energy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The capacity for work or vigorous activity; vigor; power. See Synonyms at strength.
2. n. Exertion of vigor or power: a project requiring a great deal of time and energy.
3. n. Vitality and intensity of expression: a speech delivered with energy and emotion.
4. n. Usable heat or power: Each year Americans consume a high percentage of the world's energy.
5. n. A source of usable power, such as petroleum or coal.
6. n. Physics The capacity of a physical system to do work.

Century Dictionary and Cyclopedia

1. n. The actual exertion of power; power exerted; strength in action; vigorous operation.
2. n. Activity considered as a characteristic; habitual putting forth of power or strength, physical or mental, or readiness to exert it.
3. n. The exertion of or capacity for a particular kind of force; action or the power of acting in any manner; special ability or agency: used of the active faculties or modes of action regarded severally, and often in the plural: as, creative energy; the energies of mind and body.
4. n. In the Aristotelian philos., actuality; realization; existence; the being no longer in germ or in posse, but in life or in esse: opposed to power, potency, or potentiality. Thus, first energy is the state of acquired habit; second energy, the exercise of a habit: one when he has learned to sing is a singer in first energy; when he is singing, he is a singer in second energy. See act.
5. n. A fact of acting or actually being.
6. n. In rhetoric, the quality of awakening the imagination of the reader or hearer, and bringing the meaning of what is said home to him; liveliness.
7. n. In physics: Half the sum of the masses of the particles of a system each multiplied by the square of its velocity; half the vis viva. See vis viva. This sense, introduced by Dr. Thomas Young, is now obsolete. It gave rise to the following, which was introduced about 1850 by Sir William Thomson, and is now widely current.
8. n. Half the greatest value to which the sum of the masses of all the particles of a given system each multiplied by the square of its velocity, could attain except for friction, viscosity, and other forces dependent on the velocities of the particles; otherwise, the amount of work (see work) which a given system could perform were it not for resistance dependent on the velocities. The law of energy is precisely the principle that these two definitions are equivalent. This law applies solely to forces dependent alone on the relative positions of particles—that is, to attractions, repulsions, and their resultants. It is shown mathematically that, taking any two level or equipotential surfaces (see equipotential) which a particle might traverse in its motion, the difference of the squares of its velocities as it passed through them would be the same no matter from what point of space it started, nor what might be the direction and velocity of its initial motion. Thus, the square of the velocity at any instant could be deduced from that at any other by simply adding or subtracting a quantity dependent merely on the positions at these instants. In like manner, if a number of particles were moving about, subject to mutual attractions and repulsions, it is shown in dynamics that if to the sum of the masses, each multiplied by the square of its velocity, be added a certain quantity dependent only on the positions of the particles at that instant, this last sum would remain constant throughout the motion. Of these quantities, half the mass of a particle into the square of its velocity is termed its actual energy, or energy of motion— that is, its kinetic activity; while the quantity to be added to the sum of the actual energy in order to obtain a constant sum is termed the potential energy— that is, the latent or slumbering activity, or energy of position; the constant sum being termed the total energy. The corresponding general principle of physics is that the total energy of the physical universe is constant; this is the principle of the persistence or conservation of energy. (See below.) Examples of actual energy are the energy of sensible motion as in a moving cannon-ball, of sound-waves, of heat; of potential energy, the energy of position of a weight raised above the earth, of elasticity as in a bent bow, of electricity, chemical combination, etc. Potential or positional energy and actual or kinetic energy are in incessant interconversion; for positional energy implies force, or a tendency to motion, as much as kinetic energy implies motion or change of position. Thus, in the case of a swinging pendulum, the actual energy is null at the turning-points at the extremities of the swing, while the potential energy is at its minimum when the center of gravity is lowest; and the oscillation, but for resistances (as friction), would continue forever. Another equivalent version of the law of energy is as follows: Suppose a system of bodies were moving under the influence of those positional forces to which the law exclusively applies, and suppose that at any one instant all the particles were to strike squarely against elastic surfaces so as to have the directions of their motions reversed, but their velocities otherwise unaltered; then the whole series of motions would be performed backward, so that the particles would again pass through the same positions they had already passed through, and in the same intervals of time, but in the reverse order. Thus, a squarely rebounding cannonball in vacuo would move backward over the same trajectory, and with the same velocities, as in its forward motion, plunging into the mouth of the cannon again with exactly the velocity with which it had issued.
9. n. of water in motion, or in an elevated position;
10. n. of air in motion, as the wind;
11. n. the muscular energy of animals. To these might be added the energy of direct solar radiation, the energy of the tides, and some others of less importance. The source of all these forms of energy, except that of the tides, is to be found in the radiant energy of the sun.

Wiktionary

1. n. The impetus behind all motion and all activity.
2. n. The capacity to do work.
3. n. physics A quantity that denotes the ability to do work and is measured in a unit dimensioned in mass × distance²/time² (ML²/T²) or the equivalent.
4. n. An intangible, modifiable force (often characterized as either 'positive' or 'negative') believed to emanate from a person, place or thing and which is (or can be) preserved and transferred in human interactions; shared mood or group habit; a vibe, a feeling, an impression.

GNU Webster's 1913

1. n. Internal or inherent power; capacity of acting, operating, or producing an effect, whether exerted or not.
2. n. Power efficiently and forcibly exerted; vigorous or effectual operation.
3. n. Strength of expression; force of utterance; power to impress the mind and arouse the feelings; life; spirit; -- said of speech, language, words, style.
4. n. (Physics) Capacity for performing work.

WordNet 3.0

1. n. a healthy capacity for vigorous activity
2. n. any source of usable power
3. n. enterprising or ambitious drive
4. n. the federal department responsible for maintaining a national energy policy of the United States; created in 1977
5. n. forceful exertion
6. n. (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work; the units of energy are joules or ergs
7. n. an imaginative lively style (especially style of writing)