Physics 2 — Momentum & Waves

Waves

continues from lesson 3 — values defined earlier in the course stay live here

wave anatomy — amplitude A, wavelength λ, crest and trough

Every wave obeys one bookkeeping rule: v = f·λ. Speed is set by the medium, frequency by the source — so wavelength is what adjusts. Sound in air:

v_{sound} := 343 m/s

= 343 m / s speed of sound, room temperature

f_{A4} := 440 Hz

= 440 Hz concert pitch A

\lambda_{A} = \frac{v_{sound}}{f_{A4}}

= 0.77955 m about 78 cm crest to crest

A guitar string only sustains waves that fit — whole numbers of half-wavelengths. Those are the harmonics, and they are why a string has a pitch at all:

L_{string} := 0.65 m

= 0.65 m scale length

v_{string} := 430 m/s

= 430 m / s wave speed on the string (tension & gauge set this)

f_{1} = \frac{v_{string}}{2 \cdot L_{string}}

= 330.77 Hz fundamental — about E₃ on a guitar

f_{2} = 2 \cdot f_{1}

= 661.54 Hz second harmonic: the octave

Where next: Electricity 2 treats AC as a wave — same f and λ thinking, now with volts.