I tried posting this yesterday, but somehow, the message must have gone to "bit heaven".

Hasselblad (of all people) produced an excellent explanation of f/stops and shutter speeds by relating f/stops to pipe diameters and shutter speeds to time, with "exposure" being the amount of water that has flowed through. Excellent analogies, with the intensity of light related to water pressure. All in one slim "freebie" book.

Contact Hasselblad USA - I'm sure they'll help.