APS 2008: Crumpled balls
Some physics experiments are just patently fun -- the science seems to sneak in by stealth, changing the way you view ordinary objects. Take crumpled balls, for example. An unassuming object with an extraordinarily complex shape. The path to get from an almost two-dimensional sheet to a three-dimensional object involves many energetic choices – whether it’s more efficient to fold in one direction or stretch in another. Understanding how crumpling happens has the potential to illuminate a lot of interesting physics about how folding happens in nature.
On Monday, Dominique Cambou presented the first results of a ostensibly simple project: mapping the 3D structure of a crumpled ball of aluminum foil. Cambou, a graduate student in Narayanan Menon's lab, systematically crumples balls and then subjects them to x-rays to image their internal structure.
Analysis is still in its early stages, but Cambou says she has already observed some interesting patterns.
The density of foil, for example, seems to be highest close to the surface. There seems to be something that inhibits folding closer to the center of the sheet. "It seems counterintuitive to me, since the entire sheet is connected," says Cambou. There also seems to be an unusual amount of layering in the foil.
Here's a picture of a reconstructed cross-section of a foil ball. The lines show the foil passing through the plane; the thinner the line, the more perpendicular the foil.
Eventually Cambou says she hopes to link the final shape of the balls to the complex energetic path a sheet takes to achieve its final conformation.