Faucet Physics Question

[Lazymeatball]

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balls are not fluid.

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and that is the reason why they were a useful example.

[MelchyBeau]

water is attracted to itself. amazing I know. water is also attracted to edges. so there is going to be water falling from the edge of the faucet. but as it falls, it becomes attracted to the other water, thus it meets.

Melch (wacki isn't the only scientist on these forums)

[wacki]

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(wacki isn't the only scientist on these forums)


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Cool, what specialty are you in?

[Patrick del Poker Grande]

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water is attracted to itself. amazing I know. water is also attracted to edges. so there is going to be water falling from the edge of the faucet. but as it falls, it becomes attracted to the other water, thus it meets.

Melch (wacki isn't the only scientist on these forums)

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I'm going to go with this one as being closest to the actual answer.

[ThaSaltCracka]

[BeerMoney]

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water is attracted to itself. amazing I know. water is also attracted to edges. so there is going to be water falling from the edge of the faucet. but as it falls, it becomes attracted to the other water, thus it meets.



Melch (wacki isn't the only scientist on these forums)

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I'm going to go with this one as being closest to the actual answer.

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I would agree with this too.. Also note that when water comes out of the faucet it passes through an aerator.. This is what i think makes it wider at the top to begin with. Notice that if you saw water coming out of an open pipe or a hose, i don't think this same phenomenon occurs.

[Sweaburg]

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[ QUOTE ]
[ QUOTE ]
water is attracted to itself. amazing I know. water is also attracted to edges. so there is going to be water falling from the edge of the faucet. but as it falls, it becomes attracted to the other water, thus it meets.



Melch (wacki isn't the only scientist on these forums)

[/ QUOTE ]
I'm going to go with this one as being closest to the actual answer.

[/ QUOTE ]

I would agree with this too.. Also note that when water comes out of the faucet it passes through an aerator.. This is what i think makes it wider at the top to begin with. Notice that if you saw water coming out of an open pipe or a hose, i don't think this same phenomenon occurs.

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That aerator idea sounded good but I just took the aerator off my faucet and saw the same effect.(I know I know, turn down the nerd but this is more interesting than the research I am doing)

Also if the water is attracted (ie wants to stick) to the edges of the tap wouldn't that mean less water flowing from the edges?

Does it have anything to do with the velocity profile across the stream? The water in the middle of the faucet is travelling faster if I remember correctly.

[InchoateHand]

straight.

[The Goober]

This has essentially already been said, but I'll take a shot at explaining this...

Everyone agrees that for a steady stream of water or sand or anything else, the mass / unit time passing through any plane of the stream (the flux) has to be equal - this is the conservation of mass part, and is essential. The flux for any cross-section of the stream is equal to Area x Velocity x Density. Since the velocity increases further down the stream, the area and/or the density must decrease to compensate. Since the stream is a unbroken column of water, the density cannot decrease (because its a liquid) and so the cross-sectional area must decrease. In the sand case, the individual grains of sand act sort of like a gas, so the density of sand grains will go down and the stream will not narrow.

So the part about water molecules being attracted to each other is just saying that the bonds are strong enough to make it a liquid, not a gas.

[The Goober]

So after posting this, I looked at an actual smooth stream of water from my faucet and noticed something - at the very bottom of the stream, the stream stopped narowing, and instead it broke up and started mixing with air. Clearly, there is some point (before reaching terminal velocity) where the surface tension is not enough to keep the stream as a solid column of water and instead the density does go down as the water breaks into smaller droplets. So, the viscosity / surface tension does play a pretty big part here. I imagine that if one poured out a nice big stream of syrup from a very high distance, you would see the stream get pretty damn narrow before it starts to break up (and it may not break up at all if its still a stream when it reaches terminal velocity). I think this is the only reason that it would change things if you did this in a vacuum - without air, there is no terminal velocity and even the most viscous liquid stream would eventually break up into smaller droplets.