Tom Marzin, a physicist at Cornell University, has created a formula to predict how many times a crêpe or similar flexible material can be folded. The formula hinges on a single number called the elasto-gravity length, balancing gravity and elasticity. He will present the findings on 20 March at the American Physical Society meeting in Denver.
Tom Marzin at Cornell University in Ithaca, New York, developed the formula while on holiday in Brittany, France, where crêpes are popular. He observed that folding a tip of a crêpe causes it to flip back, but larger folds stay due to friction and gravity. This behaviour differs from permanent origami folds, involving instead a 'soft or smooth fold' that is 'just a competition between gravity and elasticity', Marzin says. He will present the results on 20 March at a meeting of the American Physical Society in Denver, Colorado. The key metric is the elasto-gravity length, which incorporates the material's density, stiffness and gravity. Computer models showed it governs folding in various scenarios. To verify, Marzin tested plastic discs, store-bought tortillas and crêpes. He made initial crêpes himself but found thickness inconsistent. 'I didn’t control the thickness well,' he says. 'So I asked my mom to perform the experiments over in France. I asked her to buy the callipers and rulers and a bunch of crêpes from a commercial brand. Those were probably made by a machine, [so] that guarantees a good uniform thickness. And she did it really correctly.' The experiments confirmed predictions. For a 26-centimetre diameter crêpe 0.9 millimetres thick, up to four folds are possible. A same-sized 1.5-mm-thick tortilla, with an elasto-gravity length 3.4 times larger, allows only two folds. 'This length captures all the physics underneath,' Marzin says.
