“Total energy, which is the conserved quantity, is the sum of several terms: kinetic energy, mass energy, potential energy, and field energy. Those different terms refer to aspects of reality that seem, on the face of it, quite different. Much of the power of the concept of energy, in applications, comes precisely from its ability to describe, and relate, several different aspects of reality.”

“Total energy, which is the conserved quantity, is the sum of several terms: kinetic energy, mass energy, potential energy, and field energy. Those different terms refer to aspects of reality that seem, on the face of it, quite different. Much of the power of the concept of energy, in applications, comes precisely from its ability to describe, and relate, several different aspects of reality.”

— Frank Wilczek