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Centroid（形心）% }# x, C3 X; S+ x n
In geometry, the centroid or barycenter of an object X in n-dimensional space is the intersection of all hyperplanes that divide X into two parts of equal moment about the hyperplane. Informally, it is the "average" of all points of X.6 x0 [5 U2 g* ~
4 K3 R$ \+ L uThe geometric centroid of a physical object coincides with its center of mass if the object has uniform density, or if the object's shape and density have a symmetry which fully determines the centroid. These conditions are sufficient but not necessary.
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7 \' g. [4 d& y/ l0 L" G. ?The centroid of a finite set of points can be computed as the arithmetic mean of each coordinate of the points.
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) G; z1 M& I: j* p# GIn geography, the centroid of a region of the Earth's surface is often known as its geographic center.( ^0 a3 n/ ^1 v
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Neutral axis（中性轴）0 E, Q$ U6 H" `1 ~
An axis in the cross section of a beam, shaft or the like along which there are no longitudinal stresses / strains. If the section is symmetric (in both geometry and materials) the neutral axis is at the geometric centroid.3 X0 g' a* I0 m1 H) s6 l% R. B3 y
这个也许能有些帮助。 | 
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