Asked by: Saul Parsons, Leicester
The ability of shoelaces to work themselves free is one of life's little irritations. But as a team at the University of California, Berkeley, showed last year, it's actually the result of some surprisingly strong forces.
The repeated impact of our shoes on the floor generates forces of up to seven times that of gravity, which loosen the knot. Then the swinging motion of our legs creates swishing forces that cause the laces to slide apart. The team found that one way to reduce this is using a so-called square knot: first cross the laces and thread one under the other as normal, but then form the bow by crossing and threading the laces in the opposite direction.
Robert is a science writer and visiting professor of science at Aston University.