In physics, energy (Ancient Greek: ἐνέργεια energeia "activity, operation") is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems. However, this must be understood as an overly simplified definition, as the laws of thermodynamics demonstrate that not all energy can perform work. Depending on the boundaries of the physical system in question, energy as understood in the above definition may sometimes be better described by concepts such as exergy, emergy and thermodynamic free energy. Therefore, in the words of Richard Feynman, "It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount." However, it is clear that energy is always an indispensable prerequisite for performing work, and the concept has great importance in natural science.
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Some articles on energy:
... One form of energy can often be readily transformed into another with the help of a device- for instance, a battery, from chemical energy to electric energy a dam gravitational potential energy ... the case of a chemical explosion, chemical potential energy is transformed to kinetic energy and thermal energy in a very short time ... At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum ...
... The U term can be interpreted as the energy required to create the system, and the pV term as the energy that would be required to "make room" for the system if the pressure of the environment remained constant ... pressure p and temperature T, is created or brought to its present state from absolute zero, energy must be supplied equal to its internal energy U plus pV, where pV is ... to study the internal properties of the system and therefore the internal energy is used ...
... caused by a combination of excessive food energy intake, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrine ... to a slow metabolism is limited on average obese people have a greater energy expenditure than their thin counterparts due to the energy required to ... be improved by reducing the consumption of energy-dense foods such as those high in fat and sugars, and by increasing the intake of dietary fiber ...
... Internal energy, U, must be supplied to remove particles from a surrounding in order to allow space for the creation of a system, providing that environmental variables, such as ... This internal energy also includes the energy required for activation and the breaking of bonded compounds into gaseous species ... process is calculated within enthalpy calculations as U + pV, to label the amount of energy or work required to "set aside space for" and "create" the system describing ...
More definitions of "energy":
- (noun): (physics) the capacity of a physical system to do work; the units of energy are joules or ergs.
Example: "Energy can take a wide variety of forms"
- (noun): The federal department responsible for maintaining a national energy policy of the United States; created in 1977.
Synonyms: Department of Energy, Energy Department, DOE
- (noun): An imaginative lively style (especially style of writing).
Example: "His writing conveys great energy"
Synonyms: vigor, vigour, vim
Famous quotes containing the word energy:
“The flattering, if arbitrary, label, First Lady of the Theatre, takes its toll. The demands are great, not only in energy but eventually in dramatic focus. It is difficult, if not impossible, for a star to occupy an inch of space without bursting seams, cramping everyone elses style and unbalancing a play. No matter how self-effacing a famous player may be, he makes an entrance as a casual neighbor and the audience interest shifts to the house next door.”
—Helen Hayes (19001993)
“But often the presence of mind and energy of a person remote from the spotlight decide the course of history for centuries to come.”
—Stefan Zweig (18811942)
“Children are intensely invested in getting their way. They will devote more emotional and intellectual energy to winning arguments than parents ever will, and are almost always better rested.”
—Jean Callahan (20th century)