From: veritasium
A demonstration involves a metal ring and a closed loop of chain [00:03:12].
Expected Outcome
When a metal ring is held over a dangling chain and then dropped, it naturally falls off [00:03:29]. This is the expected result because both the ring and the chain are closed loops [00:03:38].
The Perplexing Trick
Despite the seemingly obvious outcome, it is possible to make the metal ring “stick” onto the chain [00:03:47], [00:03:54].
How the Trick is Performed
The key to getting the ring to stick on the chain is to release it on one side before the other [00:04:32]. For instance, releasing it with the thumb first, allowing it to slide off the finger [00:04:39], [00:04:43].
The Physics Behind It
The asymmetrical release introduces a slight rotation to the ring [00:04:51]. This causes the ring to rotate approximately 90 degrees as it slides down the chain [00:04:54]. As the ring descends, segments of the chain slide up its sides [00:05:03]. At the bottom, the lowest piece of the chain appears to be drawn into the middle of the ring, then pulled around, causing it to snap and lock into place [00:05:07], [00:05:12], [00:05:13], [00:05:17].