矢量有，长度也有方向，因此通常，用箭头来表示。
A vector has a length and a vector has a direction and that's why we actually represent it by an arrow.
值得注意的是，具有轨道角动量的光，偏振方向(用箭头方向表示)在截面内部发生变化。
Note that in light with orbital angular momentum, the direction of polarization (denoted by the direction of the arrow) does not change across the cross section.
上图用红色箭头表示震中附近地面移动的相对方向和大小。
The image above USES red arrows to represent the relative direction and magnitude of the ground movement in the vicinity of the quake.
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