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Finding Circumference |
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Key Idea
The circumference,
diameter, and radius
of a circle have
special relationships
that can help you
measure circles. |
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Vocabulary
• circumference
• diameter (p. 336)
• radius (p. 336)
• pi |
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Materials
• 5 circular objects
• string
• metric ruler
• calculator |
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How are the measurements of a circle related to one another? |
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You
know how to find the perimeter of figures that
have straight sides. But a circle does not have
sides.
So, you need to use a different method to find
the circumference
of a circle. |
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| a. | Find
5 circular objects that you can measure, such
as a can,
a clock, a plate, a bicycle tire, and so on. |
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| b. | For
each object, measure the diameter of the circle
to the
nearest mm. Make sure that your diameter goes
through the center of the circle. |
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c. |
Wrap string around the outside of each
object. Then use a ruler to measure the
length of the string to the nearest mm.
This is the circumference of the circle.
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| d. |
Record your measurements in a table like this
one and look for patterns. You can use a calculator
to find
C
÷ d
in each case. |
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| e. |
What pattern do you
see between your
measurements of
the diameters and
the circumferences?
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