When I was young, a fun chore was watering the grass or any other job that involved using the garden hose. The heavy brass adjustable nozzle could focus a beam of water that gave the definite feel of jet engine or rocket thrust when held loosely in hand. This thrust could be played with even further by bending the hose to point down and holding it several feet away from the nozzle, and delicately balancing the hose extended out horizontally and supported by the nozzle thrust. By adjusting the faucet setting up and down the effect on the nozzle thrust was cleanly obvious. It made a great rocket toy, performing take-offs and backwards landings with faucet adjustments. As I grew up a little this nozzle thrust lost some of fascination, but I also noticed another strange phenomenon associated with hose nozzle thrust that held my attention all my adult life. If I held the nozzle in the normal way, pointed down, the thrust was noticeable to my sense of touch as I shortened the distance between the nozzle and the ground UNTIL a certain short distance was reached. This magical distance is about a quarter of an inch, or several millimeters. At this very short distance the thrust suddenly disappears and a sudden reverse thrust appears. It’s an odd sensation, as if the ground is attracting the nozzle, and strongly too! It not only overcomes the thrust force, but there’s an additional force easily felt directed downward. This sudden attractive force baffled me for years. As learned more science, it roughly resembled nuclear physics, where the electrical repulsion of two protons is suddenly overcome by the binding attractive Strong Nuclear Force. I even wondered if the mechanisms of water flow could guide an understanding of the nucleus. I asked many people about it and no one could explain how the water flow could caused this strange, sudden attraction at short distances. It seems few had ever even experienced it, since the short distance required to feel it means getting a little wet. Then one day a friend who operated a power-spray hydro-blasting business and I were hosing off his driveway and I asked him about it. In one minute he had a theory. Testing it took us one more minute, and in a total of two minutes a life long mystery was suddenly, and conclusively SOLVED! It's worth trying this out for yourselves, to feel this strange anti-thrust force that only appears when the nozzle gets very close to the ground. After getting your feet wet, see if you tell me (1) what was his theory, and (2) what was the definitive test?
I'll bet in the case of thrust away from the ground, the force is being caused by pressurized water being forced to squeeze its way down the hose. When you put the hose near the ground, I'll bet a lot of the water gets trapped and sends a pressure wave back up the hose going the other way, pushing the hose down towards the ground. A test of that might be to play with the power setting on the hose and the amount you squeeze it to adjust the pressure.
This post is intriguing but alas all of my hoses are buried in snow. I think sufficient time has passed for you to elaborate, MikeO Please Register or Log in to view the hidden image!
