Question 1

Why does sound travel faster in solids than in air?

Accepted Answer

Sound speed depends on the medium's stiffness and density: v = √(modulus/density). Solids have much higher stiffness (they resist compression more strongly), which dominates over their higher density. In steel, sound travels at 5,960 m/s versus 343 m/s in air. This is why you can hear a train coming by putting your ear on the rail before hearing it through air.

Question 2

Why can't sound travel through space?

Accepted Answer

Sound is a mechanical wave that needs a medium (matter) to propagate—it travels through compression and rarefaction of atoms/molecules. Space is a near-perfect vacuum with too few particles to transmit these compressions. Electromagnetic waves (light, radio) are oscillations of electric and magnetic fields, which don't require matter, so they travel fine through space.

Question 3

How do noise-canceling headphones work?

Accepted Answer

They use destructive interference. A microphone picks up ambient noise, and electronics generate a sound wave with the same frequency but inverted (180° out of phase). When this anti-noise wave combines with the original noise, peaks align with troughs and they cancel out. This works best for steady, low-frequency sounds like airplane engine hum.

Question 4

Why does my voice sound different on recordings?

Accepted Answer

When you speak, you hear your voice two ways: through air (like others hear it) and through bone conduction (vibrations through your skull). Bone conduction emphasizes lower frequencies, making your voice sound deeper to yourself. Recordings capture only the air-conducted sound, so it sounds higher and 'thinner' than what you're used to hearing internally.

Question 5

What causes the Doppler effect?

Accepted Answer

When a wave source moves toward you, each successive wave crest is emitted from a position closer to you, effectively compressing the wavelengths and increasing the frequency you perceive. Moving away stretches wavelengths, decreasing frequency. This is why an ambulance siren sounds higher pitched approaching and lower pitched receding. The effect works for all waves, including light (redshift/blueshift).

Question 6

How can an opera singer shatter a glass with their voice?

Accepted Answer

Every object has natural resonant frequencies. If you drive an object at its resonant frequency, energy accumulates and amplitude grows dramatically. A crystal wine glass has a specific resonant frequency. If a singer (or speaker) produces that exact frequency at sufficient volume, the glass vibrates more and more intensely until the stress exceeds the glass's strength and it shatters. This requires precise pitch and high volume.

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