It is pointed out that translational kinetic energy and rotational kinetic energy mutually transferred by sliding friction force, but it only has positive acting.
讨论滑动摩擦力作功，说明了滑动摩擦力可以使刚体的平动动能和转动动能之间相互转换，但总是作负功。
The force which must be overcome to keep one surface moving over another in known as sliding friction.
而保证一个平面沿着另一个平面相对移动的力称为滑动摩擦力。
Scientists now believe that some of the force of friction is due to attraction between the molecules of one surface and those of the surface sliding over it.
现在科学家们认为有些摩擦力是由于物体表面的分子和另一物体表面游动的分子之间的吸引力所引起的。
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