Circumference Length

A tire is 40cm in diameter, as shown. Question: how many full turns of this tire corresponds horizontally to how many centimeters?

• Wrap the wheel with string.
• Mark the beginning and end of this loop on the string.
• Extend it far enough and measure the length of the circumference corresponding to the wheel.

Measuring this dimension, you will find approximately 125.6cm, which is a little over 3 times its diameter. Let's see how to determine this length by a non-experimental process.

You have probably heard of an old mathematical discovery:

Dividing the length of a circumference (C) by measuring its diameter (D), we always find a value approximately equal to 3.14.

Like this:

The number 3,141592… corresponds in mathematics to the Greek letter (reads "pi"), which is the first reading of the Greek word perimeter. It is usually considered = 3,14.

Soon:
Using this formula, we can determine the length of any circumference. We can now check with the formula the experimentally obtained wheel length.

C = 2r C = 2. 3.14 · 20 C = 125.6 cm

 3,141592…
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