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Physicists measured forces behind why Cheerios clump together in your bowl, Ars Technica

Physicists measured forces behind why Cheerios clump together in your bowl, Ars Technica


    

      Have a little physics with your breakfast cereal –

             

It all comes down to gravity, surface tension — and tilt.

      

      

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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 ofFroot Loopsa new paperin 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

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. Apaperin the American Journal of Physics outlined the underlying physics, identifying the culprit as a combination of buoyancy, surface tension, and the so-called meniscus

It all adds up to a type ofcapillary 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.

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Harris Lab / Brown Universityentirely wrongthe droplets’ behavior to how galaxies and black holes interact by deforming space around them. Making the surfaces softer or harder or changing the layer’s thickness essentially “tunes” the system so the droplets can be easily manipulated.

Measuring the actual forces at play on a small scale proved daunting. Typically, this is done by placing sensors on objects and setting them afloat in a container, using the sensors to deflect the natural motion. But Cheerios are small enough that this was not a feasible approach. So the Brown researchers used two 3D-printed plastic disks, roughly the size of a Cheerio, and placed a small magnet in one of them. Then they set the disks afloat in a small tub of water, surrounded by electric coils, and let them drift together. The coils in turn produced magnetic fields, pulling the magnetized disk away from its non-magnetized partner.

“The magnetic field gave us a non-mechanical way of applying forces to these bodies,” said co-author Daniel Harris

Finally, the scientists measured the intensity of the magnetic field. As Sophie Chen wrote

at Physics:

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