In this paper, I will examine John Smeaton’s contribution to the vis viva controversy in Britain, focusing on how the hybridization of science, technology, and industry helped to establish vis viva, or mechanic power, as a measure of motive force. Smeaton, embodying the ‘hybrid expert’ who combined theoretical knowledge and practical knowhow, demonstrated that the notion of vis viva possessed a greater explanatory power than momentum, because it could be used to explain the difference in efficiency between overshot and undershot (...) waterwheels. Smeaton’s conclusions were correct since waterwheel efficiency was already measured in terms that were proportional to vis viva, not momentum, as a result of the industrial applications of waterwheel technology, which favored measuring efficiency by the product of mass and vertical displacement. Toward the end of the eighteenth century, the loss of motive force in the inelastic collision driving the undershot wheel began to be seen as equivalent to the expenditure of labor in the manufacture of commodities, further underlining how strictly scientific conclusions about motive force could have their origin in industrial practices. (shrink)