Acoustic physics: sound you can see

Sound made visible and audible. Sand dances into Chladni figures on a vibrating plate, eight strings show the harmonic series as standing waves you can pluck and hear, and an oscilloscope draws the Lissajous figure of each musical interval.

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What you can explore

Cymatics

A square plate vibrates in one of its natural modes and sand gathers along the nodal lines, where the plate stays still. Tap a tone pad to change the mode and hear its frequency.

Harmonics

Eight strings vibrate in the first eight harmonics of the same fundamental. Pluck one to hear it, and count the nodes: the nth harmonic has n − 1 of them between the ends.

Lissajous

An oscilloscope in X–Y mode traces two sine waves against each other. Simple frequency ratios such as 1:2 and 2:3 give stable closed figures, which is why those intervals sound consonant.

Key equations

  • fₙ = n f₀
  • λₙ = 2L / n
  • x = sin(at), y = sin(bt + δ)

Curriculum

AQA A-level physics 3.3.1, IB Physics C.4.

Common questions

What are Chladni figures?

Patterns formed when sand on a vibrating plate collects along the nodal lines, the places that do not move in that mode of vibration.

What is the harmonic series?

The set of frequencies f₀, 2f₀, 3f₀ and so on at which a string fixed at both ends can vibrate. Together they give an instrument its timbre.

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