Sound Wave Propagation

Sound is a LONGITUDINAL pressure wave — alternating compressions and rarefactions of the medium.

Speed in air at 20°C: v ≈ 343 m/s. In water: ~1500 m/s. In steel: ~5000 m/s.

Sound requires a MEDIUM — cannot propagate in vacuum (unlike EM waves).

Speed in fluid: v = √(B/ρ), with B = bulk modulus, ρ = density.

In gas: v = √(γRT/M) — depends on T (not P or ρ separately).

Speed of sound rises ~0.6 m/s per °C in air. Doubling T (Kelvin) increases v by √2.

Audible range: 20 Hz - 20 kHz. Below: infrasound. Above: ultrasound.

Sound intensity: power per unit area, measured in W/m² or in decibels (logarithmic).