man's foot about to slip on banana peel

Pulp Friction

Tripping on a banana skin can have an audience rolling in the aisles. Assuming, of course, you’re careless enough to leave one lying around.

The now ubiquitous slipping-on-a-banana-peel gag is thought to date at least as far back as 1879, when Harper’s Weekly magazine warned its readers against following in the literal footsteps of inconsiderate fructivores. The great novelist Umberto Eco, for his part, believed that the iconic banana skin evolved as a visual euphemism for far deadlier heaps of dog detritus.

Never having slipped on a banana skin, I’ve often wondered just how dangerous they can be. And for that matter, whether it’s the inside or the outside of the fruit that poses the greater health hazard. Fortunately, these are exactly the sort of slippery questions that scientists have been falling over themselves for decades to peel back and really sink their teeth into.

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In 2012, Kiyoshi Mabuchi and colleagues at Japan’s Kitasato University in Japan decided to formally investigate this phenomenon, by studying the coefficient of friction of banana skins. Their results appeared in the journal of the Japanese Society of Tribologists, a term for scientists who study the way moving surfaces interact.

The coefficient of friction, often represented as µ, represents the ratio between the force of friction acting between two surfaces and the total force keeping them together. This can vary depending on whether the objects are moving or not, as well as on the surface used, so Mabuchi and his team experimented with stationary peels on both wood and linoleum flooring.

They quickly discovered that banana skin placed on linoleum with the soft side down had a frictional coefficient of 0.066, not far off that of an old ski sliding across artificial snow. Turning the banana peel upside down, however, roughly doubled the friction.

In order to help explain their results, the researchers used a microscope to examine the skins more closely. In doing so they found large quantities of a protein-rich gel stored in tiny capsules prone to bursting under pressure. Under the weight of say, a passing silent movie comedian, the liberated gel would run together to form a slippery substance known as a sol, in which tiny particles are suspended in a liquid medium. Blood is another good example of a sol – although for some reason its use never took off in the movies in quite the same way.

Mabuchi’s study eventually won the 2014 Ig Nobel Prize for Physics, good-humouredly awarded for research that makes you laugh and then makes you think. Much like you’d hope slipping on a banana skin would do.

Gilead Amit could trip on a carpeted floor while wearing crampon boots and holding a handrail. For the verbal equivalent, follow him on Twitter @gileadamit.

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