What happens if you walk backward while carrying a cup of coffee?

One would assume that walking backward with coffee, especially when it’s piping hot, would be nearly as dangerous as running with scissors. Not so, according to the 2017 Ig Nobel Prize winning study for Fluid Dynamics. According to Korean physicist Jiwon Han, you will likely spill less walking backward than forward. However, your chances of tripping, or crashing into a colleague (also walking backward with coffee, ha ha) “drastically increase”.*

“Rarely do we manage to carry coffee around without spilling it once. In fact, due to the very commonness of the phenomenon, we tend to dismiss questioning it beyond simply exclaiming: ‘Jenkins! You have too much coffee in your cup!’”

– Jiwon Han

As reported in this “SmartNews” post by Smithsonian Magazine, Han advises a claw-like grip on top of your cup, rather than using the handle. Other tips from University of California researchers, reported here by LiveScience, are to gradually accelerate to a very slow walk, thus avoiding disruptive oscillations, and keep your eyes on the cup, not the ground.

My secret to stop spillage is to use a very large cup and fill it only two-thirds of the way, e.g., 12 ounces of hot coffee in a 16-ounce Styrofoam cup.  The ultimate solution is to use a spill-proof, lidded container. However, I prefer drinking from a cup, if possible.

*(Source: Chemical and Engineering News, 9/18/17, Newscripts—“Curating quirky science since 1943.”)

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