Picture this: scientists in a lab at San Diego State University fill a tube with Rice Krispies, slowly crush them with a trash compactor and turn the sounds into music. It's tempting to think academia has finally lost its wits, but these researchers are actually documenting an interesting phenomenon that hadn't been demonstrated before: the song of compression.
A recent study by a SDSU civil engineer professor and his students shows that "highly porous, brittle materials" break down in different ways, depending on the velocity of the compression, or what I'll call Crunch Factor. These materials would include some of our favorite breakfast staples — Rice Krispies, Cocoa Puffs and Cocoa Krispies — and also describes some things that present compaction and disposal issues in the real world; stuff like packing peanuts or the snow after an avalanche. So, knowing how these types of materials react to compaction could have important consequences for engineers.
To get a full picture of what happens when you crunch Rice Krispies and similar materials, the researchers put microphones at the top and bottom of the Krispie-filled tube, then slowly compacted the cereal from the top, down. Based on typical friction experiments, the researchers assumed that, as the piston came down, the top of the cereal would crush, then more cereal below that layer, then more below that layer and on to the bottom. That mimics most of our experiences; picture crushing a car, for example. The car crusher comes down, destroying the top of the car, then the middle of the car, then the bottom. This seems pretty simple and intuitive. However, with porous, brittle materials, the story is entirely different.
The researchers found that, as the grains "popped," the cylinder of Rice Krispies actually divided itself into two parts: the "static zone" and the zone moving at the velocity of the smashing device. However, here's the surprising bit: the static zone is at the bottom, and the moving zone — the one keeping up with the piston — is actually at the top. Watch the video below to see how trippy this looks.
As the smashing continues, the "static zone" at the bottom flows from bottom to top in a repetitious pattern, changing the density of the cereal fragments as it goes. Each cycle consists of one density traveling through the space. The microphones also catch an interesting sound effect: the sound and pressure drop as the static zone reaches the end of one of its cycles.
I would try this experiment myself, but I only eat Cheerios. I'm kind of a cereal monogamist.
"It was the first time anyone had seen a propagating compaction band in granular matter," said Julio Valdes, a civil engineering professor with a low bar for what's beautiful. "We could see it clearly. It was beautiful."
The new research could impact the pharmaceutical industry and disaster response agencies, both of which deal with what scientists are calling "crunchy matter." Their paper has been published in the journal Nature.
Tech Times has reached out to Count Chokula about the study, but the famed cereal tycoon has not yet given a response.