# Secrets of the Perfect Water-Bottle Flip Unlocked: Thanks, Physicists!

Live Science | 9/25/2018 | Staff
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It was a craze that flooded the internet in 2016. People of all ages were flinging plastic bottles partly filled with water into the air, with a simple goal: tossing the bottle so it completed at least a single flip and landed upright.

This feat is much harder than it looks. But there's no need to flip out — bottle flipping just got a whole lot easier, thanks to a team of first-year physics students from the University of Twente in the Netherlands.

#### Water - Bottle - Liquid - Toss - Flip

The secret lies in the water in the partly filled bottle. As the liquid sloshes around during the toss and flip, the water redistributes the mass of the bottle, the students reported Sept. 19 in the American Journal of Physics. Just the right amount of water in the bottle (it varies, depending on the container's size) can bring a perfect flip within reach in every toss, according to the study.

To understand the physics behind this experiment, think of figure skaters spinning in place; when they pull in their arms close to their bodies, they rotate much faster. During a bottle flip, as the water spreads out inside the bottle (like figure skaters stretching out their arms), the opposite happens — the rotation slows down, study co-author Mees Flapper told Live Science in an email.

#### Physics - Conservation - Momentum - Flapper

"In physics, this is called conservation of angular momentum," Flapper said.

With the right amount of fluid to slow the bottle's spin, the container loses rotational...
(Excerpt) Read more at: Live Science
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