Water Bottles:

Resonance

INTRODUCTION

All objects have a natural rate of vibration depending on their size and shape. When two objects have the same natural rate of vibration, one can make the other vibrate. If two guitars are tuned exactly the same, a string vibrating on one will cause the same string to vibrate on the other. The two instruments are said to be in resonance.
Acoustics are the study of how sound waves behave and how they can be controlled. Acoustical engineers design auditoriums with a combination of sound-absorbing and sound-reflecting materials. In this manner, they can control echo and reverberation. Many auditoriums are also designed so that voices can be heard from the stage to the back of the room without artificial amplification.

MATERIALS

• 2 identical glass bottles
• Disinfectant wipes

WHAT TO DO

1. Give pairs of students two glass bottles. Have one student hold the mouth of one of the bottles near his or her ear.
2. Have the second student stand about 1 meter to one side of the first student and blow across the top of the other bottle until a clear note is produced.
3. Let the students take turns listening to the resonating notes.
4. Wipe the bottles with disinfectant wipes.

QUESTIONS

1. How does the bottle held near the student’s ear respond?
2. Name a part of the school where echoes are produced often. (e.g. gym, hallway)
3. Name a part of the school where sounds are more muffled. (e.g. carpeted classrooms)

SOURCE

"Sound Fundamentals." Robert W. Wood, Chelsea House Publishers: Philadelphia, 1999, p. 47-48.

© S. Olesik, WOW Project, Ohio State University, 2000.