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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Moment (physics) ： ウィキペディア英語版 Moment (physics) In physics, moment is a combination of a physical quantity and a distance. Moments are usually defined with respect to a fixed reference point or axis; they deal with physical quantities as measured at some distance from that reference point or axis. For example, a moment of force is the product of a force and its distance from an axis, which causes rotation about that axis. In principle, any physical quantity can be combined with a distance to produce a moment; commonly used quantities include forces, masses, and electric charge distributions. == Elaboration == In its most simple and basic form, a moment is the product of the distance to some point, raised to some power, multiplied by some physical quantity such as the force, charge, etc. at that point: : $\backslash mu\_n\; =\; r^n\backslash ,Q$, where $Q$ is the physical quantity such as a force applied at a point, or a point charge, or a point mass, etc. If the quantity is not concentrated solely at a single point, the moment is the integral of that quantity's density over space: : $\backslash mu\_n=\backslash int\; r^n\backslash ,\backslash rho(r)\backslash ,dr$ where $\backslash rho$ is the distribution of the density of charge, mass, or whatever quantity is being considered. More complex forms take into account the angular relationships between the distance and the physical quantity, but the above equations capture the essential feature of a moment, namely the existence of an underlying $r^n\backslash ,\backslash rho(r)$ or equivalent term. This implies that there are multiple moments (one for each value of ''n'') and that the moment generally depends on the reference point from which the distance $r$ is measured, although for certain moments (technically, the lowest non-zero moment) this dependence vanishes and the moment becomes independent of the reference point. Each value of ''n'' corresponds to a different moment: the 1st moment corresponds to ''n=1''; the 2nd moment to ''n=2'', etc. The 0th moment (''n=0'') is sometimes called the ''monopole moment''; the 1st moment (''n=1'') is sometimes called the ''dipole moment'', and the 2nd moment (''n=2'') is sometimes called the ''quadrupole moment'', especially in the context of electric charge distributions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Moment (physics)」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.