CIRCLE
NO  OBJECT  CIRCUMFERENCE
(C) 
DIAMETER
(D) 
RATIO
(C : D) 
1  Glue Cap  9cm  3cm  3 : 1 
2  Paint  12cm  3cm  4 : 1 
3  Venqua Gallon  82cm  22cm  41 : 11 
4  Fire Extinguisher  50cm  15cm  10 : 3 
5  Bucket  76cm  21cm  76 : 21 
6  Bamboo  9cm  3cm  3 : 1 
Project : Finding the Approximate of π
Pictures :
Information about circle :
A circle is a plane curve consisting of all points that have the same distance from a fixed point called center.
Parts of a Circle:
1.The radius of the circle is a straight line drawn from the center to the boundary line or the circumference. The plural of the word radius is radii.
2.The diameter is the line crossing the circle and passing through the center. It is the twice of the length of the radius.
3.The circumference of a circle is the boundary line or the perimeter of the circle.
4.The chord is a straight line joining two points on the circumference points of a circle. The diameter is a special kind of the chord passing through the center.
5.An arc is a part of the circumference between two points or a continuous piece of a circle. The shorter arc between and is called the minor arc. The longer arc between and is called the major arc.
6.A semicircle is an arc which is half of the circumference.
7.A tangent is a straight line which touches the circle. It does not cut the circumference. The point at which it touches, is called the point of contact.
How to find Circumference :
Circumference is the distance around the outside of a circle, just as the perimeter of a polygon is the distance around the outside.
The circumference can be found by multiplying the diameter of the circle by the number π (pi). To obtain an approximation, we will use the approximation 3.14 for π. One way the formula can be written is:
Example
The circumference of the circle with diameter of 10 cm
can be found using the formula:
C = π × d
then using 3.14 to approximate π,
C = 3.14 × 10
= 31.4
The circumference is 31.4 cm
If the radius is given, the circumference can be found by doubling the radius and then multiplying that product by the number π (pi). The formula can be written using radius:
Example
The circumference of a circle with the radius of 6 cm.
can be found using the formula:
C = 2 × π × 6
then using 3.14 to approximate π,
C = 2 × 3.14 × 6
= 37.68
The circumference is 37.68 cm.
How to find the Area of circle :
The area of a circle can be found by multiplying radius by radius by the number π (pi). The formula can be written as:
Example
The area of a circle with radius of 6 cm.
can be found using the formula:
A = π × (6)2
then using 3.14 to approximate π,
A = 3.14 × 6 × 6
= 113.04
The area is 113.04 cm2
NOTE: If the diameter is given, you must first divide the diameter in half, then calculate the area. The area formula only uses the value of the RADIUS.
an arc can be measured either in degrees or in unit length. In Figure 1 , l is a connected portion of the circumference of the circle.
