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斜面是一种简单机械,初中物理第一册中指出:用斜面提升重物,“使物体升高相同的高度,斜面越长越省力”。高中物理中斜面问题除在习题中出现以外,不再有专门的章节去讨论斜面。因此初中课本的上述结论,被视为简单的常识性问题,很少有人去怀疑它的正确性。笔者认为,这一结论只对理想的光滑斜面成立,对于实际中存在摩擦的斜面,并不完全正确,甚至可以说是错误的。
The slope is a simple machine. In the first book of junior high school physics, it is pointed out that lifting heavy objects with slopes “makes the objects rise at the same height, and the longer the slope, the more effort it takes”. The slope problem in high school physics is no longer a special chapter to discuss the slope except for the appearance in the exercises. Therefore, the above conclusions of junior high school textbooks are regarded as simple common sense issues. Few people doubt their correctness. The author believes that this conclusion is only valid for the ideal smooth slope, and it is not completely correct or even wrong for the actual friction slope.