For Helmholtz, this type of analysis enabled very different-seeming phenomena—gravity, motion, electricity—to be related to each other quantitatively. Every type of energy has a “best possible” exchange rate into another form of energy, which is embedded in the laws of nature. Helmholtz also introduced another important idea in his paper, which today is called potential energy but which he referred to as tensional forces. In simple terms, this means that energy can be stored and released later.
