Why does the stream of water travel farther when less water is flowing from the end of the hose?

Answer 1

When using a high pressure pump, you'll find that a smaller output nozzle gives *shorter* spray than a large nozzle. Small nozzles limit the flow. Yet with a garden hose things are reversed. Why?

It's because the long narrow hose and the pipes connecting it are acting like "friction." If you turn on the water, the hose rubs against the wate, and water flows relatively slowly out the end of the hose. Also, the water pressure at the open end of the hose is very low.

Now install a garden sprayer at the hose end. This will greatly slow down the water flow, and the effect of friction is greatly reduced. The pressure at the far end of the hose rises, and this high pressure can create a very long (but narrow) spray.

Another way to explain is with numbers. The greater the fluid resistance is to a constant flow, the greater the pressure-difference must be across that resistance. The fluid resistance value of the hose is large, while the resistance value of the hose-end is small, and since the same flow goes through both the hose and through its end-opening, most of the pressure-difference appears along the hose, while very little pressure-difference appears between the

hose and its opening. Now install a very narrow opening. If the fluid resistance of this nozzle is the same as the fluid resistance of the hose, then half of the faucet pressure appears along the hose, while the other half appears between the hose-end and the outside world. The nozzle has increased the pressure at the hose end. And if the fluid resistance value of the nozzle is much greater than that of the hose, then nearly all of the faucet pressure will appear at the nozzle.

So, to produce a long jet of water, use a very wide hose and a very narrow nozzle. Or even better, entirely get rid of the resistance created by the hose, and connect the nozzle directly to a high pressure water pump.