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Feeling snappy - The ultrafast snap of a finger is mediated by skin friction
Despite being a near universal motion that humans have performed for centuries, the physics of a finger snap remain unexplored. By combining experiments and simulations, we show that human finger pads have an optimally tuned friction and compressibility which allow the finger snap to reach some of the highest angular accelerations observed in the human body. We find that the skin friction plays a dual role as a `latch’ in the ultrafast motion of a finger snap: maximizing the potential energy stored, while minimizing the energy dissipated by quickly releasing for a rapid motion.