action

—actionless, adj.

/ak"sheuhn/, n.

1. the process or state of acting or of being active: The machine is not in action now.

2. something done or performed; act; deed.

3. an act that one consciously wills and that may be characterized by physical or mental activity: a crisis that demands action instead of debate; hoping for constructive action by the landlord.

4. actions, habitual or usual acts; conduct: He is responsible for his actions.

5. energetic activity: a man of action.

6. an exertion of power or force: the action of wind upon a ship's sails.

7. effect or influence: the action of morphine.

8. Physiol. a change in organs, tissues, or cells leading to performance of a function, as in muscular contraction.

9. way or manner of moving: the action of a machine or of a horse.

10. the mechanism by which something is operated, as that of a gun or a piano.

11. a military encounter or engagement; battle, skirmish, or the like.

12. actual engagement in fighting an enemy; military or naval combat: He saw action in Vietnam.

13. Literature. the main subject or story, as distinguished from an incidental episode.

14. Theater.

a. an event or series of events that form part of a dramatic plot: the action of a scene.

b. one of the three unities. Cf. unity (def. 8).

15. the gestures or deportment of an actor or speaker.

16. Fine Arts. the appearance of animation, movement, or emotion given to figures by their attitude, position, or expression.

17. Law.

a. a proceeding instituted by one party against another.

b. the right of bringing it.

18. Slang.

a. interesting or exciting activity, often of an illicit nature: He gave us some tips on where the action was.

b. gambling or the excitement of gambling: The casino usually offers plenty of action.

c. money bet in gambling, esp. illegally.

19. Eccles.

a. a religious ceremony, esp. a Eucharistic service.

b. the canon of the Mass.

c. those parts of a service of worship in which the congregation participates.

20. in action,

a. performing or taking part in a characteristic act: The school baseball team is in action tonight.

b. working; functioning: His rescuing the child was bravery in action.

21. out of action, removed from action, as by sudden disability: The star halfback is out of action with a bad knee.

22. piece of the action, Informal. a share of the proceeds or profits: Cut me in for a piece of the action.

23. take action,

a. to start doing something: As soon as we get his decision, we'll take action.

b. to start a legal procedure.

adj.

24. characterized by brisk or dynamic action: an action car; an action melodrama.

[1300-50; < L action- (s. of actio), equiv. to act(us) (ptp.; see ACT) + -ion- -ION; r. ME accioun < AF < L]

Syn. 1. movement, operation. 2. ACTION, ACT, DEED mean something done. ACTION applies esp. to the doing, ACT to the result of the doing. An ACTION usually lasts through some time and consists of more than one act: to take action on a petition. An ACT is single: an act of kindness. DEED emphasizes the finished or completed quality of an act; it may imply an act of some note, good or bad: an irrevocable deed; a deed of daring. 4. behavior. 12. brush, encounter, fight, skirmish. See battle. 15. plot.

Ant. 1. rest, inactivity.

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(as used in expressions)

Action Française

action painting

action potential

affirmative action

bolt action

class action

mass action law of

political action committee

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▪ physics

      in theoretical physics, an abstract quantity that describes the overall motion of a physical system. Motion, in physics, may be described from at least two points of view: the close-up view and the panoramic view. The close-up view involves an instant-by-instant charting of the behaviour of an object. The panoramic view, on the other hand, reveals not only a complete picture of the actual behaviour of an object but also all the possible routes of development connecting an initial situation with a final situation. From the panoramic view, each route between the two situations is characterized by a specific numerical quantity called its action. Action may be thought of as twice the average kinetic energy of the system multiplied by the time interval between the initial and final position under study or, again, as the average momentum of the system multiplied by the length of the path between the initial and final positions.

      The value of the action for any actual motion of a system between two configurations is always a minimum or a maximum. In most instances, the behaviour of the system follows the path of minimum, or least, action. In an optical system, such as a microscope, light travels along the path of least action as it undergoes bending in the lenses. For light, action is proportional to the time of travel, so that the light travels the path that takes the least time.

      With the beginning of quantum theory (1900), the concept of action took on a new importance. In describing the behaviour of molecular or atomic particles, one had to invoke a previously unsuspected restriction. Only those states of motion are possible in which actions are whole-number multiples of a certain very small number, known as Planck's constant, named for the German scientist Max Planck, who first proposed a discrete, or quantized, behaviour for objects of subatomic dimensions. Thus Planck's constant is the natural unit, or quantum, of action.

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