Transcript Circles & Circumference

Review
• Multiplying decimals: 3.2 x 5.12
• Multiplying fractions and whole numbers:
5 x 2/3
Circles, Pi, & Circumference
The outside of the circle is called
circumference
The circumference is the distance around the
circle.
The midpoint of a circle is
center
The line drawn from the centre
to the circumference is …
radius
The line drawn from one circumference
through the centre to another
circumference is …
diameter
radius
The diameter cuts the circle in half!
A line that connects one point on the edge
of the circle with another point on the
circle is called ….
chord
The chord that passes through the
centre of the circle is the diameter.
A segment ie. part of the
circumference of the circle is
called an ...
a r
c
Parts of the Circle
chord
diameter
centre
radius
arc
The Definition of Pi
• Pi, not Pie.
• 1.The 16th letter of the Greek alphabet is P or p,
corresponding to the roman p.
• 2. A number, represented by said letter,
expressing the ratio of the circumference of a
perfect circle to its diameter. The value of pi has
been calculated to many millions of decimal
places, to no readily apparent pattern.
Pi Equals?
• π = circumference/diameter
3.141592653589793238462643383279502884197169399
≈ 3751058209749445923078164062862089986280348253
4211706798214808651328230664709384460955058223
1725359408128481117450284102701938521105559644
6229489549303819644288109756659334461284756482
3378678316527120190914564856692346034861045432
6648213393607260249141273………. (on and on and
on)
• π ≈ 22/7 or 3 and 1/7
• We will use 3.14
Use Pi to Find:
• The area of a circle = πr2
• Circumference of a Circle = πd or 2πr
• Surface Area of a Sphere, Volume of a
Cone, Cylinder and Sphere all are
formulas that involve π.
The formula to find Circumfren ce is :
C  2  r or C   d
22
  3.14 or
7
BACK
Find the Circumference of the circle.
C  2 r
C  23.142
C  12.56 yd.
BACK
Find the circumference using the diameter.
C πd
C  3.1410
C  31.4 in.
BACK
Find the circumference of the circle.
C πd
C  3.1416
C  50.24 ft.
BACK
How would you find the diameter of
a circle if you were only given the
circumference?
d  C 
Find the diameter of a circle that
has a circumference of 66.
d  66  3.14
d  21
BACK
Videos
• http://www.brainpop.com/math/numbersan
doperations/pi/
• http://www.youtube.com/watch?v=8cazxAL_tU
• http://www.youtube.com/watch?v=mZ4CP
0vTgEE