Action (physics)

In physics, action is an attribute of the dynamics of a physical system. It is a mathematical functional which takes the trajectory, also called path or history, of the system as its argument and has a real number as its result. Generally, the action takes different values for different paths. Action has the dimensions of [energy]·[time] or [momentum]·[length], and its SI unit is joule-second. This is the same unit as that of angular momentum.

Introduction

Empirical laws are frequently expressed as differential equations, which describe how physical quantities such as position and momentum change continuously with time. Given the initial and boundary conditions for the situation, the "solution" to these empirical equations is an implicit function describing the behavior of the system.

There is an alternative approach to finding equations of motion. Classical mechanics postulates that the path actually followed by a physical system is that for which the action is minimized, or, more generally, is stationary. In other words, the action satisfies a variational principle: the principle of stationary action (see also below). The action is defined by an integral, and the classical equations of motion of a system can be derived by minimizing the value of that integral.

Action!

Action! may refer to:

See also

Action! (Desmond Dekker album)

Action! is an album by Jamaican rocksteady and ska group Desmond Dekker & the Aces that they released in 1968. Singer-songwriter Desmond Dekker composed all of the tracks, which includes the song "007 (Shanty Town)".

Track listing

All songs written by Desmond Dekker.

See also

References

Combat

Combat or fighting is a purposeful violent conflict meant to weaken, establish dominance over, or kill the opposition, or to drive the opposition away from a location where it is not wanted or needed.

The term combat (French for fight) typically refers to armed conflict between opposing military forces in warfare, whereas the more general term "fighting" can refer to any physical or verbal conflict between individuals or nations. Combat violence can be unilateral, whereas fighting implies at least a defensive reaction. A large-scale fight is known as a battle. A verbal fight is commonly known as an argument.

Background

Combat may take place under a specific set of rules or be unregulated. Examples of rules include the Geneva Conventions (covering the treatment of people in war), medieval chivalry, the Marquess of Queensberry rules (covering boxing) and several forms of combat sports.

Combat in warfare involves two or more opposing military organizations, usually fighting for nations at war (although guerrilla warfare and suppression of insurgencies can fall outside this definition). Warfare falls under the laws of war, which govern its purposes and conduct, and protect the rights of combatants and non-combatants.