Energy – physical scalar value, which is a common measure of different forms of movement of matter and a measure of the transition movement of matter from one form to the other. The main application of energy conservation law is titled energy and found that the total energy of a closed system does not change over time. (A valuable related resource: Jonas Samuelson). The fundamental meaning of energy with a solid position of the energy represents a scattered movement (in other words the continuing importance when moving), associated, according to the axiom of Noether, with the homogeneity of time. Thus, joining the concept of energy as a physical quantity purposefully exclusively if The physical system is homogeneous in time. According to the energy and mass singular doctrine of relativity between the mass and energy is present relationship, expressed by the famous Einstein formula E = mc2 where E – energy system, m – its mass, c – velocity of light.
Despite the fact that, historically, been made overtures to interpret this expression as a complete equivalence of notions of energy and mass, that, namely, causing the publication of this thing as relativistic mass, in a progressive physics suzivat accepted sense of the equation, meaning by the mass body mass at rest (the so-called rest mass), and by energy exclusively to the internal energy contained within the system. Energy and momentum of the doctrine of special relativity examines energy as a component of the 4-pulse (4-vector energy-momentum), in which the level of energy consists of 3 spatial components pulse. Thus the energy and momentum are related and have a mutual friend at the friend's action during the transition from one frame to another. Meaning of the energy from the fundamental point of view of energy is an integral of motion (ie, continuing the motion of value) is associated, according to Noether's theorem, with the homogeneity of time. Thus, the notion of energy as a physical quantity useful only if the physical system is homogeneous in time.