Rubber band guitar

Materials
Kleenex box
rubber bands
pens

Results
Success

Working theory

Sound results from periodic (i.e. regular) vibrations. Changing the length, thickness, or tautness of a rubber band should change how it vibrates and what pitch it produces.

Experiment

We started by placing different sized rubber bands around an empty Kleenex box, strumming the part of the rubber band that was over the opening of the box (where the Kleenex come out). This created a muted and muddy sound. Thinking the rubber band was up against too much of the box, preventing sustained vibrations, we moved two pens under the rubber bands and strummed in between them, making a nice note. By changing the distance between the pens (lengthening or shortening the part of the rubber band that vibrated), we were able to systematically change the pitch we got.