Unexpected Peeling


By Tanya Silverman

Photo courtesy of Quinn Dombrowski.

So many slapstick actors and cartoon characters have toppled on the ground due to slipping on unexpected banana peels.

Because the situation is such a comedic cliche on the screen, Japanese researcher Kiyoshi Mabuchi expected there to be some scientific study completed on the slipperiness of a banana peel against the ground somewhere in history.

There wasn’t.

Therefore, Mabuchi and his colleagues took it upon themselves to officially run such an experiment. The research team measured the frictional coefficient–the ratio of the force between an object against a surface along with the frictional force resisting the object’s motion–under a banana skin when it rubs against the floor.

They set a “force transducer with six degrees of freedom” on a linoleum surface to simultaneously measure “both frictional force and vertical force” as a shoe sole rubbed against a banana peel.

On average, the situation’s frictional coefficient was determined to be about 0.07–a figure proving that when a human foot rubs a banana peel that rubs against the floor, it is indeed slippery. The fruit-floor lubrication, they wrote, was largely due to the viscous polysaccharide follicular gel that a banana skin exhibits. When a foot tramples upon the fruit’s epicarp, the impact causes the gel to be released onto the surface below, leading to extra slickness.

Completed in 2012, the study, titled “Frictional Coefficient under Banana Skin”, was published by the Japanese Society of Tribologists. (Tribology is the science of surfaces rubbing.)

Last month, Mabuchi’s study came to the world’s attention when it won an Ig Nobel 2014 award in the physics category. Ig Nobel Prizes are meant to award unusual achievements in science. Other prizes at the 24th annual ceremony were given to those studying the face of Jesus in toast, determining how pork can cure uncontrollable nosebleeds, and testing how reindeer react to humans who dress up as polar bears.

BTR took some time to catch up with Mabuchi on the logistics of the study as well as his background, and in dong so, found out some unexpected facts about the world of banana lubrication.

Mabuchi is pleased that he won the Ig Nobel award and the public’s positive reception. In his career, he specializes in studying biotribology, a scientific field that focuses on the friction and lubrication exhibited by organic systems–often between joints.

Mabuchi, who’s currently chairman for the Japanese Society for Biotribology, explains that banana peel lubrication came to his attention through examining the biomechanics in musculoskeletal systems. For over 30 years, Mabuchi conceptualized the similarities between the low friction mechanism exhibited by synovial cartilage and banana peels on floors.

As such, if you watch the video of Mabuchi winning the physics prize at the Ig Nobel ceremony, you can witness him accepting the prize by singing a slow song while he’s holding a banana and motioning the elbow of a model skeleton arm to the cheery audience.

The winning study’s text states that the “lubricating ability of the banana skin can be proved to be excellent.” When inquired whether the ability could be put to any practical use, Mabuchi cites a significant date in banana lube history: Jan 23, 1941. In Beaumont, Texas, 3.5 tons of “well-ripened bananas” were wiped on the sides of the Cape Lookout cargo ship to launch into the water. People actually used bananas to slide ships into water at this time because buying the fruit was cheaper than grease.

When Mabuchi’s team was measuring the friction coefficient of banana skin against the floor, they also measured that of tangerines, apples, and citrons. All other specimens exhibited more friction–thereby, were less slippery–than the skin of a banana, largely due to the polysaccharide gel.

BTR asks Mabuchi whether we should be wary of other stray fruit skins that his team did not include in their research. He responds that the sweeter fruits that contain this viscous gel in their peels, like peaches or melons, might also exhibit low friction when discarded on the ground.

But don’t get too scared; Mabuchi reasons that a peach’s outer layer is too thin, plus the “peel of a melon is too rare to be put off on floors.”

When asked if banana peels on floors are actually dangerous to us pedestrians, Mabuchi responds positively, citing a written ordinance: Cambridge Municipal Code, 12.16.100 Sidewalks–Obstruction–Fruit Peelings. The local Massachusetts code states: “No person shall throw or place upon any sidewalk or crosswalk any banana skin, orange peel or other slippery substance.”

Laws and ship lube and biotribology aside, is Mabuchi a fan of slip-and-fall slapstick comedy? Well, not particularly.

“In fact, I dislike [when people laugh at the] sacrifice of someone, for example, who falls by banana peels,” he responds. “I think that humor must be based on humanism.”

Can aspects of moralistic or intellectual comedy be taken under such scientific examination, though? Perhaps we’ll have to wait until the Ig Nobel 2015 awards to find out what strange studies surface.