Sound Waves
Year 7 🌊 Waves & Optics Describe how sound travels; relate pitch to frequency and loudness to amplitude.
🔊 How Sound is Produced
Sound is produced by vibrating objects. These vibrations travel through a medium as a longitudinal wave — particles vibrate back and forth in the same direction the wave travels.
🥁 Drum: The drum skin vibrates → pushes air particles together (compression) → particles pull apart (rarefaction) → wave travels outward.
Sound cannot travel through a vacuum — there are no particles to vibrate! In space, no one can hear you scream. 😱
| 🌍 Medium | 🏃 Speed of sound |
|---|---|
| Air (20°C) | ≈ 340 m/s |
| Water | ≈ 1500 m/s |
| Steel | ≈ 5000 m/s |
| Vacuum | 0 m/s (cannot travel!) |
🎵 Pitch and Loudness
Pitch (how high or low a sound sounds) depends on frequency. Loudness depends on amplitude.
| 🔊 Property | 📊 Depends on | 📏 Unit |
|---|---|---|
| Pitch | Frequency (f) | Hertz (Hz) |
| Loudness | Amplitude (A) | Decibels (dB) |
🎸 Guitar string: Tighter string → higher frequency → higher pitch. Pluck harder → bigger amplitude → louder sound.
🌊 Wave Equation
$$v = f\lambda \qquad T = \frac{1}{f}$$🧪 Properties of Sound Waves
Sound waves show all wave properties: reflection (echoes), refraction, and diffraction.
🏔️ Echo: Sound reflects off a cliff. If the cliff is 170 m away, the echo returns after 2 × 170 ÷ 340 = 1 second.
Bats use ultrasound (above 20,000 Hz) to navigate and hunt — they listen for echoes from their squeaks bouncing off objects!
👂 Human hearing range: 20 Hz to 20,000 Hz. Low bass sounds are ~50 Hz; high notes can reach ~4000 Hz.
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
🔊 Sound Wave Calculator
💡 Speed of sound in air ≈ 340 m/s at 20°C