"Thanks for thinking of me, especially on a thread about siphoning."
Posted on 05/11/2010 9:03:35 AM PDT by Gomez
Wow. I never realized how much people use syphons. I thought kids just used them to steal gas.
I nice trick I learned is to place two tubes into the tank to be siphoned and wrapping a cloth in a figure eight around the tubes. Below the cloth one tube should be long enough to reach as much liquid in the tank as needs siphoned while the other should be just long enough to enter the tank. Then push the rag into the tank opening trying to get the best seal that you can. Then blow into the “short” tube. I was amazed how well it worked.
LBFM ?
Nokes M. C. (1948), “Vacuum siphons”, Am. J. Phys. 16: 254
Simple: reduce the atmospheric pressure around the shorter leg and see if any flow occurs. No mistake has been found, just someone trying for a “gotcha”. Ho Hum.
Who gives a crap and who uses a syphon?
Just using increase in pressure to get the flow going, then gravity does the rest, so long as you equalize the pressure inside and out of the tank, not allowing the pressure to become greater outside than in. Thanks for the word picture. Well presented
The Australian Physics Professor is wrong.
The only reason water flows UP the pipe is because atmospheric pressure PUSHES it up.
If there was no atmospheric pressure, nothing would happen.
Of course, atmospheric pressure is caused by gravity, and gravity is what pulls the water down on the other side.
But if you had a vacuum on both sides, the water would run down both sides of the pipe, because the “suction” created by the water on the longer side of the pipe wouldn’t overcome the “suction” of the vacuum.
And a siphon wouldn’t NEED gravity, although by definition I guess it does; you could siphon with a pump, or any other mechanism that caused a lowered atmospheric pressure.
I guess in the end, you could argue that “siphoning” is the special case of suction where the suction is created by gravity pulling down on the fluid.
Oops, sorry, wrong article!
Think about it; the receiving end is lower, so it is under greater ambient pressure than the higher, sending end.
Assuming that both the ambient pressure and experienced gravity are nonzero, the gradient in ambient pressure works to impede the flow, but only very slightly compared to the flow-creating differential due to the weight difference in the two halves of the siphon.
The difference in the magnitude of the two effects is proportional to (1) the strength of the gravity, and (2) the difference in mass density between the ambient air (or other gas) and the liquid, and (3) the net length of the drop.
The siphon would still break. It is the release of the water itself into gaseous form that will form the gap.
This is like a barometer. I used to wonder, “how can a space open up at the closed top of a column of mercury, so that the column will reach about 760 mm and no higher?” The answer, of course, is that the space is a near vacuum, with a small amount of mercury vapor.
No. The energy is provided by gravity. The pressure is the difference in height of the 2 surfaces. The amounts of water in the 2 reseviors and their shapes do not matter, only the head does. The head is the driving pressure.
p = mgΔh, where Δh = the difference in height of the 2 surfaces. g is the acceleration of gravity and m is the mass/unit area.
The mass/unit_area of air is too small to have a significant effect on the system. Air is essentially equivalent to a vacuum in this system. The cohesive energy density of the liquid is what keeps the water together.
"Thanks for thinking of me, especially on a thread about siphoning."
Siphons also work in zero gravity, because of inertial. Once started, they will continue until the frictional losses diminish the momentum to zero.
What a brilliant way to agree with my position!
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