BACKGROUND:

The rotation of the Earth affects the outer portions of the Earth.  The effect on the oceans is a steady and continuous reaction, which causes the general direction of the ocean's motion.  This is called the Coriolis Motion, whereby water is deflected to the right in the Northern Hemisphere and deflected to the left in the Southern Hemisphere, as shown on the diagram above.  

The Coriolis Motion is named after the French mathematician,  Gustave Gaspard Coriolis (1792-1843). The Coriolis Motion is a visible effect of the Coriolis Force caused by a rotating sphere. In the Northern hemisphere the wind tends to rotate counterclockwise (as seen from above) as it approaches a low pressure area. In the Southern  hemisphere the wind rotates clockwise around pressure areas.  

It is also referred to as the Coriolis Effect, which refers to the changing motion dependent from where you look.  An example that you can use to illustrate this is that when a ball is thrown to someone from a merry-go-round the ball moves in a straight line but because the merry go round is moving, the ball appears to travel in a curved path if you are looking above.   

The Coriolis Motion is a difficult phenomena to fully understand, but it is important for children to realize the influence of a rotating sphere on the motion in the ocean. 

PROCEDURE:

1. It is a wise old tale that states that toilets flush to the right in the northern hemisphere and to the left in the southern hemisphere.  Theoretically  there should be some influence on the water, but  the shape of the bowl and where the water emerges influences the movement more.  This tale should be easy to test. Before you start your discussion on the movement of the oceans, have students go home and look at what direction their toilet bowls flush. If there is more than one bathroom, have them record whether the bowl is facing east, south, west, or north. Remind students not to waste water.
     
2. Have students record the results as a homework assignment and then tabulate the results on the board in the following manner:

3. Discuss the results of the class.  It will probably be a collection of insignificant data, but it is the idea of asking the students to test a statement.  Discuss that theoretically, the motion of the Earth should make the bowls in the north go left to right and in the southern hemisphere the bowls would flush right to left .  On the equator, theoretically the bowls will flush 50% one way and 50% the other way. However, the force caused by the rotating sphere is so small in a toilet bowl, students will probably not see the effect.  But it is a way for students to start thinking about the Earth rotating  and its effect on the oceans.  

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