Is it physically possible to syphon a liquid from a pool of water back to itself? My thoughts: Variables involved are acceleration due to gravity, change in height, surface tension, air pressure, friction, radius inside and vacuums. If you take all the air out of the tube and place both ends below the surface of the liquid, the pressure at the ends, the radius, and the surface tension don't matter. Setting both ends at the same height means there's no acceleration. In this kind of system, it seems to me like all you would have to do is apply a force to get the liquid going, and it would keep flowing forever (disregarding friction) due to the vacuum created. idk, though. What do you think?