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Question

Why is it that when you put your finger over the tip of a hose the water shoots out farther?
Asked by: Sparrow

Answer

The answer centers on the idea of matter conservation. If a certain amount of water flows into the hose from the spigot, that water must either flow out of the hose at the other end, or accumulate inside the hose itself. Since a garden hose is made of stiff plastic (generally), it won't expand to let more water accumulate, so the water must eventually flow out of the end of the hose. When you put your finger over the tip of the hose, you decrease the amount of space the water has to flow through. Since the same amount of water has to flow out of the hose before and after you place you finger over the end, the water must shoot out faster (to keep the amount of water flowing out a constant). And, thus, since the water shoots out faster, it travels farther. To find further information about this, I would suggest any basic physics textbook, or, more in-depth, a textbook on fluid mechanics.
Answered by: Andreas Birkedal-Hansen, M.A., Physics Grad Student, UC Berkeley


When the hose is off, water is being pushed against the valve at a constant pressure (measured in force per unit area, like psi or Newtons per square meter). Therefore force on the water is equal to pressure x area. When the hose is turned on, water will be released, and will go a distance depending on this pressure and the opening area of the hose. If you put your finger partway over the hose, there is less area for the water to come out, and therefore the force is greater.
Answered by: Andy T, Engineering Undergraduate, U. of Toronto


Science Quote

'A theory with mathematical beauty is more likely to be correct than an ugly one that fits some experimental data. God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.'

Paul Dirac
(1902-1984)


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