磨损量与滑动摩擦功呈线性关系，与滑动距离成正比。
Mass loss is linear with sliding friction works and in proportion to sliding distances.
所以摩擦力做负功-，转化成热能。
理论上，一个无摩擦力的，或者说是理想的机器，输入和输出的功相等，因此效率是1，或者说是100%。
In a theoretically frictionless, or ideal, machine, the work input and work output are equal, and the efficiency would be 1, or 100%.
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。
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。
It is pointed out that translational kinetic energy and rotational kinetic energy mutually transferred by sliding friction force, but it only has positive acting.
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