What Changes the Speed

Why it matters

Sound jogs at 331 m/s through freezing air and sprints closer to 350 on a hot afternoon. But squeeze the air to double pressure and it doesn't speed up at all. Air keeps strange rules.

The idea in plain words

The speed sheet for air. Tap the factors.

v ≈ 331 + 0.6 T (m/s)

Speed of sound at 22 °C?

≈ 344 m/s — the number every echo problem borrows

• factor ✓: temperature — +0.6 m/s per °C — the big lever
• factor ✓: humidity — moist air is LIGHTER than dry (H₂O beats N₂/O₂ at molecular weight) → slightly faster
• non-factor ✗: pressure — no effect at constant temperature — density compensates exactly
• non-factors ✗: amplitude/frequency — neither loudness nor pitch changes the speed — all notes of a song arrive together
• v = 331 + 0.6 × 22

Predict first

Which change speeds up sound in air?

v ≈ 331 + 0.6T. Hotter molecules relay the wave faster. Pressure raises density in exact proportion to its push — the two cancel. Loudness never touches speed.

• raising the temperature — correct
• raising the pressure at constant temperature
• shouting louder

What you do

Warm the day until sound holds at exactly 344 m/s, toggle the humidity for the bonus nudge — then sweep the pressure and catch it doing nothing.

Check yourself

All the instruments of an orchestra reach you in step because…

If pitch changed speed, back-row listeners would hear scrambled music. They don't.

Sound carries slightly BETTER on humid monsoon days because…

Water vapour (18 u) displaces heavier N₂ (28) and O₂ (32) — lighter medium, faster relay.

On a mountaintop (low pressure, −5 °C), sound is slower than at a warm beach mainly because of…

Cold is the culprit: 331 + 0.6(−5) ≈ 328 m/s. The thin air alone would change nothing.

• speed doesn't depend on frequency — every pitch travels equally fast — correct
• the conductor times them
• low notes leave earlier
• moist air is less dense — v rises — correct
• water droplets carry the sound
• it doesn't — humidity slows sound
• the temperature difference — pressure itself doesn't matter — correct
• the low pressure
• the altitude's gravity