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PURPOSE: To demonstrate a curve ball as an example of the Magnus effect.
DESCRIPTION: Throwing the ball with the appropriate spin will cause it to curve like a baseball pitch, or even to rise. The path of the ball will deviate in the direction the leading edge is rotating - that is, in the opposite direction of the shedding vortices. It will actually curve UP if you let it roll off the end of your fingers when you throw it.
SUGGESTIONS: Practice.
See Question of the Week #206 and Question of the Week #212 for information on using this demonstration to enhance class involvement.
Note: There is a certain amount of controversy regarding many of the demonstrations generally classified under the title of "Bernoulli effect." This phenomenon, among others, is due to the shedding of vortices as the ball rotates through the air, and is therefore a demonstration of the Magnus effect.
Click here for water channel photograph of curveball. The picture is a view from above the ball, with the ball spinning clockwise as it moves from right to left across your computer screen, shedding vortices toward the bottom of the photograph so as to curve toward the top of the photograph. (A right-handed pitcher would achieve this effect by throwing the pitch side-arm and letting the ball slip off the end of his fingers as he released it.) This photograph, taken from an article in a collection that is listed in the references for this demonstration, dealing with scientific issues in sports, can be found at the URL http://iweb.tms.org/ED/01-5085-185.pdf.
REFERENCES: Available.
EQUIPMENT: Styrofoam ball.
SETUP TIME: 10 minutes.
