– Experiment: Thread a ring up through a chain while holding the ring with the thumb and index finger, position the ring such that the ring is perpendicular to the chain and the then drop the ring by releasing one of the two fingers first and then the other

– Intended outcome: The ring would rotate about 90 degrees as it falls. As it rotates more than 90 degrees, the ring has to push the lower end of the chain sideways, which generates a restoring force in the opposite direction of the gravitational force. As a result, the chain forms a knot which holds the ring, preventing it from falling

– Observation: The ring keeps falling to the ground after many drops, not rotating 90 degrees

– Possible point(s) of failure

  • The length and size of chain: The chain may be too short, so the ring doesn’t have enough time to rotate 90 degrees when it falls. Parts of the chain then will not slide up and form a knot around the ring.
  • The stiff of the chain’s links: A chain with small, low-stiffness links will generate less friction than one with larger, stiffer links, thereby accelerating the knot-forming process

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