Shoe-string theory: science shows why shoelaces come untied

When running, the acceleration forces on a shoelace knot are higher than that experienced by the human body on the most extreme rollercoaster

1

2

3

Running

motion

Foot hits ground

Leg swing

A running foot strikes the ground at seven times the force of gravity, causing the free end of the laces to stretch and then relax ...

Free

end

Loop

... as the knot loosens, the swinging leg applies an inertial force on the free ends of the laces ...

Inertial

forces

... which rapidly leads to a failure of the knot in as few as two strides after inertia acts on the laces

Knot loosens

under forces

When running, the acceleration forces on a shoelace knot are higher than that experienced by the human body on the most extreme rollercoaster

1

2

3

Running motion

Leg

swing

Foot hits

ground

A running foot strikes the ground at seven times the force of gravity, causing the free end of the laces to stretch and then relax ...

... as the knot loosens, the swinging leg applies an inertial force on the free ends of the laces ...

... which rapidly leads to a failure of the knot in as few as two strides after inertia acts on the laces

Knot loosens

under forces

Inertial

forces

Free

end

Loop