|MadSci Network: Physics|
Siphons work on the principle of using air pressure, so in a vacuum, a siphon will not work. The questioner is muddying the waters by stating the tall narrow cylinder has less air pressure than the large wider container. Pressure is defined as force per unit area, so a wider area has the same amount of pressure as a smaller one, by definition. If water is in two containers, one of which is "lower" than the other, then a tube running from the higher container to the lower container will allow water to flow as long as the water level of one is higher than the water level of the other, and the tube is below the water level. This is gravity in action, and is a different case from a siphon. Since I haven't looked at the diagram I may be missing part of the details, But, simply put, a siphon will not work in a vacuum, since there is no air pressure. For further ideas about water pressure and vacuums, read the chapter in Richard Feynman's book, "Surely you're joking, Mr. Feynman," where he describes his experiment with a lawn sprinkler, a large carboy, and a vacuum pump.
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