What ancient tool serves as the most fundamental, non-coiled expression of energy storage via elasticity?

Answer

The bow and arrow

The bow and arrow, dating back as far as 64,000 years ago, utilized the flexing of a flexible element (the bow) to store energy for propulsion, embodying the core function of a spring.

What ancient tool serves as the most fundamental, non-coiled expression of energy storage via elasticity?
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