All extrapolation operators face the problem of choosing the reference velocity due to continuation in depth.

此类波场外推算子沿深度层进行波场外推，都存在参考速度选择问题。

youdao

So the Earth is an inertial frame of reference, if you go in a train relative to the Earth at constant velocity, you're also inertial.

所以,地球是一个惯性参考系,如果你坐在相对于地球匀速运动的火车里,你也处于惯性状态

耶鲁公开课 - 基础物理课程节选

Second formula tries to relate the final velocity of some time, t, to the initial velocity and the distance traveled with no reference to time.

第二个式子能把某段时间t的末速度,和初速度,经过的路程联系在一起,并且不引入时间

耶鲁公开课 - 基础物理课程节选