People often use the term 'static' or 'static noise' to describe the sound of an untuned radio – which is more accuractely called white/pink/brown noise depending on the frequencies present.
I'm curious as to why it's called 'static'. What's unchanging?
From wikipedia all I could see was:
Alternatively, the use of an FM radio tuned to unused frequencies ("static") is a simpler and more cost-effective source of white noise
Best Answer
The Wikipedia article is, um, not as technically correct as it could be.
FM interstation hiss should not be called static. FM interstation hiss is not really accurate white noise (equal power at all frequencies) either, although it comes close.
True "static" wrt radio reception usually does not happen on FM, at all. (It can, if the source of the interference is extremely strong, or if the FM receiver's "AM rejection ratio" is poor, but this is uncommon.) It happens on AM.
It is indeed caused by discharges of static electricity - hence the name - mostly in the upper atmosphere. This noise was called "static" long before Edwin Howard Armstrong developed FM radio, in a successful quest to vanquish the noise.
The term is apt: If you tune an AM radio to an unused frequency, and then shuffle across the floor and touch a doorknob - or separate two dissimilar fabrics, fresh from the dryer, from each other - or pet a cat - ideally all in cold dry weather - you will produce static discharges (some big enough to see and feel as sparks), and you will hear pops and clicks in the radio speaker that are exactly like the rest of the "static" you hear on AM, except in intensity.
( Heck, Heinrich Hertz first created the first (known) human-generated radio waves in exactly this manner, by making sparks. I say "known" because people have obviously been making static discharges for forever, but we didn't know they produced electromagnetic waves - radio waves - until then. "Spark-gap" transmitters were all we had until rotary alternators came along. (Tesla's patents that are supposedly for "inventing radio" concern the rotary alternator, which was later improved on by Alexanderson.) )
So - why is FM interstation hiss called "static"? In technically correct usage, it isn't. In common use, though, when FM came along, people didn't distinguish between the hiss heard on an untuned FM receiver and the "static" pops and clicks from AM. They just knew that the latter had been called "static", and so in popular usage this was generalized to "noise from a radio receiver (and, later, TV receivers) when tuned to a weak or no station".