The force created by the earth's rotation, acting upon anything moving above the earth's surface by causing it to curve to the right (clockwise) in the Northern Hemisphere and to the left (counter-clockwise) in the Southern Hemisphere.
A gadget that can serve to demonstrate how easily this force can be counter-acted. It is called the Tornado Tube, and is manufactured by the DaMert Company (San Leandro, California), product number 2556, and received U.S. Patent 4625780.
It is a short red tube with internal threads at each end designed to mate with the common 2-liter soda pop bottles. After filling one bottle 2/3 full of water and screwing both this bottle and an empty one into the tube, you can watch how the water behaves while draining from the top bottle to the bottom through the constricted hole in the tube. Moving the end of the top bottle in a circular motion will induce a vortex (tornado) effect in that direction, without regard to the Coriolus force.
from The Remarkable Ocean World