Circumference

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Circumference

• (The perimeter of a circle)

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Necessary Vocabulary

• Circumference
• Radius
• Diameter
• Pi

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Circumference

• The distance around a circle
• It is a single-dimensional unit of length
• Represented in single units (not squared!)

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What would I need the know the circumference for?

• How much ribbon to put around the end of a jar
• How long should a hatband be
• How much tire is needed to fit around a rim
• How long a necklace should be to fit comfortably
  around your neck
• How many inches should a hat band or a helmet be
  to fit around your head?

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Radius

• A radius is a line segment with one endpoint on
  the circle and the other endpoint on the center.
  
• A radius is ½ of the diameter.

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Diameter

• a line segment that passes through the center of
  a circle and has both endpoints on the circle.
• The prefix DI means 2.
• A diameter is equal to 2 radii (there are no such
  things as radiuses)

Do or Di(ameter)!
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The circumference, the diameter and pi
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3
2
.14
This yellow line across the circle is a DIAMETER.
This tiny piece is equal to .14 of the diameter.
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Another animation of pi
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Pi

• The ratio of the circumference of a circle to its
  diameter.
• Pi tells us how many times the diameter will go
  around a circle
• We ONLY use pi with circles!

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The ratio of circumference to the diameter
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The Formula for Circumference

• Diameter
• (2 radius)
• Remember that a diameter is equal to 2 radii

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How to find the circumference
C 3.14 d C 3.14 14
C 43.96 mi
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How to find the circumference
C 2 r
35 yd
C 3.14 (2 radius) C 3.14 (2 35) C
3.14 (70)
C 219.8 yd
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TRY THESE!
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How to find the circumference
C d
C 3.14 d C 3.14 11
C 34.54 in
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How to find the circumference
C 2 r
2.5 in
C 3.14 (2 radius) C 3.14 (2 2.5) C
3.14 (5)
C 15.7 in
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How to find the circumference
C d
C 3.14 d C 3.14 5.8
C 18.212 m
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How to find the circumference
C 2 r
10 ft
C 3.14 (2 radius) C 3.14 (2 10) C
3.14 (20)
C 62.8 ft
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YouTube.com

• Radius, Diameter Pi Song on You-Tube
• A Rap About Circles
• The Circle Song
• Maths Pi Song
• Pi Song listing the numbers

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