How Heat Sings

Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★★ Requires a more experienced teacher
Safety: ★★☆ Some safety precautions required to perform safely

Categories: Sound

Alternative titles: A Hot Tone

Summary

When a PVC pipe is placed over a propane torch flame, the heated air resonates within the tube, producing a tone. The pitch depends on the length of the pipe, with longer tubes producing lower tones.

Procedure

Light a propane torch and set it to its hottest setting.
Position the flame so that it points horizontally.
Lower a PVC pipe vertically over the flame, adjusting its height until a resonant tone is heard.

Links

How Heat Sings (Thermoacoustic Resonance) - Walter Lewin:

📄 A Hot Tone - Lucas Owens (Page 11 - A Hot Tone): https://www.unco.edu/nhs/science/pdf/demos/2013_LongsPeak.pdf

Variations

Use pipes of varying diameters to observe changes in resonance.

Safety Precautions

Always wear heat-resistant gloves and safety glasses when working with open flames.
Keep flammable materials away from the flame.
Hold the torch securely and never point it toward yourself or others.
Ensure the work area is well-ventilated to avoid buildup of combustion gases.
Allow pipes to cool before handling after use.

Questions to Consider

Why does heated air create a standing wave in the tube?
How does the length of the tube affect the frequency of the sound produced?