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Find out why stacked apples seem so stable, but removing the “wrong” apple can lead to a produce-aisle disaster
Presented Monday, March 15, 2010
Robert P. Berhinger
Theorists have always believed that friction plays a great role in avalanche-like collapse of a granular piles, but the predictions have proven difficult to test experimentally. We devised an experimentally controlled way to demonstrate the impact of friction, accessible to all who dare try.[1-3] With the aid of a middle school assistant, we studied and filmed piles of apples, oranges, and onions as one or more pieces of fruit were removed. Among other things, we discovered that increasing the friction of the onions (by peeling them) vastly decreased the likelihood of collapse. Our work includes videos written by, produced, and starring our 7th grade assistant, some of which are posted on the Physics Today YouTube channel.
Photoelastic ellipses simulate a two-dimensional fruit pile. When viewed through polarizers, the ellipses manifest force chains (white) that reveal weight-supporting particles. Removal of a weight bearing particle risks entire pile collapse.
 J. Krim and R.P. Behringer, Physics Today, (September, 2009) volume 62, page 66. Online article is free to the public.
Reporters may freely use this image as long as they include the following credit: "Image courtesy of J. Krim and R.P.Berhinger, Duke University and Physics Today".
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