measure for the ability of a system to do work
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Energy is a fundamental concept in physics that is often defined as the capacity to do mechanical work — a definition disputed by many physicists. It also has a specific connotation of the forms of energy used for powering technological society.


  • Our decision about energy will test the character of the American people and the ability of the President and the Congress to govern this Nation. This difficult effort will be the "moral equivalent of war," except that we will be uniting our efforts to build and not to destroy.
    • Jimmy Carter, address to the nation on the energy problem (April 18, 1977); Public Papers of the Presidents of the United States: Jimmy Carter, 1977, book 1, p. 656. Carter was quoting William James, who used the phrase in his essay, "The Moral Equivalent of War".
  • It is found that the sum of energy of motion and energy of position is always constant. ...Energy is a quantity which can be greater or less but has no direction. ...[E]nergy is conserved, or is indestructible. This form of speech might be applied to other cases of alternate immortality, where one of two things comes into existence on disappearance of the other.
  • E = mc²
    • Albert Einstein, The equivalence of matter and energy was originally expressed by the equation m = L/c², which easily translates into the far more well known E = mc² in Does the Inertia of a Body Depend Upon Its Energy Content? published in the Annalen der Physik (27 September 1905) : "If a body gives off the energy L in the form of radiation, its mass diminishes by L/c²."
  • It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount.
  • We must proceed with our own energy development. Exploitation of domestic petroleum and natural gas potentialities, along with nuclear, solar, geothermal, and non-fossil fuels is vital. We will never again permit any foreign nation to have Uncle Sam over a barrel of oil.
    • Gerald Ford, speech to the Anti-Defamation League of B'nai B'rith, West Palm Beach, Florida (January 26, 1974); reported in Congressional Record (February 4, 1974), vol. 120, p. 2044.
  • The real key word that triggers my rage is the word "energy". When people start talking about positive or negative types, for instance, negative energy — what are you talking about? What do you mean? Let's think about it, what does energy mean? Well, we know what it means, you know, energy from petrol when it's burned and moves a car and makes it move, it's like this. "This room has positive energy." Now, where the fuck is it going, then? It's not moving. It's covering up such woolly thinking, such pathetic nonsense.
    • Stephen Fry on New Age use of the word "energy".
    • Room 101, Season 6 Episode 10
  • The impetuosity of youth becomes energy in manhood.
  • If you take a bale of hay and tie it to the tail of a mule and then strike a match and set the bale of hay on fire, and if you then compare the energy expended shortly thereafter by the mule with the energy expended by yourself in the striking of the match, you will understand the concept of amplification.

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