dave
of couse the screw would work. it works in water(propeller) and a helicopter blade is basicaly a screw. aeroplane blades are often called screws.
helmet
i understand how you understand the consept of newtons law. i dont obviosly dont and also wont set my self to beleive in one mans rules. but it is inconclusive to me to say somthing stationairy is in equelibrium and something spinning is not.
eg. the tractor spining around the stump could be said to be in equelibrium if it doesnt move the stump. centrefugal=centripital(vorticy's law of phisics)