Pilots from different countries understand body signals if they have the correct training. When you wave your arms up and down in a straight line, it means "yes".

如果接受了正确的训练，来自不同国家的飞行员都能理解身体信号。当你沿一条直线上下摆动手臂时，就表示“是”。

youdao

Your body should form a straight line from ankles to head [a].

你的身体从脚踝到头部应形成一条直线。

youdao

Keeping your elbow under your shoulder, push yourself up until your body is in a straight line.

以肘部力量支撑肩部，身体向上用力，使身体形成一条直线。

youdao

One way to say it is, every body will continue to remain in a state of rest or uniform motion in a straight line.

另外一种说法是,任何物体都会继续保持静止,或匀速直线运动的状态

耶鲁公开课 - 基础物理课程节选