科学家们认为这个速度加上行星的重量屈服于强大的重力牵引力，可以改变行星的运行轨道。
Scientists think that this speed coupled with the planet's heft yields strong gravitational tugs that can alter the planets orbit.
由于类似空气阻力的牵引作用，这些气体的（运行）速度减缓。
The gas was slowed by a drag force similar to air resistance.
在拖车运行时必须谨慎地操纵控制系统，否则牵引机就会被推倒。
Great care had to be taken with the control systems for a powered trailer because, when turning, it can push the tractor unit over.
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