Does water go down the drain counterclockwise in the northern hemisphere and clockwise in the southern hemisphere?

    It all depends upon how the water was introduced and the geometric structure of the drain.

One can find both counterclockwise and clockwise flowing drains in both hemispheres. Some people would like you to believe that the Coriolis force affects the flow of water down the drain in sinks, bathtubs, or toilet bowls. Don’t believe them! The Coriolis force is simply too weak to affect such small bodies of water.

In his work “Sur les equations du movements relative des systems des corps” (1835) the French engineer Gaspard Gustav de Coriolis (1792-1843) first described this force. The Coriolis force is caused by the earth’s rotation. It responsible for air being pulled to the right (counterclockwise) in the Northern Hemisphere and to the left (clockwise) in the Southern Hemisphere.

The Coriolis Effect is the observed curved path of moving objects relative to the surface of the Earth. Hurricanes are good examples. They curve to the right in the northern hemisphere and to the left in the southern hemisphere. What makes the hurricanes move in this way is the Coriolis force.

What happens at the equator? The Coriolis force is too weak to operate on the moving air at the equator. This means that weather phenomena such as hurricanes are not observed at the equator, although they have been observed at 5 degrees above the equator. In fact, the Coriolis force pulls hurricanes away from the equator.

For a more detailed explanation of the Coriolis Force see Science World, http://scienceworld.wolfram.com/physics/CoriolisForce.html

Related Web Sites

"Getting around the Coriolis effect" - This paper provides a scientific explanation of the Coriolis effect complete with diagrams and examples. It was written by David J. Van Domelen, of the Ohio State University Department of Physics, Physics Education Research Group. Danish Wind Industry Association - The Coriolis Force This Web site provides animated models of how the Coriolis Force works. Bad Coriolis - The author of this Web site sets the record straight about the Coriolis Force. Presented are numerous cases where incorrect information was provided by reliable sources. Also included are Frequently Asked Questions. Coriolis Force - Included in this Web site, from the University of Illinois at Urbana-Champaign, is an explanation of the Coriolis Force and a video demonstrating the Force.

Further Reading

Salzsieder, John C. Exposing the bathtub Coriolis myth. The Physics Teacher, V. 32, Feb. 1994, v32: p107. Stommel, Henry M. and Dennis W. Moore. An introduction to the Coriolis Forces. New York, Columbia University Press, c.1989. 297 p. World of Physics. Detroit, Gale Group, 2001: 135-136.

For more print resources...
Search on "Coriolis," "hurricanes," and general books on meteorology and physics in the Library of Congress Online Catalog.

Hangs on to tree during hurricane. From the Prints and Photographs Division of the Library of Congress.

Super Typhoon Imbudo - China on July 23, 2003 From NASA 's Earth Observatory at
http://earthobservatory.nasa.gov/NaturalHazard/
natural_hazards_v2.php3?img_id=10821

From Environmental Health Perspectives
Volume 111, Number 5, May 2003
http://ehpnet1.niehs.nih.gov/docs/2003/111-5/ss.html

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