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The instant centre of rotation, also called ''instantaneous velocity center'',〔''Illustrated Dictionary of Mechanical Engineering: English, German, French, Dutch, Russian'' (Springer Science & Business Media, 17 Apr. 2013 - 422 pages)〕 or also ''instantaneous centre'' or ''instant centre'', is the point fixed to a body undergoing planar movement that has zero velocity at a particular instant of time. At this instant, the velocity vectors of the trajectories of other points in the body generate a circular field around this point which is identical to what is generated by a pure rotation. Planar movement of a body is often described using a plane figure moving in a two-dimensional plane. The instant centre is the point in the moving plane around which all other points are rotating at a specific instant of time. The continuous movement of a plane has an instant centre for every value of the time parameter. This generates a curve called the moving centrode. The points in the fixed plane corresponding to these instant centres form the fixed centrode. == Pole of a planar displacement == The instant centre can be considered the limiting case of the pole of a planar displacement. The planar displacement of a body from position 1 to position 2 is defined by the combination of a planar rotation and planar translation. For any planar displacement there is a point in the moving body that is in the same place before and after the displacement. This point is the ''pole of the planar displacement'', and the displacement can be viewed as a rotation around this pole. Construction for the pole of a planar displacement: First, select two points A and B in the moving body and locate the corresponding points in the two positions; see the illustration. Construct the perpendicular bisectors to the two segments A1A2 and B1B2. The intersection P of these two bisectors is the pole of the planar displacement. Notice that A1 and A2 lie on a circle around P. This is true for the corresponding positions of every point in the body. If the two positions of a body are separated by an instant of time in a planar movement, then the pole of a displacement becomes the instant centre. In this case, the segments constructed between the instantaneous positions of the points A and B become the velocity vectors VA and VB. The lines perpendicular to these velocity vectors intersect in the instant centre. 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「instant centre of rotation」の詳細全文を読む スポンサード リンク
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