The coriolis effect is one of the most misunderstood physical phenomena. The coriolis effect is cited as the reason behind the different ways that drains empty. Drains in the northern hemisphere are believed to swirl in one direction, and drains in the southern hemisphere the opposite direction because of the coriolis effect. In actuality, the direction in which a drain swirls has to do with the shape of the drain, and any motion in the water.
The coriolis effect is however a real phenomenon. First identified in 1778 by Pierre-Simon Laplace, and later described by Gustave-Gaspard Coriolis in 1835, the coriolis effect is a result of the daily rotation of the Earth. Each day, the Earth spins eastward on it's north-south axis. If you were to stand on the equator, in one day you will travel a distance equal to the Earth's circumference, which is a little over 40 thousand kilometers. In comparison, if you were to stand at a pole, your rotational trip would be negligible. An object that moves from the equator towards a pole will carry an initial eastward velocity that is greater than the eastward velocity of the surface of the Earth at the object's arrival. This means that the object will be deflected slightly from a straight path. This is the coriolis effect and it is too small to be detected at the scale of a kitchen sink.
It is detectable at larger scales, and is responsible for one of the most destructive forces of nature - the hurricane. Air masses that flow from the north in the northern hemisphere will gradually deflect to the west, and air flowing from the south will deflect to the east. As these air flows come together, a clockwise rotation in the air mass results. This air rotation sets the stage for a hurricane to form. In warmer months, warm ocean currents fuel the rotation by adding energy to the system, and destructive hurricanes are born.
