Forms of energy
http://en.wikipedia.org/wiki/Forms_of_energy
From Wikipedia, the free encyclopedia
Thermal energy is energy of microscopic constituents of matter, which may include both kinetic and potential energy.
In the context of physical sciences, several forms of energy have been identified. These include[need quotation to verify]:
| Forms of energy | |
| Type of energy | Description |
| Kinetic | (≥0), that of the motion of a body |
| Potential | A category comprising many forms in this list |
| Mechanical | The sum of (usually macroscopic) kinetic and potential energies |
| Mechanical wave | (≥0), a form of mechanical energy propagated by a material’s oscillations |
| Chemical | that contained in molecules |
| Electric | that from electric fields |
| Magnetic | that from magnetic fields |
| Radiant | (≥0), that of electromagnetic radiation including light |
| Nuclear | that of binding nucleons to form the atomic nucleus |
| Ionization | that of binding an electron to its atom or molecule |
| Elastic | that of deformation of a material (or its container) exhibiting a restorative force |
| Gravitational | that from gravitational fields |
| Intrinsic, the rest energy | (≥0) that equivalent to an object’s rest mass |
| Thermal | A microscopic, disordered equivalent of mechanical energy |
| Heat | an amount of thermal energy being transferred (in a given process) in the direction of decreasing temperature |
| Mechanical work | an amount of energy being transferred in a given process due to displacement in the direction of an applied force |
Some entries in the above list constitute or comprise others in the list. The list is not necessarily complete. Whenever physical scientists discover that a certain phenomenon appears to violate the law of energy conservation, new forms are typically added that account for the discrepancy.
Heat and work are special cases in that they are not properties of systems, but are instead properties of processes that transfer energy. In general we cannot measure how much heat or work are present in an object, but rather only how much energy is transferred among objects in certain ways during the occurrence of a given process. Heat and work are measured as positive or negative depending on which side of the transfer we view them from.
Classical mechanics distinguishes between kinetic energy, which is determined by an object’s movement through space, and potential energy, which is a function of the position of an object within a field, which may itself be related to the arrangement of other objects or particles. These include gravitational energy (which is stored in the way masses are arranged in a gravitational field), several types of nuclear energy (which utilize potentials from the nuclear force and the weak force), electric energy (from the electric field), and magnetic energy (from the magnetic field).
Other familiar types of energy are a varying mix of both potential and kinetic energy. An example is mechanical energy which is the sum of (usually macroscopic) kinetic and potential energy in a system. Elastic energy in materials is also dependent upon electrical potential energy (among atoms and molecules), as is chemical energy, which is stored and released from a reservoir of electrical potential energy between electrons, and the molecules or atomic nuclei that attract them.[need quotation to verify].
Potential energies are often measured as positive or negative depending on whether they are greater or less than the energy of a specified base state or configuration such as two interacting bodies being infinitely far apart.
Wave energies (such as radiant or sound energy), kinetic energy, and rest energy are each greater than or equal to zero because they are measured in comparison to a base state of zero energy: “no wave”, “no motion”, and “no inertia”, respectively.
It has been attempted to categorize all forms of energy as either kinetic or potential, but as Richard Feynman points out:
These notions of potential and kinetic energy depend on a notion of length scale. For example, one can speak of macroscopic potential and kinetic energy, which do not include thermal potential and kinetic energy. Also what is called chemical potential energy is a macroscopic notion, and closer examination shows that it is really the sum of the potential and kinetic energy on the atomic and subatomic scale. Similar remarks apply to nuclear “potential” energy and most other forms of energy. This dependence on length scale is non-problematic if the various length scales are decoupled, as is often the case … but confusion can arise when different length scales are coupled, for instance when friction converts macroscopic work into microscopic thermal energy.
Also, at relativistic speeds, defining kinetic energy is problematic because the energy due to the body’s motion does not simply contribute additively to the total energy as it does at classical speeds.
Energy may be transformed between different forms at various efficiencies. Items that transform between these forms are called transducers.
