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它未曾变过,如果没有空气阻力,或任何摩擦力。
That never changes if there is no air drag or air friction of any kind.
youdao
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滚动轴承的优点是它产生的摩擦力较小。
The advantage of rolling bearing is that they cause less friction.
youdao
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滚动轴承的优点是它产生的摩擦力较小。
The advantage of rolling bearing is that they cause less friction.
youdao