Monday, September 22, 2014

How Slippery is a Banana Peel?

This year's IgNobel in physics went to Kiyoshi Mabuchi and his colleagues for their study of whether banana peels really are as slippery as they are portrayed in cartoons:
To determine exactly how slippery a banana peel is, Mabuchi and colleagues sacrificed a total of 12 Cavendish bananas, the iconic yellow banana found on grocery shelves around the world. They placed the banana skins interior-side down on samples of linoleum (the scientists stepped on five different sections of each banana peel, for a total of 60 measurements). The linoleum was placed on a force transducer, a sensor that measures the force, weight and pressure applied to an object.

Then a volunteer stepped carefully onto the banana skin and pushed his foot forward. By measuring the horizontal and vertical forces, the scientists came up the coefficient of friction that results from a banana peel sliding along the floor.

It turns out that banana skins are, indeed, very slippery. The average coefficient of friction of a banana on linoleum was 0.066, and friction was only slightly higher for a banana on hardwood flooring (0.083), the researchers reported September 30, 2012, in Tribology Online. These frictional coefficients are very low, usually reserved for substances like Teflon (with a friction coefficient of 0.04), ice (around 0.05) or other well-lubricated surfaces. By comparison, rubber sliding on concrete has a frictional coefficient of 1.02.
I once stepped on a banana peel and my foot slipped right out from under me, nearly dropping me to the floor. My thought, of course, was "What to you know, it's true."

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