It is argued that mechanical action can induce a unique chemical reaction, if enough mechanical energy is concentrated in the bonds involved in the process to bypass the activation energy. This can happen at crack tips, at the core of dislocations, or at the asperities of colliding or sliding surfaces. A mechanical reaction is always complex, as the macroscopic work is distributed among many possible reaction sites. In comparison, an elementary photochemical reaction is induced by a single

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... n, while thermochemical reactions rely on the accidental concentration of energy by thermal uctuations. The paper also compares mechanochemical synthesis in a ball mill with reactions under well-dened loading conditions and mechanochemical experiments carried out on the molecular scale. Closer interaction among those branches of mechanochemistry is urged.