Doppler

why sirens fall when they pass you.

drag the car — watch its waves bunch and stretch

A moving sound source doesn’t actually change its own pitch, but a listener hears it that way because the source’s wavefronts get compressed in front of it and stretched out behind it. That’s why a siren sounds higher as it approaches and drops the moment it passes you and starts pulling away.

Concepts: sound, waves.

An interactive you play with one thumb, on Wundr.