当参考系相对于另一个惯性系做匀速直线运动时，它也可以视为惯性系。
When a reference frame moves at constant velocity in a straight line relative to another inertial frame, it can also be regarded as an inertial frame.
When a reference frame moves at constant velocity in a straight line relative to another inertial frame, it can also be regarded as an inertial frame.