Understanding Energy: Concepts, Types, and Conservation
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The Concept of Energy in Physics
In physics, the universal law of conservation of energy, which is the basis for the first law of thermodynamics, indicates that the energy attached to an isolated system remains constant over time. However, the theory of special relativity establishes an equivalence between mass and energy by which all bodies, by virtue of being formed of matter, contain energy. Moreover, additional energy may be conceptually divided into several types according to the properties of the system being considered. For example, kinetic energy is quantified by the motion of matter, chemical energy by the chemical composition, potential energy depending on properties such as the state of deformation or the position of matter in relation to the forces acting on it, and thermal energy as the thermodynamic state.
Energy is not a real physical state, no “intangible” substance, but only a scalar quantity that is assigned to the state of the physical system. That is, energy is a mathematical abstraction tool or a property of physical systems. For example, one can say that a system with zero kinetic energy is at rest.
It is used as an abstraction of physical systems for the facility to work with scalar quantities, compared with vector quantities such as speed or position. For example, in mechanics, one can fully describe the dynamics of a system in terms of the kinetic and potential energy, comprising the mechanical energy, which in Newtonian mechanics has retained ownership, that is, be invariant over time.
Mathematically, the conservation of energy for a system is a direct consequence of the evolution equations of this system being independent of the instant of time considered, according to Noether’s theorem.
Energy in Different Types of Physical Systems
Energy is also a physical quantity which takes various forms, is involved in all processes of change of physical state, is transformed and transmitted, depends on the fixed reference system and it is conserved [1]. Therefore, any body can possess energy, thanks to its movement, its chemical composition, its position, its temperature, its mass and some other properties. In the various disciplines of physics and science, there are several definitions of energy, of course, all consistent with and complement each other, each always related to the concept of work.
Classical Physics
The mechanics are:
- Mechanical energy, which is the combination or sum of the following types:
- Kinetic energy: energy of motion.
- Potential energy: energy associated with the position within a conservative force field. For example, is the gravitational potential energy and elastic potential energy (or strain energy, so named because of the elastic deformation). A wave is also capable of transmitting energy to move through an elastic medium.
In electromagnetism we have:
- Electromagnetic energy, which consists of:
- Radiant energy: the energy possessed by electromagnetic waves.
- Heat energy: the amount of energy that a unit mass of matter can give off when a chemical reaction occurs from oxidation.
- Electric potential energy (see electric potential)
- Electricity: result of the existence of a potential difference between two points.
The thermodynamics are:
- Internal energy, which is the sum of the mechanical energy of the constituent particles of a system.
- Thermal energy, energy released as heat, obtained from nature (geothermal energy) by burning.