I was wondering why V is a common symbol for voltage. The symbol is not named after the unit volt, because it is older than the volt unit, which dates from 1874. Before that, voltage was potential. In 1828 Green used the symbol V for the potential function which he introduced in his essay on electricity. In 1785 Laplace used the symbol V for M/r, in his Théorie des attractions. Laplace used V without giving it a name, but to us it is the gravitational potential except for a constant. In 1788, Lagrange expressed conservation of vis viva (living force, energy) as T+V = const, with T=1/2 m v2. (Méc. analytique) So now I am wondering if the symbol V is named after vis viva.