ABSTRACT
Feynman, Richard Leighton, R.B. Sands, M. There is a fact, or if you wish, a law governing all natural phenomena that are known to date. There is no known exception to this law-it is exact as far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity which does not change when something happens.
