Air columns and pitch
Explore the relationship between water height in a tube and the musical note produced when blowing into it.
Activity Summary
Students explore fundamental concepts of music and acoustics using plastic tubes and water. They experiment with note pitch by adding water, identify notes with FizziQ Junior, and discover the link between air column length and sound frequency.
Introduction
Have you ever blown into an empty bottle to produce a deep, low sound? And did you notice that if you fill the bottle with water, the sound becomes higher-pitched? This phenomenon, easily observed in everyday life, is the basis for how many musical instruments work, like the flute, clarinet, or organ.
When you blow into a tube, the air inside starts vibrating and produces a sound. The pitch of this sound, meaning whether it's low or high, depends on the length of the vibrating air column. The longer this column, the lower the sound. The shorter it is, the higher the sound.
Musicians have known this relationship for millennia. In this activity, you will become a true scientific instrument maker: by adding water to tubes, you will modify the air column length and create precise notes of the musical scale. Thanks to FizziQ Junior tools, you can verify your results and discover how physics and music are intimately connected.
Learning Objectives
- Discover the relationship between air column length and produced sound pitch.
- Use the FizziQ Junior Notes measurement instrument to identify a musical note.
- Compare produced notes with those from the FizziQ Junior Flute synthesizer.
- Develop an experimental approach: hypothesis, measurement, analysis, conclusion.
- Document observations in the digital experiment notebook.
Scientific Concepts
Instruments and sensors
Scientific instruments
- Notes measurement instrument
Sensors
- Microphone
FizziQ Features
- Flute synthesizer — Produces reference notes so students can compare them by ear with the sound of each tube.
- Experiment notebook — Used to record water heights, photos of the tubes, and group conclusions throughout the session.
Required Materials
- - Smartphone or tablet with the FizziQ Junior app - 3 transparent plastic test tubes per group - A graduated ruler - A pipette or small container for pouring water - Water - Note: the protocol remains adaptable to any comparable sound/pitch analysis tool.
Experimental Protocol
Separate the class into groups of 3-4 students. Distribute to each group three transparent plastic tubes, a ruler, and a pipette with water.
Ask each student to gently blow into the open end of an empty tube to produce a sound. Help students position their mouth and breath if needed.
Open FizziQ Junior and access the Flute musical instrument. Specify that only white keys will be used, not semitones.
Ask students to compare the empty tube sound with Flute notes. Which note is closest? Students add this observation to the experiment notebook.
Ask them to add a little water to one of the tubes, then blow again. What happens? Has the note changed? Is it higher or lower?
Propose the following challenge: find the right water height to obtain exactly the next note in the scale (for example if the empty tube gave a D, obtain an E).
When the water amount corresponds to the target note, students measure the water height with the ruler, take a photo of the tube, and add everything to the experiment notebook.
Students repeat the exercise to obtain the following note in the scale and document their results in the notebook.
Have them reflect: how do you get higher or lower notes? Is the note very sensitive to water amount? Are water height intervals between two notes identical?
Pool results from all groups on the board. For each note, compare the water heights found. Are results consistent between groups?
Explain the principle of air column resonance: water reduces the available air column length, which increases frequency and makes the sound higher-pitched.
Choose a tube with a certain water height and ask groups to find three ways to identify the note: by ruler and calculation, by comparison with the Flute synthesizer, and by the Notes measurement instrument.
Present the FizziQ Junior Notes measurement instrument which analyzes sounds and automatically determines the played note. Let students use it for their different tubes.
Students document the entire session, their measurements, and conclusions in the FizziQ Junior experiment notebook.
Expected Results
Students will observe that an empty tube produces a low note and that by adding water, the sound becomes progressively higher-pitched. They will notice that to move from one note to the next in the scale, they need to add an approximately regular amount of water.
The FizziQ Junior Notes instrument will confirm the correspondence between produced sound and scale note. Differences between different groups' results are expected due to difficulty blowing perfectly regularly and dosing water precisely. The note's sensitivity to water amount will be noticed: a small change in water level noticeably modifies sound pitch.
Scientific Questions
- Why does the sound become higher-pitched when you add water to the tube?
- Does the produced note depend only on water height or also on tube diameter?
- Why is it difficult to get exactly the same note every time you blow?
- Can you create a complete scale with different-sized tubes without adding water?
- How do flute or organ makers use this principle to manufacture their instruments?
Scientific Background
Acoustics is the study of sounds, their production, transmission, and reception. Sounds are vibrations that propagate as mechanical waves through a material medium like air, water, or a solid. Each sound has three main characteristics that make it unique: frequency, intensity, and timbre.
Frequency corresponds to the number of vibrations per second of the sound wave. It is measured in hertz (Hz). The higher the frequency, the higher-pitched the sound. The lower it is, the lower-pitched the sound. The human ear can perceive sounds with frequencies between about 20 Hz and 20,000 Hz.
Musical notes are organized according to a system of specific frequencies called the musical scale. For example, the standard A note has a frequency of 440 Hz. An octave is a musical interval in which the upper note's frequency is exactly double that of the lower note. Thus, the A of the octave above has a frequency of 880 Hz.
When a student blows into a tube, they create a vibration of the air inside the tube. This vibration propagates as sound waves that are amplified by the tube's resonance. The air column length determines the frequency at which it resonates and therefore the pitch of the produced note.
When students add water to tubes, they reduce the air column length available for resonance. The shorter air column vibrates at a higher frequency, making the note higher-pitched. Conversely, by removing water, the air column lengthens and frequency decreases, making the sound lower-pitched.
This principle of air column resonance is the basis for many wind instruments: the flute, clarinet, oboe, trumpet, or organ all use air columns of different lengths to produce various notes.
Extensions
- Use bottles of different sizes instead of test tubes to explore lower sounds.
- Try to play a simple melody with several tubes tuned to successive notes.
- Compare notes obtained by blowing into the tube with those obtained by tapping the tube with a pencil.
- Measure the exact frequency with the Notes instrument and plot a graph of frequency vs. water height.
- Explore semitones by finely adjusting water amount.
Frequently Asked Questions
Some students can't produce a sound by blowing into the tube, what should I do?
You need to blow gently at an angle across the tube's edge, not directly into it. The technique is similar to blowing into a bottle. A little practice is usually enough.
Results vary a lot from one group to another, is this normal?
Yes, it's normal and it's an important pedagogical point. Breath strength, angle, and water filling precision all influence the result. It's an opportunity to discuss sources of experimental error.
Why doesn't the Notes instrument always recognize the correct note?
The Notes instrument analyzes the dominant frequency of the sound. If the breath is too weak, too strong, or irregular, the analysis can be disrupted. You need to blow steadily and regularly for at least one second.
Can you use other liquids than water?
Yes, but it won't change the produced note because it's the air column length that determines frequency, not the liquid's nature.
Detailed Description
Students explore fundamental concepts of music and acoustics using plastic tubes and water. In groups, they experiment with note pitch by adding or removing water from tubes, then identify the notes produced using the Notes measurement instrument and the Flute synthesizer in FizziQ Junior. They discover the link between air column length and the frequency of the produced sound. FizziQ Junior's Notes measurement instrument uses the smartphone's microphone to analyze the sound in real time and identify the played note, and students log their water-height measurements, photos, and conclusions in the app's experiment notebook.
This activity is part of our sound resources. To dig deeper into measuring and analyzing sound (waveform, spectrum, spectrogram, decibels) and find all twelve experiments, read our complete guide to measuring and analyzing sound with a smartphone or computer.
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