麦片圈效应 The Cheerios Effect

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The breakfast table's probably the last place you'd expect to find cool physics, but there is some awesome science happening right here, and you've probably seen lots of times without even realizing it. Ever notice how cereal tends to stick together in the middle of the bowl?

Or it clumps to the edges. That makes it easy to eat, but why does it happen?

We see this same clumpage with other objects too: paper clips, thumb tacks, even bubbles in a beverage will snap together. Maybe you've noticed this, but scientists didn't fully understand what was going on until 2005, when a pair of mathematicians decided to hit the lab, hit the kitchen, and hit the books.

What they found is cool. I'm super cereal.

Check this out. Breakfast cereal is less dense than water (and milk is mostly water) .

It's buoyant, it weighs less than the milk it displaces. That force of buoyancy pushes up on each ring, until it matches the downward force of gravity.

This interaction holds the Cheerios at the surface of the liquid, like little toasty rafts drifting together on top of a sea of cereal milk. It's a really complicated way of saying cereal floats.

But look closely at where the cereal meets the liquid. It's curved up.

The same thing happens at the edge of the container, thanks to the meniscus effect. Water molecules are stickythey're attracted to each other, but they're even more attracted to the edges of your bowl or glass, or to the edge of the cereal itself.

That "adhesion" forms a U-shape wherever the liquid meets an edge. A buoyant object will always be pushed up the liquid to the highest point on a meniscus.

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