Why is it that when you put your finger over the tip of a hose the water shoots out farther?
Asked by: Sparrow
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
'The true spirit of delight, the exaltation, the sense of being more than Man, which is the touchstone of the highest excellence, is to be found in mathematics as surely as in poetry.'