Coriolis Effect

The Coriolis effect, sometimes called the Coriolis Force, is the factor which allows calculation of the apparent effects on moving bodies when viewed from a rotating Earth. Objects move, neglecting relativity effects, following Newton's laws. Newton's laws apply in an inertial or non-accelerated frame of reference. The Earth turns on its axis and we, standing on Earth, view and calculate the motions of the atmosphere from a rotating or accelerated frame of reference. The Coriolis effect or force is the conversion factor which allows us to do so. It is also the reason that Lows don't fill up and Highs don't just flatten out. For more on the concept, see the web page http://www.nws.noaa.gov/om/start.htm.

Demonstration of the Coriolis effect is relatively straightforward. It can be done in two dimensions using an old record player with a sheet of heavy black construction paper or flat black foam core cut to fit the turntable or a painted plywood turntable or in three dimensions by using a globe which has been painted flat black.

A turntable can be constructed in wood shop by making a 12" (or other size depending on your classroom) radius 5/8" plywood disk, a slightly larger square sheet of plywood as base. Drill holes in the center of the disk and the base. Connect the two by gluing a dowel in the base. A washer or two between the two will make it easier to rotate the disk around the dowel. Paint the disk flat black. Paint an outline of the continents with the North (or South) Pole at the center dowel rotation point. You may want to paint both sides as students who have lived in the other hemisphere are always curious to see how the Coriolis force works there.

When demonstrating with the NH side, locate New York City and San Francisco on the map and point out that sundown occurs later in California than it does in New York so the Earth turns counterclockwise as viewed from a point in space over the North Pole (the North Celestial Pole). Since Newton said things move in straight lines, ask a student to draw a straight line with chalk at a constant speed while the disk is turning. This is a little tricky and the student may need a ruler on some blocks to make it straight. When the disk is stopped, the line curves to its right.

If you are in the southern hemisphere and have used Capetown and Rio de Janeiro, you will be turning the disk clockwise as viewed from above the South Pole and the line will turn to its left.

The same thing will happen with the globe; however, the curvature will be more closely associated with the actual effect because the real winds blow over the rotating globe, the Earth. Practically speaking, with recent price reductions in globes, a 10 inch metal globe is inexpensive enough that it is a worthwhile investment.

Materials: Turntable or Globe painted flat black with map

Ruler and Chalk