Wavelength × Frequency (Mechanical)

Fundamental wave relation: v = f·λ, true for ALL waves (mechanical and EM).

Wavelength λ: spatial period — distance between consecutive crests (or any equivalent points).

Frequency f: temporal period — number of full waves passing per second. Period T = 1/f.

Angular frequency ω = 2πf. Wave number k = 2π/λ.

Speed: v = ω/k = fλ. Depends on the medium (for mechanical waves) or fundamental constants (for EM in vacuum).

In a given medium, f is set by the source; λ adjusts.

When the wave crosses media, v changes, λ changes, f stays the same.

Audible sound: 20 Hz - 20 kHz, λ = 17 m down to 1.7 cm in air.