Energy transformation

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In physics, the term [energy] describes the amount of work which may potentially be done by forces within a system. Changes in energy in systems can only be accomplished by adding or subtracting energy from them, as energy is a quantity which is conserved. (Loosely, changes in the energy of systems also coincide with changes in the system's mass).

Energy in a system may be transformed so that it resides in a different state. Energy in many states may be used to do many varieties of physical work. Energy may be used in natural processes or machines, or else to provide some service to society (such as heat, light, or motion). For example, an internal combustion engine converts the potential chemical energy in gasoline and oxygen into heat, which is then transformed into the propulsive energy (kinetic energy that moves a vehicle. A solar cell converts solar radiation into electrical energy that can then be used to light a bulb or power a computer.

The generic name for a device which converts energy from one form to another is transducer.

Contents 1 History of energy transformation from the early universe 2 Examples of sets of energy conversions in machines 3 Other energy conversions 4 See also

[edit] History of energy transformation from the early universe

Energy transformations in the universe over time are generally characterized by various kinds of potential energy which has been available since the Big Bang, later being "released" (transformed to more active types of energy such as kinetic or radiant energy), when a triggering mechanism is available.

Familiar examples of such processes include nuclear decay, in which energy is released which was originally "stored" in heavy isotopes (such as uranium and thorium), by nucleosynthesis, a process which ultimately uses the gravitational potential energy released from the gravitational collapse of supernovae, to store energy in the creation of these heavy elements before they were incorporated into the solar system and the Earth. This energy is triggered and released in nuclear fission bombs. In a slower process, heat from nuclear decay of these atoms in the core of the Earth releases heat, which in turn may lift mountains, via orogenesis. This slow lifting represents a kind of gravitational potential energy storage of the heat energy, which may be released to active kinetic energy in landslides, after a triggering event. Earthquakes also release stored elastic potential energy in rocks, a store which has been produced ultimately from the same radioactive heat sources. Thus, according to present understanding, familiar events such as landslides and earthquakes release energy which has been stored as potential energy in the Earth's gravitational field or elastic strain (mechanical potential energy) in rocks; but prior to this, represents energy that has been stored in heavy atoms since the collapse of long-destroyed stars created these atoms.

In other similar chain of transformations beginning at the dawn of the universe, nuclear fusion of hydrogen in the Sun releases another store of potential energy which was created at the time of the Big Bang. At that time, according to theory, space expanded and the universe cooled too rapidly for hydrogen to completely fuse into heavier elements. This meant that hydrogen represents a store of potential energy which can be released by fusion. Such a fusion process is triggered by heat and pressure generated from gravitational collapse of hydrogen clouds when they produce stars, and some of the fusion energy is then transformed into sunlight. Such sunlight from our Sun may again be stored as gravitational potential energy after it strikes the Earth, as (for example) water evaporates from oceans and is deposited upon mountains (where, after being released at a hydroelectric dam, it can be used to drive turbine/generators to produce electricity). Sunlight also drives many weather phenomena, save those generated by volcanic events. An example of a solar-mediated weather event is a hurricane, which occurs when large unstable areas of warm ocean, heated over months, give up some of their thermal energy suddenly to power a few days of violent air movement. Sunlight is also captured by plants as chemical potential energy, when carbon dioxide and water are converted into a combustible combination of carbohydrates, lipids, and oxygen. Release of this energy as heat and light may be triggered suddenly by a spark, in a forest fire; or it may be available more slowly for animal or human metabolism, when these molecules are ingested, and catabolism is triggered by enzyme action. Through all of these transformation chains, potential energy stored at the time of the Big Bang is later released by intermediate events, sometimes being stored in a number of ways over time between releases, as more active energy. In all these events, one kind of energy is converted to other types of energy, including heat.

[edit] Examples of sets of energy conversions in machines

For instance, a coal-fired power plant involves these power transfers:

1. Chemical energy in the coal converted to thermal energy
2. Thermal energy converted to kinetic energy in steam
3. Kinetic energy converted to mechanical energy in the turbine
4. Mechanical energy of the turbine converted to electrical energy, which is the ultimate output

In such a system, the last step is almost perfectly efficient, the first and second steps are fairly efficient, but the third step is relatively inefficient.

In a conventional automobile, these power transfers are involved:

1. Potential energy in the fuel converted to kinetic energy of expanding gas via combustion
2. Kinetic energy of expanding gas converted to linear piston movement
3. Linear piston movement converted to rotary crankshaft movement
4. Rotary crankshaft movement passed into transmission assembly
5. Rotary movement passed out of transmission assembly
6. Rotary movement passed through differential
7. Rotary movement passed out of differential to drive wheels
8. Rotary movement of drive wheels converted to linear motion of the vehicle.

[edit] Other energy conversions

There are many different machines and transducers that convert one energy form into another. A short list of examples follows:

• Thermoelectric (Heat → Electricity)
• Geothermal power (Heat→ Electricity)
• Heat engines, such as the internal combustion engine used in cars, or the steam engine (Heat → Mechanical energy)
• Ocean thermal power (Heat → Electricity)
• Hydroelectric dams (Gravitational potential energy → Electricity)
• Electric generator (Kinetic energy or Mechanical work → Electricity)
• Fuel cells (Chemical energy → Electricity)
• Lamp (Chemical energy → Heat and Light)
• Microphone (Sound → Electricity)
• Nuclear reactor (Nuclear energy → Heat)
• Nuclear power plant (Nuclear energy → Heat → Electricity)
• Fossil fuel power plant (Chemical energy → Heat → Electricity)
• Solar cells (Light → Electricity), including downconversion and upconversion
• Solar thermal (Light → Heat)
• Wave power (Mechanical energy → Electricity)
• Windmills (Wind energy → Electricity or Mechanical energy)
• Piezoelectrics (Strain → Electricity)
• Acoustoelectrics (Sound → Electricity)
• Friction (Kinetic energy → Heat)

[edit] See also