自生的由自己落下或偶尔落下种子而长成的。用于种植物或庄稼 Growing from self-sown or accidentally dropped seed. Used of a cultivated plant or crop.
力偶具有相等磁性的两个力，平衡作用但反向，能导致旋转但不能造成平移 A pair of forces of equal magnitude acting in parallel but opposite directions, capable of causing rotation but not translation.
