a back-and-forth motion

• 来回移动

a back-and-forth motion的用法和样例：

例句

1. The shuttle moves backwards and forwards through the warp.
   梭子在经线中来回移动。
2. The conjuror made a few passes with his hand overthe hat.
   魔术师用手在帽子上方来回移动了几下。