When, say emptying a fish tank, if you put a tube in the water and have the other end outside the tank but lower than the water level, you can suck it, and the water will keep flowing until the tank empties.... What forces enable this to happen?
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- AJ -
ANSWERS: 2
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hydrostatic pressure
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You've described a siphon. Gravity is the ultimate force that drives the system -- the water is seeking a lower point. However it requires air pressure to push the water up the tube before it can go down. If you tried to empty your fish tank in this manner on the moon, where there is no atmosphere, water flowing down and out the lower end of the tube would not be able to "suck" additional water up from the tank, because there would be no air pressure to push on the water. Siphons require gravity and air pressure.
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