Why Does Coffee Spill When You Walk?
A $170,000 answer to a million dollar question
A somewhat obscure study, titled “Walking with coffee: why does it spill?” and published in the engineering journal Physical Review E in 2012, has resurfaced, in part because Senator Jeff Flake (R-AZ) recently called this coffee study out as an example of wasteful government spending. The research from the University of California, Santa Barbara looks at the reasons why coffee spills when you walk and was “partially supported by DARPA Young Faculty Award Grant,” according to the paper’s acknowledgements. Senator Flake’s office found that the authors got $170,000 from the U.S. government to figure out the answer to this seemingly simple yet common coffee conundrum.
It’s easy to mock the premise of the study, but if you’re being honest with yourself, you’ve probably asked yourself this very question. It’s the greatest question of the modern American workforce: How to navigate the minefield that is walking from the coffeemaker to your desk. At any moment, coffee could splatter and ruin your brand new, crisp white shirt (and somehow, you’re always wearing a new shirt when you spill coffee on it). If there’s a solution, I want to know and save myself from the embarrassment of walking around in my own slovenly, coffee-induced shame, and $170,000 of my hard-earned taxpayer dollars seems like an entirely reasonable price to pay if I never have to go to the dry cleaners again because I stupidly spilled coffee on myself. I want to be a coffee ninja, zipping back to my desk with a full mug and never spill a drop, and if this study will let me live that dream and avoid early morning destruction, I’m all ears.
Unfortunately, the answer is not as easy as becoming a ninja. Instead, it involves a lot of fluid dynamics.
Study authors Hans C. Mayer and Rouslan Krechetnikov explain that coffee spills are affected by the amount of liquid, the speed of walking, and the size of the cup. They asked volunteers to selflessly sacrifice their clothes in the name of science by walking in a straight line at different speeds holding a cup of hot coffee. The researchers then used photographic analysis to examine “the walking with coffee problem,” and they found that, “the motions of the human body, while seemingly regular, are quite complex and are coupled to a coffee cup and liquid therein, which makes it difficult to unravel the precise reasons behind coffee spilling.”
Mayer and Krechetnikov do offer some insights about how you can avoid spilling your coffee, like focusing on you mug and walking slowly. They even offer up a potential design for a new, spill-proof mug, which would come with “series of concentric rings (baffles) arranged around the inner wall of a container” to prevent too much oscillation, but they conclude, “despite the variety of spill control options, the simplicity and convenience of a common coffee cup will likely continue to outweigh the side effect of coffee drinking studied here—occasional spilling.”
Looks like science still has a long way to go to protect your white jeans from coffee stains.