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PURPOSE: To illustrate properties of fluid flow in a counterintuitive way.
DESCRIPTION: Place the cardboard piece at the end of the spool with the pin sticking up through the hole of the spool. Blowing into the other end of the spool keeps the cardboard in place. The pin keeps the cardboard from sliding away. It will not blow off! Cessation of blowing allows the cardboard to fall off.
SUGGESTIONS: You can probably win a few bucks with this one at the local pub.
REFERENCES: Available. (PIRA 2C20.41)
This demonstration is often incorrectly referred to as "Bernoulli Lift," or "Bernoulli Levitation." A paper in the American Journal of Physics (Waltham, et. al.) listed in our reference file describes a larger version of this demonstration, but does not use the Bernoulli effect in explaining why it works. The version of the paper submitted to AJP is found on the author's web site: http://www.physics.ubc.ca/%7Ewaltham/air/b_demo.pdf, showing that the author used quotation marks in naming the demonstration "Bernoulli" Levitation. He did not really believe or propose that the demonstration involves the Bernoulli effect, but, rather, called the demonstration by a familiar name from which it could be identified by most physicists and physics teachers. (Click here for a copy transferred to our web site.)
Click here to view the first page of the paper as it appeared in the AJP.
EQUIPMENT: Cardboard with thumb tack, spool.
SETUP TIME: 10 minutes.
