Shoelaces stay tied because friction and the knot geometry resist the pulling forces of walking.

The longer version

A tied bow holds because the knot jams. Pulling the free ends tightens loops around each other, friction between the laces resists sliding, and the tug of walking pulls in directions that tend to lock the knot rather than undo it. Remove that tension and the same knot comes apart with barely a touch.

The usual bow is a variation on a reef knot, and the difference between the two is simply which way the second crossing goes; the wrong crossing gives a knot that slips and rolls under load. People rarely remember which way they tied it, which is why some bows loosen constantly and others seem to hold for days.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.