PURPOSE: To illustrate vorticity in a perhaps tricky way.
DESCRIPTION: Q: What is the quickest way to get the water from one bottle into the other? A: Turn it upside down and give it a couple of quick rotations. This starts a circular rotation of the water, so that as it falls down into the lower bottle it stays on the outside of the neck, allowing air to rise up into the upper bottle simultaneously. Simply turning the bottles upside down will trap a small amount of air in the upper bottle and not allow more air to rise, quickly causing the water flow to cease. Tilting the bottle allows air to fill the upper bottle while water is flowing, but is not as fast as using the vortex technique.
SUGGESTIONS: Before doing the experiment let your students try to figure it out.
REFERENCES: (PIRA 250.30)
EQUIPMENT: Two coupled two-liter bottles with water filling one.
SETUP TIME: None.
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