sentences:  History of energy
  
  The word energy derives from Greek "ἐνέργεια" ("energeia"), which appears for the first time in the 4th century BCE works of Aristotle (OUP V, 240, 1991) (including Physics, Metaphysics, Nicomachean Ethicsand De Anima).The modern concept of energy emerged from the idea of "vis viva" (living force), which Leibniz defined as the product of the mass of an object and its velocity squared; he believed that total "vis viva" was conserved.