Knotty Nemesis

The Friday File: At last, engineers have figured out how shoelace bows come undone! There are two forces at work. The to-and-fro movement of the leg and the impact of the shoe hitting the ground. Turns out neither force is strong enough alone to unravel the knot. These forces could theoretically tighten the bow, but don’t. After reading the paper, my suggestion is long bows and short free ends.