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Wave speed on a string depends on tension and linear mass density.
Sound is a compression-rarefaction wave; speed set by bulk modulus and density.
Sound travels fastest in solids, slower in liquids, slowest in gases.
Sound reflected back after ≥ 0.1 s is heard as an echo; sonar uses this to measure depth.
Loudness measured logarithmically — each 10 dB = 10× the intensity.
Two overlapping waves' displacements add — constructive or destructive interference.
A string fixed at both ends supports a discrete set of resonant modes.
Open pipes carry all harmonics, closed pipes only odd ones.
Two near-equal frequencies superpose to give a pulsing amplitude.
When driving frequency matches the natural one, amplitude grows sharply.