Perimeter and circumference are not difficult mathematical concepts. Of course, the definitions of perimeter and circumference are important. Students need to get the idea that it is the distance around an object. (It's how far an ant would walk around the boundary, or how much fence it would take to build around the shape.) For a GSP exercise, click here.
One of the important ideas that should not be missed this lesson is the meaning of pi. To many, it is some magical number that never repeats, never ends, is 3.14..., and is represents by a wierd symbol.
Students need to know what pi really means. Do they realize at one time they were all "pi" feet tall? One possible exercise is for students to measure round objects and look for relationships between their diameter and circumference. For more accuracy, GSP could be used. The amount of information given the students should be altered depending on the time available. Click here for a GSP sketch on what students will hopefully realize.
Definition links lead to Intermath website dictionary. Click here to visit the Intermath site.