Scientists Share Secret To ‘Cereal Clumps’

The morning enigma of why cereal clings to the sides of a bowl of milk has finally been explained in a manner comprehensible to the average student.

According to Harvard Applied Mathematics Professor Lakshminarayanan Mahadevan and Cambridge University graduate student Dominic Vella, it’s just a matter of basic physics.

“Many scientists have researched and worked on this phenomenon before,” Mahadevan said. “Our contribution was not original, but rather to point out certain things that are well-known already to those who know them, and not well-known to others.”

While some may not have noticed or have been bothered by the bunching together of cereal, this effect has played a prominent role in the morning rituals of some students at Harvard.

“It’s annoying because I have to pick up each clinging cheerio one by one,” said David G. Blauvelt ’09. “It’s more work than it’s worth. Actually, the work might be worth it for Honey Nut Cheerios because each cheerio is bursting with flavor, but it’s definitely not worth it for regular cheerios.”

A simple explanation for the “Cheerio Effect,” as such clumping or clinging has been named by scientists, was published by Mahadevan and Vella in the Sept. 15 issue of the American Journal of Physics as part of a pedagogical review done as Vella’s summer project.

“Dominic wanted to work on something that he could talk about at parties, so we worked on this, and others,” said Mahadevan.

At the root of the Cheerio Effect are buoyancy, surface tension, gravity, and the meniscus effect—basic physics concepts.

The buoyancy, or the density of an object compared to the water or air surrounding it, determines whether or not an object will float, according to the research. When an object does float on water, the water will not remain flat, but will instead form a bump or dimple, depending on the object’s weight. When two identical objects float close together, the change is more noticeable—two cheerios, for example, will cause slight dents in the milk and close together, will appear to “fall into” each other or form clumps.

The cheerios on the edge cling to the side of the bowl because the milk tends to dip upward due to the meniscus effect—the attraction between the liquid and the solid.

“This information was already there in the primary literature, in textbooks, but they do not say it correctly or simply,” said Mahadevan. “They say it’s just surface tension, that there’s no weight or gravity involved, which is incorrect.”

Although this natural phenomenon has been explained in multiple settings already, most students still have no idea what causes cereal clumping.

“Yes, I’ve noticed the ‘cheerio effect’ before,” said Charles C. Rinzler ’09. “But I just assumed it happened because of some part of the cheerio that was released when it mixed with milk.”

“I would say it’s Jesus,” said Blauvelt.

Others were more knowledgeable about the subject matter.

“It has to do with adhesion,” said Kathryn A. Giblin ’06.

“It’s simply physics—cheerio magnetization,” said Adam N. Hallowell ’09. “It involves the surface tension of the milk interacting with the physical properties of the cheerios.”

For most students, however, Mahadevan and Vella have clarified an everyday encounter in simple, understandable science terms.

“To quote Samuel Johnson, ‘familiarity doesn’t mean understanding,’” said Mahadevan. “So that’s the beginning and the end: if you see something everyday it doesn’t mean you understand it. We start with the curiosity of a child—many times we failed, once in a while I succeed. Our contribution was merely to wrap our arms around and focus on the simplest aspects of the problem.”