“It is scientific curiosity,” said Oliver O'Reilly, a professor of mechanical engineering at UC Berkeley.
For more than two years, O'Reilly and mechanical engineering graduate students Christine Gregg and Christopher Daily-Diamond have studied the phenomenon of shoelaces becoming untied.
If the topic sounds simple, consider the factors:
“Your walking stride, your shoelace material,” said O'Reilly.
“How is it tied?” said Gregg.
“We have friction. We have the side [of the shoe]. We have the shape, how it's tied,” said Daily-Diamond.
“What’s the material of the lace? What are your shoes made out of?” added Gregg.
The team spent more than two years studying “dynamic untying,” as they called it, testing different varieties of the typical bow knot in both the weak and strong configurations. Gregg walked and ran countless miles on Berkeley streets, then even more on a treadmill.
With a slow motion camera they captured and duplicated the forces that slowly break pull even the strongest knots to failure. Untied laces are not a a matter of human error; It’s physics, with possible future applications that might even help us understand DNA.
The study concludes that impact forces loosen the knot and then the inertial force on the free ends of the laces of the swinging leg can cause complete unraveling within two strides.