The Perimeter Of A Shape.

1
The Perimeter Of A Shape.
2
The Idea Of Perimeter.
Perimeter is the distance around the outside of a
shape.
What is the perimeter of the shapes below ?
(1)
P
6
4
6
4
P
2 x
( 5.6 8.9)
P
20cm
P 29m
3
P
3
4
5
P
12cm
P
8 x
10
P
80 m
4
What Goes In The Box ?
Calculate the perimeter of the shapes below
P 26cm
P32.5cm
P 34.1m
P72cm
5
The Perimeter Of A Circle.
Look at the circle below
Circumference.
Diameter
Key Question. How many times bigger is the
diameter of the circle compared to the diameter ?
The circumference is a bit more than three times
the diameter.
6
Estimating The Circumference.
If we know that the circumference of a circle is
roughly three times the diameter , then estimate
the circumference of the circles below
Circumference 3 x diameter
C 3 x
6cm
Circumference 3 x diameter
C 3 x
9m
C 18 cm
C 27m
7
The Number Called Pi.
After a great deal of measuring and calculating ,
Greek mathematicians came up with a better
estimate of how many times bigger the
circumference was compared to the diameter.
Key Fact. They found that the circumference was
3.14 times bigger than the diameter. They called
3.14 Pi after a letter in the Greek alphabet. The
letter pi is written as
The Circumference Of A Circle.
Circumference Pi x Diameter
8
Calculating The Circumference.
Calculate the circumference of the circles below
C ? x D
C ? x D
? 3.14
D 10m
? 3.14
D 2.8cm
C 3.14 x 10
C 3.14 x 2.8
C 31.4m
C 8.8cm
9
What Goes In The Box 2 ?
Calculate the circumference of the circles shown
below
12.6cm
81.64m
14.4m
10
Perimeter Of More Complex Shapes.
Calculate the perimeter of the shapes below
P 12 (3.14 x12) ?2
P 12 18.84
P 30.8 cm
11
(3.14 x10 ?2)
P
10
16
P
26
15.7
P 41.7m
12
P
10
10
(3.14 x 20) x 0.75
P
20
47.1
P
67.1 cm