In the first place, we perforated a hole of 1 cm in the corks of the two bottles. Soon we filled one of the bottles with water until approximately three fourth parts and if united the two bottles by the corks. In order to unite the two bottles insulating tape can be used. Is very important a good union between the bottle.
When the bottle with water is on the empty bottle it is observed that the water does not fall easily to the inferior bottle, but if we give a circular movement to the superior bottle is generated an eddy and the water falls easily.
When placing the bottle in the superior part, water does not fall by the little compressibility of the air locked up in the inferior bottle that does not leave space to the water that falls. When the eddy is generated when moving the superior bottle, it is put in communication the air that is in both bottles and the water of the superior bottle falls easily in to the inferior bottle.
Colegio Sagrado Corazón (Esclavas)