Would a siphon work in a vacuum?

11 April 2010

Question

Would a siphon work in a vacuum?

Answer

The simple answer to that is, no, it wouldn't work. The general way that siphons work in general is that, essentially, you've got air pressure pushing down on both ends of your pipe. One end is higher than the other, then that can push - push it on both sides, push the water up to the top and then it carries and going. If there wasn't any air pressure, then you could form a bubble at the top of the tube and that bubble would expand and expand until the two levels of water are same level as that their two tanks. Okay, so that's the simple answer. The somewhat more complicated answer is that water has something called cohesion. The water molecules do stick together as related to the surface tension. And, therefore, as long as you don't form any bubbles, water can actually be pulled and actually will stay stuck together even at a negative pressure, even at zero pressure, or even as you can pull it apart, which is the reason why trees can actually go higher than about 30 meters which is the air pressure which will push the water up, or 10 meters, which push the water up. And so even with a very, very thin tube and until you get a bubble, it would work for a bit but not for very long.

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