Encourage the students to make direct comparisons by blowing into first one tube and then another. By making systematic comparisons of pairs of tube, they can order the tubes according to pitch. Keep the student groups as well-separated as possible.

Students are reasonably successful in associating vibration with sound when they can directly observe the vibrating object, such as a guitar string. A vibrating column of air is much more difficult to conceptualize, as is the idea that vibrations can move out from the column toward a listener. If you have both a guitar and a recorder in the room, have students play a note on each. First, have the class trace the vibration from the guitar string to the students’ ears. Then do the same with the recorder.