Crumpled cream.
CREDIT: R. EMMANUEL DE SOUZA/FEDERAL UNIVERSITY OF PERNAMBUCO |
Colleagues of Marcelo A. F. Gomes, a physicist at the Federal University of Pernambuco in Recife, Brazil, can fairly accuse him of skimming the cream off the top in his research. In an unusual experiment, Gomes and his team have studied how films of cream that form on heated milk crumple when they are hoisted from the liquid and set down on a glass plate.
Even as a child, Gomes says, he was fascinated by the films on his café au lait, which would crumple whenever he tried to pluck them off. Others have studied how paper and polymer sheets crumple, Gomes says, but cream is different: The film is so flimsy it will wad up under its own weight.
The wads are neither two-dimensional sheets nor three-dimensional solids. By measuring them and peering inside with nuclear magnetic resonance, the researchers found that the wads have a "fractal" dimension of about 2.5, as they report in the 21 June issue of the Journal of Physics D. Because that dimension is the same as that for crumpled paper, the experiment shows that what matters is not how you squash the wads but how their creases and crinkles fit together, says Sahraoui Chaieb, a physicist at the University of Illinois, Urbana-Champaign: "It's all geometry."
