Perimeter of Circles

Saturday, 17 March 2012

05. The Amazing of "Pi"

Do you know the value of "pi"???

"Pi" cannot be written exactly as a decimal because it is a transcendental number; it's irrational. We know precisely how much it is mathematically, just like we know exactly how much the square root of 2 is. We can't write either pi or the square root of 2 as a fraction of integers (or in a repeating or finite decimal notation). "Pi" has a decimal representation which consists of an infinite number of non-repeating digits.

The value of "pi" can be determined by finding the ratio of the circumference of a circle to its diameter..

The value of pi to 100 significant figures is...

3.141592653589793238462643383279502884197169399375

10582097494459230781640628620899862803482534211...

Do this experiment by your own....

Divide the circumference by its diameter...
Complete the table below....

Round Objects Circumference (cm) Diameter (cm) Circumference / Diameter

---------------------- ----------------------------- --------------------- -------------------------------------

1. 50 sen coin

2. Plate

3. Car tyre

4 Roundabout

It doesn't matter how large of small the circle is, the ratio of the circumference to the diameter will always be around 3.142....

04. The "Diameter" and "Radius" of a Circle

By now, you should be able to know that the length of the diameter (D) of a circle is twice as its radius (r).

The relationship between the diameter and the radius of a circle is further illustrated as below:

1. The diameter of the circle is 2 inches.

[ ]True
[ ] False

2. The radius of the circle is 6 inches.

[ ]True

[ ] False

3. The diameter of a circle is the distance from the centre or a circle to any point on the circle...

[ ]True

[ ] False

4. If you place two radii end-to-end in a circle, you would have the same length as one diameter...

[ ]True

[ ] False

5. Every diameter is a chord, but not every chord is a diameter...

[ ]True

[ ] False

What do you think....?
Can you answer all the questions...?

03. Parts of Circles

A circle is a shape with all points the same distance from the centre. It is a simple shape of geometry consisting of a line forming a closed loop, every point on which is a fixed distance from a centre point.

The diagram shows a circle which consists of its major parts.

The circumference of a circle is the distance around it. The term “circumference” is basically similar to the terms “perimeter”. However, "Circumference" is just a special term for the perimeter when applied to circles.

The diameter of a circle is the distance across a circle through the centre point. In geometry , a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints are on the circumference. The diameters are the longest chords of the circle. In other words, all diameters of a circle have the same length, this being twice the radius.

The radius of a circle is any line segment from its center to its perimeter. By extension, the radius of a circle is the
length of any such segment, which is half the diameter. The plural of radius can be defined as radii.

Try the following quick test...
Discuss with your classmates...

01_Parts of Circles

Friday, 16 March 2012

02. Learning Outcomes

1. Measure the diameter & radius of a circle...

2. Measure the circumference of a circle...

3. Identify the relationship between the diameter & radius of a circle...

4. Discover the value of "pi"...

5. Find the circumference of a circle by using fromula...