Revise: Effects and Characteristics of Sound

v = 331+0.6T — sound needs a medium, cannot travel through a vacuum.

T=20°C → v=343 m/s.

d = vt/2 — divide by 2 for the round trip.

v=340,t=0.6s → d=102m.

Human range: 20Hz–20kHz. d_min=(v×0.1)/2.

In air: d_min=17m.

f' = f(v±v₀)/(v∓v_s). Approaching: higher pitch.

f=500Hz, source approaching at 20m/s → f'≈531Hz.

v = fλ.

v=340,f=170Hz → λ=2m.

Fastest in solids, slower in liquids, slowest in gases.

Pressing an ear to a wall hears sound more clearly.

Sonar and radar use the same round-trip timing principle.

Ships use sonar to measure ocean depth.

Below d_min, reflected sound blends into the original.

Small rooms produce reverberation, not distinct echoes.

Caused by wave crests crowding together or spreading apart.

An ambulance siren drops in pitch right after passing.

Amplitude (loudness) is independent of wavelength/frequency (pitch).

Bass notes need larger speakers for their long wavelengths.