Assertion: fire engine's siren | /r/MadeOf | rotating disk
Facets:
value: with holes in it
type: OTHER
Source sentences:
text: The pneumatic siren, which is a free aerophone, consists of a rotating disk with holes in it (called a chopper, siren disk or rotor), such that the material between the holes interrupts a flow of air from fixed holes on the outside of the unit (called a stator).