Measuring the Speed of Sound – Smartphone Apps vs Classic Experiments
Sound is everywhere — but how fast does it really travel? In class, we explore different ways to measure the speed of sound, from modern smartphone apps to traditional tuning fork experiments.
📱 Using a Smartphone
Several apps can generate sounds and measure the time it takes for echoes to return. Students clap, whistle, or tap, and the app calculates the delay between the sound and its echo. With a known distance, it gives a speed of sound value — quick, simple, and surprisingly effective.
🎼 The Tuning Fork and Resonance Tube
For a more hands-on method, we use a tuning fork, a resonance tube, and a plunger.
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Strike the tuning fork and hold it over the tube.
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Adjust the plunger until the sound is loudest (a resonance point).
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Measure the length of air column at that resonance.
At the first loud point, the tube length corresponds to a quarter of a wavelength. With the tuning fork’s frequency known, students can calculate speed using:
By finding multiple harmonics, they refine the value. This method usually gives the most accurate result in the classroom.
🌊 What About Water and Solids?
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In Water: Use a pair of waterproof microphones (hydrophones) or speakers at a known distance apart. Send a pulse and measure the time difference. Sound travels about 1,500 m/s in water.
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In Solids: Tap one end of a metal rod or beam, and detect vibrations at the other end with sensors. Alternatively, use PASCO sonic sensors or accelerometers. Speeds in solids are even higher — steel carries sound at around 5,000 m/s.
🎓 Why This Works in Teaching
Students love comparing methods — the smartphone app feels modern and accessible, while the tuning fork experiment shows the physics in action. Extending the discussion to water and solids connects the classroom to sonar, ultrasound, and earthquake waves, showing how sound science underpins real-world technology.
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