i am looking for a formula or text containing information on how to calculate the change in pressure when air is funneled, in a closed system, where the air is being forced through the system initially with no motion then forced through a pipe that has the same diameter for a relatively long distance then is suddenly funneled down to a much smaller diameter. any help is much appreciated. i can't seem to find anything related to this topic. most formulas i have found deal only with incompressible fluids where i am interested in air which, of course, can be compressed. thanks for any help.