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. 2017 Apr 12;473(2200):20160770. doi: 10.1098/rspa.2016.0770

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© 2017 The Authors.

Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

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Figure 3. — Static representation of hypothesized stages of knot failure. (a) Terminology for various parts of the knot. (b) As the leg is swung backwards to impact the ground, the inertia of the free ends and loops pull open the centre of the knot. If the free end and loops are approximately the same length, these forces will be comparable. If the knot centre is tightened, frictional forces will somewhat ameliorate the inertial force imbalance. (c) Repeated impact causes the centre of the knot to incrementally loosen which reduces frictional effects and magnifies the effects of the inertial imbalance between the free ends and loops. Additionally, the impact excitation causes slight pull through of the free end. This increases the inertial effects of the free end, enabling further free-end pull through. (d) Eventually, the inertial effect of the free end is sufficiently large that the knot fails suddenly and catastrophically when the free end is completely pulled through the centre of the knot, resulting in complete failure of the second trefoil. (Online version is colour.)