Question from watching a water fountain today

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Discussion Overview

The discussion revolves around the physical principles governing the behavior of water in a fountain, particularly why the water spreads out in a wide pattern as it reaches the top. Participants explore concepts related to fluid dynamics, including potential connections to Bernoulli's equation and projectile motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant wonders if the spread of water at the top of the fountain is related to Bernoulli's equation, suggesting that factors like pipe diameter and water pressure may influence the height and spread of the water.
  • Another participant notes that as water rises, it cannot fall straight down due to the continuous flow, implying that it gains an initial horizontal velocity that could be modeled as projectile motion.
  • A participant questions why the stream of water appears to widen as it ascends, indicating a need for further explanation on this observation.
  • One participant offers a hypothesis involving the behavior of water molecules, suggesting that glancing collisions among them impart sideways momentum, causing the stream to spread as it rises.

Areas of Agreement / Disagreement

Participants express various viewpoints on the mechanics of water flow in fountains, with some agreeing on the influence of initial velocity and momentum, while others raise questions about the widening of the stream. The discussion remains unresolved with multiple competing ideas presented.

Contextual Notes

Some assumptions about fluid dynamics and the behavior of water molecules are not fully explored, and the discussion does not reach a consensus on the specific mechanisms at play.

curt2121
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so i was watchign a water fountain during a rally here today and was watchign the fountain in the middle and was wondering why (physically) when the water reaches the top it begins fallign in such a wide pattern. it makes sense to me intuitively but i don't know enough about physics to know just how it works. is it related to bernoulli's equation somehow? THat was my only thought when seeing it that maybe the spread of the water at the top can depend on the diameter of the pipe emitting the water and the pressure with which the water is pumped (and therefore the height it reaches) does any of that make sense? Am i even close to understanding just how this works? I guess that week off made my brain want to be used again so I'm pretty curious now. thanks!
 
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well obviously it can't fall downwards as more water is coming from there so it must be pushed outwards somewhat as it moves past the water moving up. this gives it a certain initial horizontal velocity which sort of makes it behave like a projectile, or at least you could do a rough model of the motion of those droplets using those equations
 
well yes that part is true, but the stream of water seemed to get wider as the height increased. why is that?
 
I've often wondered how a stream of urine initiates and maintains a uniform flow. No kidding!
 
If you start at the origin and roll a ball bunch of balls, one after another, in the x-direction, and then nudge each one in the y-direction a little once it reaches x=5, then the balls farthest from the x-axis will also be the ones farthest from the y-axis. My guess is that the water molecules in the stream don't go exactly straight up, so they undergo glancing collisions with other molecules in the stream, and this gives them a sideways nudge. This nudge gives them sideways momentum, and as they carry on upwards, this momentum carries them farther from the center of the stream as well. So the molecules that are higher up have been in the air longer, and hence have had sideways momentum for a longer time, and hence are further out to the side. That's my guess.
 
Loren Booda said:
I've often wondered how a stream of urine initiates and maintains a uniform flow. No kidding!

If you're my age it doesn't. I went to a u/r doc last year about my prostate and he said it wasn't that, but rather "mucus in the urethra". He offered no help. Not all the guys who leave spots and puddles in the men's room are doing it deliberately. Would you believe sideways? Yep, a real right angle.
 
FunkyDwarf said:
as for the urine the penis is built like a gun barrel with spirals to keep it going straight :)

Everybody's? Rats! I thought I was special.
 

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