In 2016, the youth of America were obsessed with this one cool trick: the water-bottle challenge. The concept is simple, but it’s easier said than done. Just flip a full or half-empty plastic water bottle so it lands upright. Kids around the country chronicled their successes and failures on YouTube while the crinkling of tossed water bottles drove their parents crazy. The craze may have faded, but the physics still remains. That’s why, reports Mindy Weisberger at LiveScience, a group of young researchers recently published an article demonstrating how to land a water bottle every single time.
According to a press release, five first-year students at the University of Twente decided to unravel the physics of the water bottle challenge for a class on Dynamics & Relativity. Using a high-resolution camera, they filmed flip after flip of full and partially full water bottles as well as bottles containing two tennis balls. They then analyzed the videos and boiled the movements down to physical formulas. What they found is that a flip that causes the greatest decrease in angular velocity was most likely to stick the landing.
In practical terms, the team found that the best flipping bottle is one between 20 and 41 percent full. According to the study, landing a full bottle is almost impossible because the rotational speed of the bottle doesn’t change. With a partially full bottle, however, the water spreads out as it spins, changing the rotational speed.
“We didn’t look at the water in the bottle as fluid, but instead assumed it to behave as something rigid,” one of the student researchers Pim Dekker told Michaela Nesvarova at U Today earlier this year. In fact, the water bottles and tennis balls behaved the same way.
“Based on our experiments, we showed that the mass of a rotating object spreads throughout the object, reducing the velocity. That means that the distribution of mass makes the bottle slow down and increases the chances of a successful landing,” says Dekker.
The research appears in the American Journal of Physics, a pretty impressive publishing credit for undergrads. The team didn’t initially intend to wind up in a prestigious journal. “It started as a regular project for our Dynamics course,” Mees Flapper, one of the authors told Nesvarova. “We could choose any topic we liked and the water bottle flipping challenge was a big hit online at the time. As far as we know, there were no publications dedicated to the phenomenon. Our teachers Alvaro Marin and Jacco Snoeijer really liked the topic and later asked us to help them write a paper on it. That surprised us, but of course we agreed.”
The paper may be too late to save humanity from the constant crunch of flipping water bottles that made 2016 and 2017 a living nightmare for many, but Flapper tells Weisberger at LiveScience that the research has a bigger point.
“You shouldn't be afraid to think outside the box — even in an abstract, theoretical field [such] as physics,” he says.