Physicists Measured Forces Behind Why Cheerios Clump Together in Your Bowl
upstart writes in with an IRC submission for Runaway1956:
Physicists measured forces behind why Cheerios clump together in your bowl:
Those who love their Cheerios for breakfast are well acquainted with how those last few tasty little "O"s tend to clump together in the bowl: either drifting to the center, or to the outer edges. It's been dubbed the "Cheerios effect," although I can state with confidence the phenomenon can also observed in a bowl of Froot Loops. Now a team of physicists has made the first direct measurements of the various forces at work in the phenomenon, described in a new paper in Physical Review Letters.
"There have been a lot of models describing this Cheerios effect, but it's all been theoretical," said co-author Ian Ho, an undergraduate at Brown University. "Despite the fact that this is something we see every day and it's important for things like self-assembly [for micro robotics], no one had done any experimental measurements at this scale to validate these models. That's what we were able to do here."
The Cheerios effect is found elsewhere in nature, such as grains of pollen (or, alternatively, mosquito eggs) floating on top of a pond, or small coins floating in a bowl of water. A 2005 paper in the American Journal of Physics outlined the underlying physics, identifying the culprit as a combination of buoyancy, surface tension, and the so-called "meniscus effect."
It all adds up to a type of capillary action. Basically, the mass of the Cheerios is insufficient to break the milk's surface tension. But it's enough to put a tiny dent in the surface of the milk in the bowl, such that if two Cheerios are sufficiently close, they will naturally drift towards each other. The "dents" merge and the "O"s clump together. Add another Cheerio into the mix, and it, too, will follow the curvature in the milk to drift towards its fellow "O"s.
DOI: Physical Review Letters, 2019. 10.1103/PhysRevLett.123.254502 (About DOIs).
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