Investigating Pitch with Straw Pan Flutes
How Does Straw Length Change Pitch?
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How Does Straw Length Change Pitch?
Central question: how does the length of the air column in a straw affect the pitch we hear? Keep the opening tied to investigation, not just craft-making.
Learning goal
I can plan and carry out an investigation to find how straw length affects pitch.
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What words come to mind when you hear high and low pitch?
Use this to surface everyday ideas about sound before the investigation. Expect words such as loud, quiet, music, whistle, high, low; briefly steer students away from confusing pitch with volume.
What We Are Investigating
In this lesson, pitch is the sound we hear as high or low.
We will change one thing: the length of the straw.
Then we will listen for the pattern in pitch.
Emphasise the scientific skill: students are not only making an instrument; they are testing a relationship between variables.
Planning a Fair Test
A fair test changes one variable at a time.
Independent variable: straw length
Dependent variable: pitch heard
Keep the same: type of straw, how you blow, and open tops
If needed, model the language of variables. At KS3/A2 level, hearing pitch as higher/lower is enough; no need for frequency measurements unless the class is ready.
Making a Prediction
Before testing, scientists predict what they think will happen.
Prediction: shorter straws will make a higher pitch, and longer straws will make a lower pitch.
Link prediction to prior everyday experience with musical instruments or bottles if useful, but keep the stated prediction exact and simple.
Setting Up the Investigation
Cut straws to different lengths
Put them in order: shortest to longest
Tape them together
Leave the tops open for blowing
Students need a clear range of lengths so the pattern is easy to hear. Encourage neat ordering because it supports later comparison.
Conducting the Test
Blow across the top of each straw and listen carefully.
Test each straw in turn from shortest to longest. Compare each sound with the next one instead of trying to remember all at once.
A common issue is students blowing into the straw instead of across the top. Demonstrate the technique briefly if needed.
In this investigation, what do we change?
straw length
pitch heard
type of sound
order of straws
Checks the independent variable from the planning slides. Students may confuse what is changed with what is heard.
Plan the fair test
In this investigation, the independent variable is straw length. The dependent variable is the pitch heard. To keep it fair, use the same type of straw and the same way of blowing each time.
Echoes the wording from slides 3 to 6 and reinforces fair-test vocabulary in context.
What Pattern Should We Notice?
As the straw length increases, the pitch should get lower.
Shorter air column → higher pitch
Longer air column → lower pitch
This is the key causal relationship of the lesson. Keep the exact phrase 'air column' consistent from here on.
Why the Sound Changes
The sound comes from vibrating air inside the straw.
Short straws have a shorter air column, so the air vibrates faster and makes a higher pitch. Long straws have a longer air column, so the air vibrates slower and makes a lower pitch.
Keep the mechanism simple: faster vibration = higher pitch, slower vibration = lower pitch. Avoid overcomplicating with wave equations.
Observations and Results
If the shortest straws sound highest and the longest straws sound lowest, the results support the prediction.
What to observe
What the results mean
Which straw makes the highest pitch
Which straw makes the lowest pitch
Whether the change is gradual from one straw to the next
Students may describe pitch with their own words at first. Guide them towards 'higher' and 'lower' rather than 'louder' and 'quieter'.
Conclusion
This investigation shows a clear link between straw length and pitch.
Changing the length of the vibrating air column changes the sound: shorter gives higher pitch, longer gives lower pitch.
Land the central question clearly here. The conclusion should refer back to the investigation and to the evidence students heard.
Scientific Skills Used
planning a fair test
identifying variables
making a prediction
observing carefully
comparing results
drawing a conclusion
This slide resolves the lesson as a lab skill lesson, not only a sound lesson.
Which straw should make the highest pitch?
the longest straw
the shortest straw
the widest straw
the taped straw
Checks the core pattern before or after students discuss results. Distractors reflect likely attention slips or irrelevant features.
Explain the pattern
The sound comes from vibrating air inside the straw. A shorter air column vibrates faster and makes a higher pitch. A longer air column vibrates slower and makes a lower pitch.
Anchors the mechanism from slides 7 to 10 using the exact taught terms.
How did your results support the prediction?
Expected elements: students should mention hearing that shorter straws made higher sounds and longer straws made lower sounds, and that this matched or supported the prediction.
What is one thing you learned today?
Reflection only. Invite brief answers about the main idea or scientific skill learned.
What helped you understand pitch best?
Reflection only. Useful for identifying which part of the practical lesson supported understanding best.
What part of this investigation felt hardest?
Reflection only. Encourage honest answers about difficulty, such as blowing technique, using variables, or hearing the pattern.
Glossary
pitch - how high or low a sound is
investigation - a scientific test to find out something
fair test - a test where only one variable is changed
independent variable - the thing you choose to change
dependent variable - the thing you observe or measure
air column - the space of air inside the straw
vibration - a fast back-and-forth movement that makes sound
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