Objectives:
Students will use a ruler to measure diameters of circles and then find
area and circumference of circles.
M11.C.1
On your paper, label each
Vocabulary word:
-circle
-center
-diameter
-radius
-semi-circle
-major arc
-minor arc
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The circumference of a circle is the distance around
the circle. The number pi (π) is the ratio of the
circumference of a circle to its diameter.
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In your own words, what is another word for
circumference? Think about the distance around
other shapes such as a triangle or quadrilateral.
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The circumference of a circle is π times the diameter.
C = πd or C =2πr
Why are both formulas
above correct when finding
the circumference?
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*Circumference is noted using
single units. Ex: inches, feet, etc.
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The area of a circle is the number of square units the
figure encloses.
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The area of a circle is π times the radius squared.
A = πr²
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**Area in noted using squared units. Ex: inches
squared, feet squared, etc
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Circle G has a radius of 14 cm. Find the
circumference of circle G in terms of π. Then find the
circumference to the nearest tenth.
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Find the area of circle B in terms of π. Then find the
area to the nearest tenth.
B
8.4 in
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Using a ruler, measure the diameter of your 5
circular items and record them in the chart provided.
Continue to fill in the chart by finding the radius,
area, and circumference of each circle.
Once your chart is complete, give it to your partner
along with the circular items so that he/she can
check your measurements and calculations.
With your partner, answer the analysis questions.
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Circles that lie in the same plane and have the same
center are concentric circles.
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A circular swimming pool with a 16 foot diameter will
be enclosed in a circular fence 4 feet from the pool.
What length of fencing material is needed? Round to
the nearest whole number.
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Brainstorming with your partner, make a list of at
least five jobs/careers that would require you to find
the area or circumference of a circle. What
companies would hire these types of workers?
Write two paragraphs incorporating the careers and
jobs that would require finding area and
circumference. Would you be interested in one of
those jobs in the future?
You will share your ideas with the class.