GFDL - Geophysical Fluid Dynamics Laboratory

Effect of Rotation on Streams of Water
Turntables (lazy Susans) covered with dark paper
Large cylindrical containers
Thin dark tape to mark a diameter of the cylindrical containers
1 liter plastic bottles with the top portion cut off and a small hole a few cm from the bottom

1) Place the large cylindrical container on a turntable and place one of the 1 liter bottles in the center.  Fill the bottle with water and line up the exiting stream of water with the diameter line.  Viewed from above the water exits in a straight line.  Rotate the turntable both counterclockwise (like the Northern Hemisphere) and clockwise (like the Southern Hemisphere) and observe how the stream is deflected to the right and to the left respectively relative to the direction it is moving. 

Not rotating Rotating Rotating
Counterclockwise Clockwise
(Northern Hemisphere) (Southern Hemisphere)

Why does this happen?  If you think of the stream of water as stream of drops, each drop travels in a straight line once released, but each successive drop is launched in a different direction.  Linking the paths of the individual drops creates a curved stream.  This is schematically illustrated to the right for counterclockwise rotation like in the Northern Hemisphere.   Each dashed line represents the straight path of an individual drop.  The drops released earlier have traveled farther.  Later drops have traveled less distance in a direction rotated counterclockwise from previous drops.