>>>>>
>>>>>
>>>>>What is it that revolves on the roof of a police car?
>>>>
>>>>Nothing.
>>>
>>>How so? What about when the cruiser's blue and red lights are on>
>>
>>On american police cars everything is fixed to the roof and nothing revolves on the roof.
>
>So how do the lights describe a circle?

They probably say "it's a curved line where all the points are at the same distance from a central point"... but nobody knows the light language, so this is under some serious doubt.