius equals the diameter.
• If we know the diameter we must use the formula
  CDpi (Ddiameter).

8
A Sample Problem To Try

• If you know that the radius 5.5, then according
  to the last formula
• C 25.5 3.14 34.54.

9
A Sample Problem to Try

• If we know the diameter is 11 then we use the
  formula
• C 113.1434.54

10
Student Resource Page

• Resource Web Page For Students
• Sample Worksheet

11
Teacher Resource Page

• Resource Web Page For Teachers
• Sample Worksheet
• Answers To Sample Worksheet