# 19247

In this article, I read that an orb of a given size, when slightly flattened, will pack more densely than when perfectly round. No kidding? Do you suppose if we were to crush cars into little cubes we could hurl more into a landfill than we could just by driving them over a cliff? What am I missing?

*Marc GurevitchNicholasville, Ky.*

*Don’t be misled by how many cars might fill a landfill, says Salvatore Torquato of Princeton University. Rather, consider the pile that either whole or crushed cars would form. The M&M team explored what fraction of such a pile is solid material, not air. When deformed spheres such as M&Ms are randomly piled and jostled, their small variations from sphericity boost that fraction unexpectedly high*.—P. Weiss Your story states that “each tight-packed sphere typically has only 6 adjacent neighbors.” However, it is well known that closely packed oranges touch 12 adjacent oranges (cubic closest packing). One is tempted to explain the apparent 2-fold discrepancy by considering that each contact is shared by two particles, but that would be wrong. The number of contacting neighbors actually does decrease to about six in randomly close-packed spheres.

*Don GarlickHumboldt State UniversityArcata, Calif.*