Stories from Physics for 11-14 14-16
Researchers have investigated the causes of shoelaces coming untied during walking. A team from the University of California at Berkeley used slow-motion video footage to examine how shoelaces come undone. They report that the striking of the shoe against the ground initially serves to loosen the knot and the whipping motion of the ends of the laces causes the knot to slip. The peak acceleration of the knot was found to be 7 g – similar to that experienced by the Apollo spacecraft during re-entry. The data showed that knot failure happened suddenly, with little warning, within a few impact cycles.