Lesson 2: Circumference of a circle
Resources: five cent, ten cent, and a twenty-cent coin; and marker pen
For this activity, you need a ruler. Place the ruler on a flat surface and make sure the ruler stays in place.
In order to find the circumference of any coin,
- With a marker, make a small mark near the edge of the coin.
- Align the mark on your coin with the beginning of the coin.
- Roll the coin along the ruler until the mark on its touches the ruler again, make the coin move one revolution.
- With the pencil, mark the point on the line where the coin gets to after one revolution.
Consequently, in order to determine the diameter of any coin,
- Place the coin over the ruler with the beginning of the coin placed at zero, until the end of the coin covers the ruler. Then determine the length of the ruler covered, which will be the diameter.
Approximately how many diameters of the twenty-cent coin are equal to its circumference?
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≈ is the symbol for “approximately equals”
For a twenty-cent coin: 1 circumference ≈ ______diameters.
Now do the same with ten-cent and five-cent coins. Roll each of the coins along the ruler to determine approximately how many diameters are equivalent to its circumference.
For a ten-cent coin: 1 circumference ≈ ______diameters.
For a five-cent coin: 1 circumference ≈ ______diameters.
Were your answers very different for different sizes of coins? ______
Exercises:
- A farmer has a block of land and he wants to make a circular enclosure for the animals. The total fencing that he has bought is 11metres.. What would be the maximum diameter and radius of the circular enclosure? Hint: circumference = ∏ diameter
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- A farmer has bought a total fencing of 24metres. He wants to make a circular enclosure for his animals. Calculate the diameter of a circle, given ∏ as 22/7.
Hint: circumference = ∏ diameter
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