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初中《物理》第一册p.182在讲到利用斜面能省力时,写道:“利用斜面,我们多通过了距离,但省丁力。山区的公路修得盘旋曲折,延长了爬坡的距离,就是为了省力。”课本给出了一幅盘山公路的照片,进而在练习题中出了道题:“骑自行车上坡,走S形路线省力。为什么?”似乎这两个例子都是为了说明只要延长爬坡距离,就能省力了。笔者认为第二例子放在这里是不合适的,尽管在日常生活中人们骑自行车上坡走S形路线确实感到比较省力,但其原因和盘山公路相比要复杂得多,下面就对这问题作一分析。盘山公路的路面宛延曲折,就是为了使
When the use of inclined planes saves energy, junior high school “Physics” Book One p.182 writes: “Using slopes, we have adopted more distances, but the provincial Dingli. The highways in the mountains have been hovering and twisting, extending the distance of climbing. It is to save the effort.” The textbook gives a picture of the Panshan Highway, and proceeds with the question in the exercises: “Biking uphill and taking the S-shaped route saves effort. Why?” It seems that both examples are for illustration As long as the climbing distance is extended, it will save people’s effort. The author believes that the second example is not appropriate here. Although people take the S-shaped route uphill in daily life, they actually feel more effort, but the reason is much more complicated than that of Panshan Highway. Here’s the problem. Make an analysis. The road on the Panshan Highway is prone to twists and turns.