Make music with straws
This online resource investigates different sound frequencies.
The resource is an instructional guide for building pan pipes made of drinking straws to demonstrate that different musical notes have different frequencies.
The instructions include how long to cut each straw for particular notes, and a guide to playing basic nursery rhymes using a number system.
This activity would make a good introductory lesson to sound waves or an extension for more able students to discuss frequencies and resonance. It should take approximately 30 minutes.