# does water flow through a funnel faster clockwise or counterclockwise?

Discussion in 'General Science & Technology' started by sculptor, Feb 18, 2018.

1. ### sculptorValued Senior Member

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Does water flow through a funnel faster clockwise or counterclockwise?

That's it.

Also, would this be different in northern or southern hemisphere?

3. ### RainbowSingularityValued Senior Member

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1,637
no
it maintains its relationship with Gravity, Surface tension, electrical charge & the earth rotation dependant on where in the world it is.
(does that cover it all?)
obviousely dependant on the height, volume & shape of the funnel this would also effect it.. and right down to the type of funnel based on its ability to stick to, or repel water(and any electrical charge the funnel may have)

5. ### sculptorValued Senior Member

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OK
Clarification:
When pouring water from one container to another through a funnel:
Surmising that water normally flows out of a drain clockwise here in Iowa so "going with the flow" by pouring the water into the funnel so that it starts clockwise would logically seem to allow it to flow faster

the question obtains
even if that is true, would it be only initially?
or would that extra boost of speed last throughout the complete pour?
(assuming that I could keep a constant height of water in the funnel)

7. ### Janus58Valued Senior Member

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The idea that water flows clockwise through a drain in the Northern hemisphere in and counter-clockwise in the Southern is a myth. On that scale, the Coriolis effect is just too small to have any measurable effect. Irregularities in the shape of the drain etc. has a much larger effect.

That being said, Consider the typical cone shaped funnel. What happens if the fluid in it is rotating fast? it tends to move outward and thus up the sides of the funnel. This acts contrary to gravity pulling down through the throat of the funnel. Thus the greater the angular momentum of the water flowing in the funnel, the slower it would flow out. (if the water were rotating fast enough you could keep it from passing through the throat at all.)

If you want the water to flow the fastest, you want it to have no rotation what so ever.

8. ### DaveC426913Valued Senior Member

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It does not. This is a myth.

Coriolis Force does not impact the rotation of flow in anything but the largest of structures. (Note, not just size but density. Water is 784 times more dense than atmosphere)

Consider: pick up your sink. Hold it real steady. Now start turning it at a rate of 1.5 degrees (one-and-a-half inches) every hour. That's 64 micrometres (1/16th of a millimetre) per minute.

How much rotational motion do you think you're imparting?

9. ### YazataValued Senior Member

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I agree with Janus and Dave. Coriolis 'force' is apparently an important factor in the formation of storms in the Northern and Southern hemispheres, so cyclonic storms in the US and Australia supposedly do rotate in opposite directions. (I've never verified that.) But toilets and funnels are too small for the coriolis effect to be a major factor. A much bigger factor would be how you are pouring the water into the funnel. How fast? Left hand or right hand? Directly down the center hole or off center?

The question is usually asked about toilets. I believe that when you flush a toilet there's a built in water jet that would determine the direction of rotation.

(I put coriolis 'force' in quotes because it's a 'fictitious force', isn't it, like centrifugal 'force'? My layman's understanding is that it derives from conservation of angular momentum as radius of rotation changes.)

Last edited: Feb 18, 2018
10. ### BowserRight Here, Right NowValued Senior Member

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I was told the same about water rotation while in school.

11. ### iceauraValued Senior Member

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Although the theoretical objections above, which presume some idealization and simplification of circumstance, are sound, in practice some kind of a swirl sometimes seems to speed things up. In particular, if it thins the flow enough to keep a hollow in it the flow stays laminar at higher speeds - at least, that's what it looks like.
My take: by lengthening the total path and thinning the stream the swirl allows a higher rate of steady or net volume flow. That's a guess. Anecdote.
(Doesn't work for high viscosity, or funnels either very narrow and long or very broad and short. Works for filling bottles with water when the funnel seals the mouth)

The best direction of the swirl seems contingent - whether left or right handed pouring, say.

12. ### Q-reeusValued Senior Member

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Agree with those saying rotation direction is in practice irrelevant. But as to what empties a bottle faster - YouTube to the rescue:

And many more just like it.

13. ### RainbowSingularityValued Senior Member

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1 container
1 funnel
1 other container

= 3 items not counting the water and not counting the person pouring it.

Because of the nature of waters physics properties, the height-distance you pour the water from is going to make the innitial biggest difference.
(can water store inertial energy & maintain it at 0 atmosphere with no additional electrical charge and no additional presure using only its own terminal fall gravitational force?) ?

it is a good question as the innitial un-educated observation of the event appears to illicit physics principals which are indeed not rules of laws.

14. ### exchemistValued Senior Member

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Aha, but that is, he says in the video, because with the bottle there is an advantage in allowing air to enter as the water leaves. So that would not apply to the general case of water going down a plughole. So there is no conflict with what Janus said earlier.

15. ### DaveC426913Valued Senior Member

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Both of these actions: lengthening the path and narrowing the stream, each reduce the rate of water exiting.

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16. ### Q-reeusValued Senior Member

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Well there are small plugholes, and then again there are big, multi-hole plugholes. So it would depend on the specifics. But if you check back, the argument got to be over emptying via a funnel. I've no doubt one could make it empty slower than the the straight-down gurgle-gurgle method, by creating excessive vortex speed. The trick to optimum emptying rate would be getting enough swirl motion to create that central evacuated vortex, without too much centrifugal force fighting against gravity.
Anyone planning on doing the optimization calcs via hydrodynamics maths? Didn't think so.

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17. ### Write4UValued Senior Member

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This may be of interest:
https://www.straightdope.com/column...-counterclockwise-in-the-northern-hemisphere/

18. ### Q-reeusValued Senior Member

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Yeah I think we are all on board now re clockwise vs counterclockwise on bathtub scale situations. How you pull the plug out will be the main determinant, not piddling Coriolis effect, all other things being equal (shape of basin, position of plughole etc.). But my last post was regarding the case of deliberately creating swirling motion - as in that YouTube vid. Clock 'speed' not direction is what matters there.

19. ### iceauraValued Senior Member

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Not if they enable a more than compensating increase in average velocity via laminar flow - which appears to be the case, in certain common situations.
There is always displacement of air to consider - even from an open source. Also, there is turbulence created within the stream - not just by returning air - to consider.

Again - just anecdotal here. I swirl stuff a bit - just a little - when pouring splashy liquid through a funnel - seems to work. Cuts down on the splash, too - a related phenomenon, is my guess.

Last edited: Feb 20, 2018
20. ### exchemistValued Senior Member

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Didn't we once have a thread in which we examined the truth of the claim that a railway track running North-South would get greater wear on the inner side of the western rail, because of the Coriolis effect? I seem to recall a sideways thrust equivalent to several tens of kg weight, for a fast-ish locomotive. But maybe that was on a different forum......

21. ### Q-reeusValued Senior Member

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Yes I recall it too, and iirc it was a 'confirmed'. Too lazy to check the sums, but I'll blind wager the true figure will be hugely swamped by such other factors as prevailing cross winds, bias in lateral inclines & radius of bends along the journey.
And of course a Tropics Express run has little if any concern re Coriolis, compared to it's Polar Express counterpart!
(edit note: I had it backwards first up!)

Last edited: Feb 20, 2018
22. ### Janus58Valued Senior Member

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The force would be dependent on the latitude of the train. The tangential velocity for any point on the surface of a sphere is w cos(x)r where w is the angular velocity, x the angle from the equator, and r the radius of the sphere.
If we use an example where both r and w = 1 we can easily compare the change in tangential velocity for moving from the pole to one degree from the pole and moving from the equator to 1 degree from the equator.
Moving 1 degree from the pole gives a difference of cos(89)-0 = 0.01745
Moving 1 degree from the equator gives a difference 0f 1- cos(1) = 0.0001523, a much smaller difference.
Thus the sideways acceleration felt by the train as it moves North-South is weakest near the equator and strongest at near the poles.

23. ### exchemistValued Senior Member

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Indeed, it must logically be zero at the equator as it reverses direction as you move into the opposite hemisphere. I think I assumed a latitude of 45 degrees for the exercise for convenience.