A growing wheel

Increase the diameter. Notice how the contour also increases. The figure represents an ideal circle model.

Explore the controls and explain what changed in your own words.

A walk through round shapes

Choose a circular lid. Wrap a string around it, without stretching it, and mark the length of the outline. Then measure with the ruler the width that passes through the center, from one edge to the other: this is the diameter.

Compare without memorizing a formula

Cut a strip of paper the length of the diameter. Approximately how many of these strips fit around the contour? Repeat with another lid. You will notice a little more than three diameters on the outline. This relationship will be studied with the number π in the next track.

Registration challenge

His group found a diameter of 10 cm and a contour of approximately 31 cm. Do three diameters cover the entire measured contour? How much is missing in this comparison?

Check out the discovery

Three diameters add up to 30 cm. Approximately 1 cm is missing from the measured contour of 31 cm. These values ​​are approximate records of an experiment.

Your turn: draw the lid, indicate the diameter and record the contour with the unit. An experience helps to investigate; measuring does not demonstrate that a number is irrational.