最速降线

        本展品有三条轨道，一条是直线，一条是任意曲线，一条是摆线。虽然摆线的距离最长，但球从摆线滑下所用的时间最短，所以摆线又叫?#26368;速降线?#12290;

        物体沿轨道下降的速度不是简单得只取决于轨道的长度，而且还要取决于轨道的形状。这三个球下落是重力作用的结果，球所受重力沿轨道切线方向的分量越大，下落的速度就越快，而摆线轨迹是一条圆滚曲线，它的轨迹比较陡峭，重力在它切线方向上的分量比较大，球的下落速度比较快，先到达终点，而直线和另一条曲线的轨道虽然短，但球下落的速度较摆线上的球下落速度慢，因此后到达终点。
   

THE FASTEST FALLING LINE

        The exhibit has three tracks: one straight line, one arbitrary curve and one cycloid. Although the cycloid is the longest in distance, the ball falls the fastest along the cycloid. Therefore, it is called “the fastest falling line ” . 

        The speed an object falls along a track is not directly determined by length of the track. It also depends on the shape of the track. Falling of the three balls is the result of gravity .the greater the component of gravity along the tangent direction of the track, the faster the falling speed. Track of the cycloid is a cyclical curve and is steeper, thus the component of gravity along the tangent direction is bigger, and thus the ball falls faster and reaches the final point earlier. Although the tracks of the straight line and the other curve are shorter, they fall slower and reach the final point later.