Quick answer: Sound is made by vibrations and travels through a medium such as air, water or steel, but not through a vacuum. This grade 6 science lab on sound waves gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
How does the length of an air column change the pitch of a note? In this lab you blow across a cylinder with different water levels and read the frequency with a phone. You look for a pattern and judge how reliable the readings are.
Level: Grade 6 science (Year 7 · Class 6) · Curriculum: MS-PS4-1
Aim
To find how the length of a column of air affects the pitch of the sound it makes when you blow across the top.
Equipment
- Tall plastic cylinder or clear tube about 3 cm wide and 30 cm tall
- Water and a jug
- Ruler
- Smartphone with a free frequency-analysis app
- Paper towels
Safety
Wipe up any spilled water at once so nobody slips. Blow gently and do not hold your breath, to avoid feeling dizzy, and keep the volume of sound moderate to protect your ears.
Method
- Pour water into the cylinder until the air column above it is 20 cm long, measured from the surface to the top rim.
- Blow gently across the top rim until you hear a clear note.
- Use the phone app to read the frequency of the note in hertz.
- Add water to shorten the air column to 16 cm, 12 cm, 8 cm and 4 cm, and repeat each time.
- Record the results in the table.
Results
Sample measurements:
| Air column L (cm) | 20 | 16 | 12 | 8 | 4 |
|---|---|---|---|---|---|
| Frequency (Hz) | 410 | 510 | 660 | 960 | 1750 |
Analysis questions
Question 1 Pattern
Describe how the frequency changes as the air column gets shorter.Question 2 Highest pitch
State the length of the air column that gave the highest pitch and the frequency.Question 3 Comparing two columns
Calculate how many times greater the frequency is for 8 cm than for 20 cm.Question 4 Graph
Plot frequency (vertical axis) against air column length (horizontal axis) and describe the shape.Question 5 Prediction
Predict whether a 24 cm air column would give a frequency above or below 410 Hz and explain.Question 6 What vibrates
State what vibrates to make the sound, and name two things to keep the same.Question 7 Uncertainty
The app reads to ±10 Hz. Calculate the percentage uncertainty for 410 Hz and for 1750 Hz.
