Sound Speed in Media

Sound speed depends on the MEDIUM. Generally: solid > liquid > gas.

Air at 20°C: ~343 m/s. Water: ~1500 m/s. Steel: ~5000 m/s. Glass: ~5000 m/s. Rubber: ~60 m/s.

Speed in a medium: v = √(B/ρ) for fluids, √(Y/ρ) for thin rod in solid, √(γP/ρ) for ideal gas.

Sound in solids can be longitudinal OR transverse (shear). Sound in fluids only longitudinal.

In gas: v ∝ √T (Kelvin), independent of pressure. Air at 0°C: 331 m/s.

Diatomic gas (air ~80% N₂): γ = 1.4. Monatomic (helium): γ = 5/3.

Sound speed in helium is 3× that in air at same T (lighter gas, lower M) — high-pitched 'Donald Duck' voice.

Underwater communication uses sound because water's slow attenuation (vs radio waves).