Can Three Holes in a Tall Cylinder of Water Create a Hydrodynamic Coincidence?

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In a tall cylinder filled with water, it is impossible to create three holes that produce water streams intersecting at a single point. The analysis involves using Bernoulli's law to derive the trajectories of the water streams from each hole. The equations show that for two holes at different heights to intersect, the third hole must be at the same height as one of the first two. This conclusion indicates that three distinct holes cannot share a common intersection point for their streams. Alternative configurations, such as a conical container, may allow for different outcomes but deviate from the original question's parameters.
Loren Booda
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Given a comparatively tall cylinder full of water, is it possible to punch in its side three similar holes so that their streams all intersect at one point?
 
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I think it is not possible!

In order to find if there is an intersection point we have to find the equations that describe the trajectories of its stream of water and demand that they have a common point.
Thus let one hole to live at height h from the ground while the surface of the water in the cylinder lives at height H (at some instance of time). Furthermore we assume that the velocity of the surface is negligible with respect to the velocity of the water leaving from the hole. Then from Bernoulli's law we have

\rho\,g\,H=\frac{1}{2}\,\rho\,v^2+\rho\,g\,h\Rightarrow v^2=2\,g\,(H-h)​

When the water leaves the hole it feels only its weight, so the equations of motion are


\left\{\begin{array}{l}x=v\cdot t\\ y=h-\frac{1}{2}\,g\,t^2\end{array}\Rightarrow y=h-\frac{g}{2\,v^2}\,x^2\Rightarrow y=h-\frac{x^2}{4\,(H-h)} \quad (1)

I choosed my coordinate system having its origin at the bottom corner of the cylinder, right below the holes.
Now take the first two holes living at heights h_1,\,h_2 respectively. In order the trajectories to have a common point they must both fulfill equation (1) for some coordinates (x_o>0,y_o>0), i.e.


\left{\begin{array}{l} y_o=h_1-\frac{x_o^2}{4\,(H-h_1)}\\y_o=h_2-\frac{x_o^2}{4\,(H-h_2)}\end{array}\Rightarrow \left\{\begin{array}{l}x_o=2\,\sqrt{(H-h_1)(H-h_2)} \\ y_o=h_1+h_2-H \end{array}

Now for the 3rd hole in height h_3 equation (1) merely defines h_3 if we plug in it the above values of (x_o,y_o). Thus we arrive to


y_o=h_3-\frac{x_o^2}{4\,(H-h_3)}\Rightarrow \frac{(h_3-h_1)(h_3-h_2)}{H-h_3}=0\Rightarrow h_3=h_1 \quad \text{or} \quad h_3=h_2

Thus the 3rd hole must be identified with the 1st or the 2nd hole, which means that we can't have three holes with a common intersetion point for their streams.
 
Rainbow Child,

Solved like a true physicist!
 
Very nice :biggrin:

Could you achieve the 'three-point intersection' with a conical container though?
 
Yes, but only by nit-picking your question way beyond your intention.
 
For example, he never said the cylinder had to be oriented vertically...
 
TVP45 said:
Yes, but only by nit-picking your question way beyond your intention.

Sorry, I messed up the quote feature again. I was replying to the OP, not dst.
 
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