# My Siphon Challenge FINALLY

You can also think in terms of an airfoil, where the convex curve on top causes the air to flow faster over the top of the wing than it does under the bottom, thus lowering its density and decreasing its pressure, in turn creating a certain amount of suction on the upper surface of the wing and allowing gravity to cause the bottom surface to rest on the denser air beneath the lower surface of the wing.

The reverse is, of course, true concerning a spoiler on a racing car, which is an upside-down airplane wing intended to keep the car on the ground to inhibit its tendency to become airborne, the shape of the fuselage also being something of an airfoil.

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Drakkith
Staff Emeritus

Ok, but what does an airfoil have to do with a syphon? Or are you just elaborating on your statement in post 25?

Ok, but what does an airfoil have to do with a syphon? Or are you just elaborating on your statement in post 25?
The latter.

Ken G
Gold Member

"Suction"
This would need cohesion between the water molecules so the downhill ones could, like a chain, 'pull' on the uphill ones upwards. I have seen a movie which sort of implied that cohesion was, in fact, possible because a U tube more than 10m appeared to make a syphon with water.
Any opinions? Dynamic cohesion is a bit more acceptable, perhaps.????
The suction is just the difference in pressure between the atmospheric pressure at the top of the liquid, and the absence of atmospheric pressure in the evacuated tube. There's no need for any interparticle forces, an ideal gas would siphon just fine. Now, real liquids do have some contribution from interparticle forces, I'm just saying it's not an essential feature.

sophiecentaur
Gold Member

Of course we call the difference in pressures Suction. But that explanation doesn't apply to a syphon that operates above the '10m limit' - if indeed it does.

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I think a 10m+ siphon would work, just very slowly. The top of the tube would be full of water vapor instead of liquid.

Suppose the source body has a surface elevation of 10 meters, the tube goes up 20 meters and then down 30 meters to the destination body. Water travels up 10 meters from the source as liquid, then vaporizes. It then travels up another 10 meters and down 20 as vapor. It condenses 10 meters above the destination body. The weight of 10m of liquid + 20m of vapor > 10m liquid + 10m vapor so the siphon keeps going.

May be tricky to get started.

SAFETY WARNING: Isopropyl Alcohol is toxic and must not be swallowed, nor inhaled, nor allowed contact with the eyes. I only got a little in my mouth, and spat it out and rinsed my mouth immediately.

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I've just performed my experiment:

I used a store-bought 91% solution of isopropyl alcohol, a miniature (2 oz) martini glass as my donor tank, a miniature (2ox) gravy boat as my receptor tank, and a straw from a juice box for my hose (yes, I actually bought one just for this experiment).

Observations: having initiated flow via oral suction, flow continued as long as the mouth of the short end of the straw remained submerged beneath the surface of the liquid within the donor tank.

Measurements Taken: HEY, C'MON! I was working with tiny little glass vessels and a tiny little drinking straw that I could hardly hold in my hands. If want measurements, YOU take them!

Conclusions (keeping in mind my "Possible Sources of Error" discussion below):

1) Isopropyl alcohol is capable of being siphoned, thus suggesting that intermolecular hydrogen bonding is neither a significant nor a necessary force for the operation of a siphon system;

2) Isopropyl alcohol tastes terrible!

Possible Sources of Error:

!) The physical-chemical properties of ethyl alcohol and isopropyl alcohol may differ with regard to intermolecular attraction;

2) The 9% H2O content may have provided sufficient intermolecular hydrogen bonding to maintain the flow (although it wasn't a drip, but a good, strong flow).

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Now I'll spend the rest of my life looking in vain for a laboratory that will have me!

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