Energy
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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Famous quotes containing the word energy:
“The principle of avoiding the unnecessary expenditure of energy has enabled the species to survive in a world full of stimuli; but it prevents the survival of the aristocracy.”
—Rebecca West (1892–1983)
“His eloquence was of every kind, and he excelled in the argumentative as well as in the declamatory way. But his invectives were terrible, and uttered with such energy of diction, and stern dignity of action and countenance, that he intimidated those who were the most willing and the best able to encounter him. Their arms fell out of their hands, and they shrunk under the ascendant which his genius gained over theirs.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“Because humans are not alone in exhibiting such behavior—bees stockpile royal jelly, birds feather their nests, mice shred paper—it’s possible that a pregnant woman who scrubs her house from floor to ceiling [just before her baby is born] is responding to a biological imperative . . . . Of course there are those who believe that . . . the burst of energy that propels a pregnant woman to clean her house is a perfectly natural response to their mother’s impending visit.”
—Mary Arrigo (20th century)