Last updated May 24, 2017 at 1:00 pm
Surely a question that has consumed us all at one time or another: why do shoe laces come undone? A team of mechanical engineers at the University of California Berkeley decided to check it out.
Turns out that, for shoe laces, it’s a combination of the stomping forces when your foot hits the ground and the whipping force when you swing your leg through the air to take a stride. The stomping loosens the knot while the whipping unravels it. They worked this out by analysing videos taken with slow-motion cameras.
Once done with failing footwear, the team turned their attention to nuisance neck ties. They noted that there are two ways to tie a bow tie and one is stronger than the other. The strong knot is based on a reef knot where two crossings are of opposite handedness while the weak knot is based on a slip knot where the two crossings have the same handedness. They found that, while the stronger tie did indeed resist failure for longer than the weak knot, both eventually failed in the same way.
Researcher Oliver O’Reilly whose lab conducted the research observed “We were able to show that the weak knot will always fail and the strong knot will fail at a certain time scale, but we still do not understand why there’s a fundamental mechanical difference between those two knots.”
While this research may seem quaint in an age of Velcro tabs, slip-on shoes and ready-made bow ties, O’Reilly notes that very little research has been conducted into the mechanics of knots and their failure. So, perhaps, this is the beginning of a research effort to better understand knots and how they work. Or don’t.
Image: An overhead view of the tying of the weak knot (on the left of each image panel) and the tying of the strong knot (on the right of each image panel). Note, the two knots only differ in the relative tying of the second trefoil to the first trefoil. © Daily-Diamond et al
- Link to original research article: http://rspa.royalsocietypublishing.org/content/473/2200/20160770
Thumbnail image credit: Diamond et al