- It can be defined as:
- Mechanical Energy when considering the motion of macroscopic objects. It can be either kinetic energy (energy of motion) or potential energy (stored energy, position).
- Thermal Energy when considering the random motion of microscopic particles of matter: molecules, atoms, ions. It is related to the Internal Energy (microscopic kinetic and potential energy, see First law of Thermodynamics), Enthalpy, Helmholtz free energy, and Gibbs free energy.
- Electrical Energy when considering the motion of charged particules: protons, electrons, ions. It is related to the Electrical Potential Energy(Voltage).
- Radiant Energy (Electromagnetic Radiation) when considering the disturbance of electric and magnetic fields or the motion of photons. It is related to the Relativist Energy and the Quantum Physics Hamiltonian.
- It can be defined as:
See: Mechanical Energy, Thermal Energy, Electrical Energy, Electromagnetic Radiation, Conservation of Energy, Potential Energy, Kinetic Energy, Heat, Thermodynamics, Power, Work, Dark Energy, Internal Energy, Relativistic Energy, Hamiltonian, Enthalpy, Voltage, Hemholtz Free Energy, Gibbs Free Energy, Heat, Pressure, Velocity
- (Wikipedia, 2016) ⇒ https://www.wikiwand.com/en/Energy
- In physics, energy is a property of objects which can be transferred to other objects or converted into different forms. The "ability of a system to perform work" is a common description, but it is difficult to give one single comprehensive definition of energy because of its many forms. For instance, in SI units, energy is measured in joules, and one joule is defined "mechanically", being the energy transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton. Energy (and its units) are often defined in terms of the work they can do. However, technically this is only an approximation, because the second law of thermodynamics means the work a system can do is always less than the total energy of the system, due to waste heat. However, there are many other definitions of energy, depending on the context, such as thermal energy, radiant energy, electromagnetic, nuclear, etc., where definitions are derived that are the most convenient.
- Common energy forms include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature. All of the many forms of energy are convertible to other kinds of energy. In Newtonian physics, there is a universal law of conservation of energy which says that energy can be neither created nor be destroyed; however, it can change from one form to another.
- For "closed systems" with no external source or sink of energy, the first law of thermodynamics states that a system's energy is constant unless energy is transferred in or out by mechanical work or heat, and that no energy is lost in transfer. This means that it is impossible to create or destroy energy. While heat can always be fully converted into work in a reversible isothermal expansion of an ideal gas, for cyclic processes of practical interest in heat engines the second law of thermodynamics states that the system doing work always loses some energy as waste heat. This creates a limit to the amount of heat energy that can do work in a cyclic process, a limit called the available energy. Mechanical and other forms of energy can be transformed in the other direction into thermal energy without such limitations. The total energy of a system can be calculated by adding up all forms of energy in the system.
- (Hyperphysics Encyclopedia, 2005) ⇒ http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html#coneng
- QUOTE: Energy can be defined as the capacity for doing work. It may exist in a variety of forms and may be transformed from one type of energy to another. However, these energy transformations are constrained by a fundamental principle, the Conservation of Energy principle. One way to state this principle is "Energy can neither be created nor destroyed". Another approach is to say that the total energy of an isolated system remains constant.
- (Wolfram Science World, 2005) ⇒ http://scienceworld.wolfram.com/physics/Energy.html
- QUOTE: Energy is an abstract quantity of extreme usefulness in physics because it is defined in such a way that the total energy of any closed physical system is always constant (conservation of energy). It is impossible to overstate the importance of this concept in all branches of physics from elementary mechanics to general relativity. Energy is measured in units of mass times velocity squared, and the MKS and cgs units of energy are the Joule and erg, respectively. Other common units of energy include the Btu, calorie, and kilowatt hour.
- The important quantity in physics known as work, which is the product of applied force over a distance, has units of energy. In fact, the notion that heat is a form of energy was one of the most important developments in classical physics and thermodynamics.
- Energy is related to power [math]P[/math] emitted over a time t by [math]E=Pt[/math].
- (Feynman et al., 1963) ⇒ Richard P. Feynman, Robert B. Leighton and Matthew Sands (1963, 1977, 2006, 2010, 2013) "The Feynman Lectures on Physics": New Millennium Edition is now available online by the California Institute of Technology, Michael A. Gottlieb, and Rudolf Pfeiffer ⇒ http://www.feynmanlectures.caltech.edu/