Originally Posted by Erin
Just a thought... but I understood the most effective jet-drive was when the jet was just above or partially above the water line and pointing down/at it. I thought that if the jet was totally submerged it wasn't as effective.
I think that you are right, but it's because a jet of water won't accelerate as much if going straight into water, whereas if it goes into air you get a bigger/better acceleration effect (Force = Mass x Acceleration) before it hits the water.
If you use a pressure washer to clean the car, it doesn't push back harder the closer you are to the car - the force all comes from the water coming out of the nozzle, not what it hits.
It's the same as the hosepipe into a bucket that Kitten mentioned earlier.