One student holds the yarn and stands still, others roll the wheel about the circumference. Other teams of students are tasked with determining the diameter. See how close to pi the island is. On Pohnpei the height of the mountains will be a problem. On Moen and Kosrae the lack of a circumferential road will likely prove daunting.
Objects can be anything found anywhere.
Graph is simple linear, slope is pi directly. Sphelocity Obtain hard spheres. Golf balls, shooter marbles, ball bearings from large engines will all work well. Bigger is better, with bowling balls the best. Bowling balls will require ramp modifications.