Bottle Vortex
The bottle vortex can be constructed from two plastic lemonade bottles and a tube to connect them together at their necks. Such a tube can be home-made and fitted to the bottles be wrapping water-proof tape
many times around the necks. A better alternative is to try and obtain a plastic turnbuckle screw
from science toy stores, which will screw the bottles together more securely.
Before joining, one of the bottles is filled about three quarters full with water and a little food colouring is added to
make the demonstration more visual. When the bottles are joined, and turned so that all the water
is in the top bottle, no water should drain down to the bottom bottle since the change in pressure that this would cause in the upper and lower bottles produces a force that
balances the gravitational force pulling the water down in the first place.
However, when the bottles are given a rotational motion, to try and create a swirl in the liquid,
a vortex is formed and a miniature whirlpool will be produced in the upper bottle. At the
interface between the two bottles there is now a fast rotating stream of water which exchanges with
a whirl of air from the lower bottle, and fluid is exhanged between the two bottles, the water eventually all ending up in the lower bottle and the air forced up to the top bottle.