Why do shoelaces suddenly come undone?
The roles of impact and inertia in the failure of a shoelace knot
Engineers filmed shoelaces in slow motion to find out why they suddenly come undone.
One of the researchers ran on a treadmill while a high-speed camera filmed her shoelaces. They also swung laces on a pendulum to separate the stamping from the swinging.
Each footstep loosens the knot, and the whipping lace ends then pull it apart in a sudden, runaway few seconds. The good news: the stronger version of the bow knot holds up much better.
Your laces don’t slowly give up. They spectacularly quit.