An Explorer lesson from the Great Lakes Collaborative in which students explore the relationship between diameter and circumference.
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Author: Laura Jewell
Here is a concrete hands-on way to teach meaning to the formula for the circumference of a circle. (pi x diameter).
- Several cylindrical objects of different sizes (coffee cans, soda cans, jars, cups, etc.)
- Measuring tape, preferably cloth so it wraps easily around Calculators (if desired).
Students should already understand that pi = 3.14, and is always a constant.
Ask students to measure the diameter of one of the objects by stretching the tape across the opening.
They should then apply the formula x d to get a measurement.
Then have students actually measure the circumference of the object with the measuring tape. They will find out that it is the same measurement as they calculated!
Repeat this procedure with the other objects you have prepared. Students will soon see that circumference is always 3.14 times the diameter of any round figure!
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