In last week’s post, we finished up by learning of Sadi Carnot’s eventual recognition that the phenomenon of heat relates to the smallest-scale motions of matter. I’ll start the last stage in our historical overview by introducing the term energy itself for the first time.Note 1 Up until early in the nineteenth century, the name ‘living force’ prevailed in relation to the quantity mv², the product of a body’s mass and the square of its speed. Then in 1807, in A Course of Lectures in Natural Philosophy and the Mechanical Arts, Thomas Young (1773-1829) proposed the term ‘energy’ as an alternative to ‘living force’.Note 2 It’s noteworthy that in doing so, Young was not interested in whether this energy had some sort of metaphysical significance i.e. whether it had some sort of inherent existence. Rather, he was interested in the observation that in many physical situations, characteristic effects are proportional to this quantity, that it arises as an invariant feature of certain physical situations.[2] Continue reading →