what causes static

[chelyar]

what causes static

[ll_billym]

What type of static do you mean?

[gen2]

Any electrical discharge produces broad specrum radio waves.

(Actually one of Marconi's early radios utilised this effect in a device known as a Spark Transmitter)

All over the world there is everything from large electrical discharges taking place (lightning) down to the millions of tiny sparks produced in internal combustion engines.

This random background radio interference is known as STATIC and approximates to White Noise.

[strange452]

If you mean 'static' (as in the little shocks you get when you touch metal door handles etc) then this is caused by a build up of electric charge on you or another object. Simplistically, this is due to the rubbing of atoms/molecules against each other generating the charge (even "rubbing" against the air can build up a charge). If you are on an insulating surface the charge cannot dissipate so just increases in strength. If you then touch a conductor (eg. metal filing cabinet, car door etc) which is earthed, the charge will ground and you may feel that distinctive tingle (or pain!). You can build up quite a large potential in this way but usually at low power so it's not particularly dangerous. If you can see the discharge spark then you may have built up a potential of around 20kV ! You may also have noticed that the shocks seems to happen more frequently in the summer in dry periods. This is because air conductivity increases with humidity (the water is conductive) so tends to "bleed" accumulated charges away slowly. Obviously if the air is very dry the charge cannot bleed so builds up until a handy conductor appears. I'm not a scientist so most of this is from memory, but hope it helps.

[strange452]

Gen2's answer reminded me of an interesting piece of trivia. If anyone asks you how far you can see, tell them you can see about 13 billion light years without a telescope! (useful bet for a pint :-)), If you select an untuned channel on a TV, you will get "white noise" as Gen2 said. Most of the noise is terrestrial but about 3% is a result of the Cosmic Background Radiation (the radiation freed after the Big Bang when matter decoupled from radiation). As its' taken about 13 billion years to get here it must have travelled 13 billion light years!