Crumpling is a ubiquitous, though poorly understood, physical phenomenon. It occurs when a fender absorbs the energy of a car crash, when Earth’s crust buckles at the interface between colliding tectonic plates to create a mountain range, when a blood cell’s membrane folds to allow the cell to pass through a narrow capillary, when a grape shrivels to a raisin as it dries out, and when a storage tank collapses.
It takes energy to crumple a sheet–to force it uniformly into a smaller and smaller ball. Where does that energy go?