Sound cannot travel through nothing at all — it needs a medium to vibrate through. And two separate properties of a wave, frequency and amplitude, decide two completely different things about what you hear.
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Every sound starts with a vibration — and that vibration needs a medium (solid, liquid or gas) to travel through to reach your ear.
📌 How sound travels
A vibrating object disturbs the particles of the medium around it.
The disturbance passes from particle to particle as a wave — the particles themselves do not travel far, only the disturbance does.
No medium, no sound: sound cannot travel through a vacuum, which is why there is total silence in outer space.
📊 Speed of sound by medium
| Medium | Relative speed |
|---|---|
| Solids | Fastest — particles are closely packed |
| Liquids | Faster than gases, slower than solids |
| Gases (like air) | Slowest of the three |
These four words are often mixed up — but frequency and amplitude are properties of the wave, while pitch and loudness are what you actually perceive.
📊 Cause and the effect you hear
| Wave property | What it controls | Higher value means |
|---|---|---|
| Frequency (Hz) | Pitch | Higher-pitched sound (shriller) |
| Amplitude | Loudness | Louder sound |
Olympiad trap: A LOUD sound is not necessarily HIGH-pitched, and a SOFT sound is not necessarily LOW-pitched. A deep drum can be very loud (large amplitude) while staying low-pitched (low frequency).
The human ear cannot hear every frequency — and other animals hear ranges we cannot.
✨ The audible range
Human hearing range
20 Hz to 20,000 Hz
Below 20 Hz is infrasonic; above 20,000 Hz is ultrasonic.
Ultrasound uses
above human hearing
Bats use ultrasound to navigate; doctors use it for medical scans.
Pro tip: Noise pollution is measured in decibels (dB) — prolonged exposure above about 85 dB (like heavy traffic) can damage hearing, which is why continuous loud sound, not just a single loud moment, is the real danger.
12 NSO-pattern questions on sound and acoustic phenomena, including two Achievers-level questions.
