Thursday, November 15, 2012



A. Discover the formula for finding circumference using pi and diameter
B. Solve problems involving circumference of a circle
C. Work cooperatively in groups

A. Circumference of a Circle
B. BEC PELC Math V 1; 1.1; 2; 2.1.1-1.4
C. pictures, circular/round objects, string, ruler, activity sheets
D. Cooperation

III. Procedure
A. Preparatory Activities
1. Review
Who is the Father of Geometry? Find the perimeter of the following plane figures/polygons to find out.(Draw your figure beside the numbers.)
1.                                    2.                                    3.

4.                                    5.                                    6.

 ______     _____     _____     _____      _____      _____
    3           1               5               4           2              6  

2. Motivation
Ask: How well are you familiar with different circles around you? Identify the following circular objects shown in the following pictures.
·         Show pictures of circular objects and let pupils raise their hand if they know the object.
Ask: Do you know that circles just like polygons also have perimeter? How do we call the perimeter of a circle? How do we solve for the distance around the circle?

B. Developmental Activities
1. Presentation
Group Activity: Exploration with Discs
·         Divide Pupils into 5 groups and let them gather in circle.
·         Orient the pupils on the rules and proper decorum during group activity.
·         Distribute the needed materials and activity sheets. Instruct pupils to read carefully the directions.
·         Emphasize the importance of cooperation to successfully accomplish the task.
·         Guide pupils while the activity is going on. Have them focus on the following questions:
a.    What is the distance/length around the circular object?
b.    What is the distance/length across the circular object?
c.    What is the value if we will divide the length around the circular object by the length of the circular object? Express your answer to the nearest hundredth.
·         Let pupils write their results in the matrix written in the chalkboard. Have them observe and compare their result with the result of the other groups.
Ask: What have you noticed with your results? Are the results similar? Why do you think are they similar?
·         Introduce that the distance/length around the circular object is called the CIRCUMFERENCE. Relate that the CIRCUMFERENCE is actually the “PERIMETER” of a circle. The distance across the circular object is called the DIAMETER. Half the diameter is called the RADIUS.
·         Elaborate that long time ago, people started to notice that the Circumference of a circle is approximately 3 times the diameter. Discuss that at present, mathematicians have accurately solved this value to 3.1415926535 or simply 3.14. This value is called as pi (π).
·         Present the equation to the class: π = . Explain that if this equation would be rearranged, we can have C= π x d. Since the radius is half the diameter, circumference can also be solved through C= π x 2 x r.
·         Let pupils memorize the formula in finding the circumference through body movements.

Provide the following example:
Liza wants to put a lace around a circular pillow. If the pillow has a diameter of 20 dm, how long should be the lace?
Let pupils analyze the problem using STAR Strategy.
ü  S-Search the Problem
The circular pillow has 20 dm diameter.
I need to use pi which is equal to 3.14.
I need to find the circumference of the pillow to find the length of the lace.
Or simply,    d= 20; pi= 3.14 C= ?
ü  T-Translate the problem into an equation
C= π x d     C=3.14 x 20 dm
ü  A-Answer the Problem
C=3.14 x 20 dm
C= 62.8 dm    The length of the lace needed is 62.8 dm.
ü  R-Review the Solution
Since π = C/d, hence 62.8 dm/20 dm should be equal to 3.14.
62.8 dm/20 dm = 3.14

Provide other examples:
a. A circular fountain has a diameter of 4 m. What is the circumference of the fountain?
b. A circular aviary needs to be surrounded with screen.  If the aviary measures 15 ft across, how long should be the screen needed to surround the aviary?

2. Fixing Exercises (Pair-Share Activity)
Find the circumference. Use pi=3.14
1.                                                       2. 

3. What is the circumference of a circle with a diameter of 4.5 cm?
4. A round wooden table has a radius of 2 m.  Find its circumference.
5. Give the circumference of a clock with 9 inches as its diameter.

3. Generalization
·         What is the circumference of a circle?
·         What is pi? What is the value of pi?
·         How do we solve for the circumference of a circle?

C. Application
Imagine you’re the person in the following problems then give your solution.
1. You are a gardener. A round flower plot needs to be fenced with wire.  If it measures 9 m across, how long should be the wire needed to fence around the plot?
2. The distance around a circular running field is 75 m. If you are a runner and you want to run across the field, how far would your run be?

IV. Evaluation
Read the problem and show you solution.
1.                                                       2. 

3. Give the circumference of a circle with 3.5 cm as its radius.
4. What is the diameter of a round mirror if its circumference is 35 dm?
5. A rubber tire measures 3 ft across. Find its circumference.

V. Assignment
Try to look for round/circular objects around your house. Then complete the table below.

e.g. plate

Prepared by:

Teacher I
A. Bonifacio Elementary School


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