Energy
Example: In a plant that furnishes pumped-storage hydroelectricity, mechanical work and electrical work is done by machines like electric pumps and electrical generators. The pumped water stores mechanical work. The amount of energy put into the system equals the amount of energy which comes out of the system, less that amount of energy used to overcome friction.
Such examples suggested the derivation of some unifying concepts: Instead of discerning (transferred) forms of work or stored work, there has been introduced one single physical quantity called energy. Energy is assumed to have substance-like qualities; energy can be apportioned and transferred. Energy cannot be created from nothing, or to be annihilated to nothing, thus energy becomes a conserved quantity, when properly balanced.
Describing the transfer of energy two dictions, two ways of wording are used:
(energy carriers exchanging energy) Physical interactions occur by carriers (linear momentum, electric charge, entropy) exchanging energy. For example, a generator transfers energy from angular momentum to electric charge.
(energy forms transforming energy) Energy forms are transformed; for example mechanical energy into electrical energy by a generator.
Often the energy value results from multiplying two related quantities: (a generalized) potential (relative velocity, voltage, temperature difference) times some substance-like quantity (linear momentum, electrical charge, entropy). — Thus energy has to be measured by first choosing a carrier/form. The measurement usually happens indirectly, by obtaining two values (potential and substance-like quantity) and by multiplying their values.
- (see any measurement device for energy below)
For the ranges of energy-values see: Orders of magnitude (energy)
Read more about this topic: Measuring Instrument
Famous quotes containing the word energy:
“Reckoned physiologically, everything ugly weakens and afflicts man. It recalls decay, danger, impotence; he actually suffers a loss of energy in its presence. The effect of the ugly can be measured with a dynamometer. Whenever man feels in any way depressed, he senses the proximity of something “ugly.” His feeling of power, his will to power, his courage, his pride—they decline with the ugly, they increase with the beautiful.”
—Friedrich Nietzsche (1844–1900)
“The scholar may be sure that he writes the tougher truth for the calluses on his palms. They give firmness to the sentence. Indeed, the mind never makes a great and successful effort, without a corresponding energy of the body.”
—Henry David Thoreau (1817–1862)
“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)