Going Around in Circles

Purpose:	To reinforce mathematical concepts of diameter and circumference of a circle while comparing tree sizes around the school yard.
Season:	All
Materials:	Worksheet, Metric/English tape measure, Pencil
Description:	Students find the diameter of a tree given the circumference and the formula c= P d. The students then record the relationship between the diameter and circumference of a tree using a scatter plot line graph.
Procedure:	Have students work in pairs. Give each pair a tape measure and worksheet. Label ten trees in the school yard (1-10) by putting masking tape completely around each trunk. Have one student in the pair measure the circumference of the tree by putting the tape measure over the masking tape while the other student records the data. Once the trees are measured, each pair must compute the diameter of the tree at the point of the masking tape, using c= P d and P =3.14. Have students record the results on a scatter plot graph.
Questions:	What pattern do you see with the dots on the scatter plot? (The dots should be in the shape of an oval sloping upward.)
Extensions:	Use a lesson in estimation as a follow-up activity. Ask each pair of students to estimate the number of leaves on the tree. Discussion: (1) What is an estimate? and (2) Where and how can estimates be used? Students may be asked to guess the number of leaves first and then use a systematic technique, such as counting the number of leaves on a branch or two as close to the ground as possible and then counting the number of branches and multiplying to arrive at an estimate. Then compare results.