Eli5, how does siphoning liquid from a low point over a high point and then to a low point again work.
In: 1
the liquid from the low point to the high point weights less the the liquid from the high point to the lower point
so the liquid on the light side gets “pulled*” by the liquid on the heavy
side
really pushed by air pressure, but hey ..
Think of the hose you would be using as a closed system. When you suck on one end the only way to equalize the suction is to draw some liquid from your source into the hose.
Now if the hose is full and you unblock one side the liquid will be held in the tube (like a drinking straw if you put a finger over one end) if you open both sides as the liquid falls out it will “pull” in air to replace the liquid. This pulling of air creates a vacuum and if you put the end of the hose in a liquid it would use that same vacuum to pull liquid into the tube.
So now we have a closed system that is “pulling” liquid into it and is letting gravity “push” the liquid down. You only need to provide the suction at the start because once the liquid is flowing the closed system can not equalize until you lose the vacuum in the tube or gravity runs out. Does that make sense?
Think of the smallest pieces of the water (the water molecules) as being on a tug-of-war team except there’s no rope–they’re all just grabbing onto one another. In the middle of a closed tube, it takes an impressive amount of force to actually pull them apart from one another since there’s no other material (such as air) around as there would effectively be nothing to fill the gap left in-between (we’d call the resulting nothingness, in this case, a “partial vacuum”) When you have water in a tube acting as a siphon, one side is always longer than the other. Both sides consist of the water molecules being pulled *down* by gravity, but the longer/heavier side will be able to pull *up* its “opposing team”.
The above is a slight oversimplification in some ways because it neglects to note that those partial vacuums are difficult to create on Earth mostly due to the squeezing force of the weight of the atmosphere (air pressure) which is what’s causing the water molecules to be squeezed tightly to one another in the first place. You can’t generally siphon water over a height of about 33′ on Earth’s surface because the force of that many molecules’ collective weight pulling down will “tear” the water and leave a gap of nothingness. This same “tear” of a column of liquid in a tube happens at about 0.76 meters (2.5′) for mercury (the pieces of which are much heavier), and such a tube with one side of a “torn” liquid is called a barometer, and that’s why air pressure’s strength is measured in mmHg (“millimeters of mercury”). The column can rise higher against the nothingness when the air squeezes it more.
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