Siphon Model
Thursday, May 3, 2012 at 11:07PM
Kossover, Zeke in Demos, conservation of energy, siphon

A siphon is usually presented a tube that has one end higher than the other and is completely filled with liquid. A Google image search gives dozens of pictures along that line. 

The explanation that often goes with these pictures has to do with atmospheric pressure. That air pressure is slightly higher on the high side (A) and slightly lower on the down side (B). That's true but not the whole story. The difference in air pressure helps to hold the water together and does push it, but a siphon will work without air pressure. 

A better way to think of a siphon is probably good ol' conservation of energy. Though it takes energy to lift the water over the lip (from A to C) of the first side, the energy can be gained can be returned if the water on the other side ends up lower than where it started in the first side. 

The hard part is actually getting the energy back to the first side to lift the next bit of water. Atmospheric pressure helps to hold the water together so it doesn't break into two pieces at the bend. 

If the material can hold together on its own, then the siphon could work in a vacuum. The beaded chain in my video demonstrates this idea. If you pull it over the top and let it hang to the table it. 

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