When a round object rolls along a straight line, a track on the round edge is called a roulette or a cycloid.

当一个圆沿着一条直线滚动时，圆边上一点的轨迹叫做旋轮线或摆线。

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When a round object rolls along a straight line, a track on the round edge is called a roulette or a cycloid.

当一个圆沿着一条直线滚动时，圆边上一点的轨迹叫做旋轮线或摆线。

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