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Physics

Bistable Spring Mechanisms in Slap Bracelets

Quick fact

A slap bracelet is a pre-stressed cylindrical shell with a curved cross-section. This geometry creates two stable shapes—straight and coiled—between which it can snap through when a small force overcomes an energy barrier.

Why this is interesting

Why does a slap bracelet snap from a straight strip into a tight coil around your wrist with just a light tap? The secret lies in its built-in tension and curved cross-section.