Untangling the mechanics of knots

Got rope? Then try this experiment: Cross both ends, left over right, then bring the left end under and out, as if tying a pair of shoelaces. If you repeat this sequence, you get what's called a "granny" knot. If, instead, you cross both ends again, this time right over left, you've created a sturdier "reef" knot. The configuration, or "topology," of a knot determines its stiffness. For example, a granny knot is much easier to undo, as its configuration of twists creates weaker forces within the knot, compared with a reef knot. For centuries, sailors have observed such distinctions, choosing certain knots over others to secure vessels - largely by intuition and tradition. Now researchers at MIT and Pierre et Marie Curie University in Paris have analyzed the mechanical forces underpinning simple knots, and come up with a theory that describes how a knot's topology determines its mechanical forces.