Abstract

Objective

The goal of this project is to determine the relationship between musical note frequency and fluid level when producing notes by blowing over the top of a partially-filled bottle.

Introduction

Some musical instruments produce sound from vibrating strings, others from vibrating reeds, and still others from resonating columns of air. In this project you'll study a simple example of the latter type of instrument: a narrow-necked bottle partially filled with water.

You can learn about the physics behind this type of instrument by studying resonance in closed-end air columns (Henderson, 2007b; University of Virginia, date unknown). Can you figure out the relationship between fluid level in the bottle and the pitch produced when you blow across the top of the bottle? How about the note produced by tapping on the side of a partially-filled bottle? Does it change in the same manner?

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Sound
• Sound waves
• Standing waves
• Musical note names and frequencies
• Resonance
• Closed-end air columns

Questions

• What standing wave patterns are produced in a closed-end air column?
• How is the frequency of the note produced related to the length of the column?

Bibliography

• This is a great general resource on the physics of sound:
  Henderson, T., 2007a. "Sound," Physics Classroom, Glenbrook South High School, Glenbrook, IL [accessed September 14, 2007] http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/soundtoc.html.
• Here you will find specific information on the physics of musical instruments like your bottle, which is an example of a closed-end air column:
  • Henderson, T., 2007b. "Musical Instruments: Closed-End Air Columns," Glenbrook South High School, Glenbrook, IL [accessed September 14, 2007] http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l5d.html.
• University of Virginia, date unknown. "Wavelength and Pitch: Musical Instruments," Physics Department, University of Virginia [accessed September 14, 2007] http://galileo.phys.virginia.edu/outreach/8thGradeSOL/WavePitchFrm.htm.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• Several clean glass bottles with narrow necks
  • Tip: it is helpful to have several bottles with the same size and shape, plus others with different size and shape.
• Water
• Electronic chromatic tuner (e.g., Korg CA-30, widely available in music stores and online)
• Ruler marked in centimeters
• Optional: piano or keyboard for comparing notes

Experimental Procedure

1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
2. Fill a bottle one-third of the way full with water.
3. Touch your lower lip to the edge of the bottle, purse your upper lip, and blow gently over the opening. When you get the airflow just right, you will hear a musical note as the air column in the open bottle resonates.
4. Use the chromatic tuner to see which musical note is sounding.
5. Add a little more water and blow again.
   1. How does the pitch of the note change? Is it higher or lower than before?
   2. Listen carefully and see if you can tell, then use the chromatic tuner to see which musical note is sounding.
6. Figure out how much water you need to add (or remove) to get a half-step change in pitch (e.g. from C to C-sharp, or from A to A-flat).
7. Using a series of identical bottles with different amounts of water, can you produce a series of notes in a musical scale? How do the water levels (or perhaps more importantly, the remaining empty air levels) change as the pitch of the note produced changes?
8. Repeat the experiment using bottles with different shapes. How is the pitch of the note produced related to the water level?

Variations

• What happens if instead of blowing over the top of the bottle, you tap the bottle (below the waterline) with a wooden mallet? How does the note produced by tapping change with water level in the bottle? Can you explain how this works?
• You can also make musical notes by rubbing the rim of a wine glass with a wet finger. With wine glasses, the note frequency also changes as the fluid level is increased, but in the opposite direction of the bottles used in this experiment. Obviously, the physics of musical wine glasses must be different! Find out more with the Science Buddies project Singing Wineglasses.

• For more science project ideas in this area of science, see Music Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

Last edit date: 2011-10-26 10:00:00