The Circle

1
The Circle

1. Know the names of a circles features
2. Calculate the circumference

Why am I doing this?
A wheel is a circle! Circles in design Mickey
Mouse is made from circles A real favourite SAT
and GCSE question
OK - What have I got to do?
2
Name these Features The distance from the centre
to the edge The distance from one side to the
other passing through the centre The distance all
of the way round the edge The blue line
3
The distance from the centre to the edge
RADIUS The distance from one side to the other
passing through the centre DIAMETER The distance
all of the way round the edge CIRCUMFERENCE The
blue line CHORD
Segment
Sector
4
APPROXIMATELY FINDING THE CIRCUMFERENCE
Level 5
5
APPROXIMATELY what is the relationship
(connection) between a circles diameter and its
circumference?
6
To APPROXIMATELY find the CIRCUMFERENCE MULTIPLY
the DIAMETER by 3 (C 3 x d)
Radius Diameter Circumference
4
8
12
10
5
15
18
30
42
7
To APPROXIMATELY find the CIRCUMFERENCE MULTIPLY
the DIAMETER by 3 (C 3 x d)
Radius Diameter Circumference
2 4 12
4 8 24
6 12 36
10 20 60
5 10 30
15 30 90
3 6 18
5 10 30
7 14 42
8

• OAA
• A circle has a diameter of 10 cm. APPROXIMATELY
  (ROUGHLY), what is its circumference?
• A circle has a circumference of 18 cm.
  Approximately, what is its diameter?

30 cm
6 cm
9
Calculate the Circumference Using the Correct
Formula
Level 6
10
How to calculate the circumference
Evaluate the CIRCUMFERENCE
Always, write the formula (rule)
C d C 3 X 12 C 36
Diameter 12 cm
The symbol is the Greek letter pi. It
stands for a number that can never be found
exactly. It is approximately 3.14
11
How to calculate the diameter from the
circumference
Always, write the formula (rule)
C d d C d C 3 d 40 3 d
13.333333
If the circumference is 40 cm. evaluate the
DIAMETER
Diameter ?cm
12
Diameter Radius Circumference
1 24
2 14
3 17
4 30
5 22
6 120
7 78
8 88
9 120
10 340

• Remember
• d 2 X r
• r d 2

13
Diameter Radius Circumference
1 24 12 75.36
2 14 7 43.96
3 34 17 106.76
4 60 30 188.4
5 22 11 69.08
6 120 60 376.8
7 156 78 489.84
8 176 88 552.64
9 38.22 19.11 120
10 108.28 54.14 340