提出问题如图1所示,ab、ac、ad是竖直平面内三根固定的光滑细杆,a、b、c、d 四点位于同一圆周上,ad 处于圆的竖直直径.每根杆上各套着一个小滑环(可视为质点),三个滑环分别从b、c、d三处由静止释放运动到口(或从口由静止释放分别运动到 b、c、d 三处)所用时间分别为t_1、t_2、t_3,它们的大小关系是____. As shown in Figure 1, ab, ac, and ad are three fixed smooth thin rods in the vertical plane. The four points a, b, c, and d are on the same circumference, and ad is in the vertical diameter of the circle. Each rod Each set of a small slip ring (can be regarded as a particle), the three slip rings from the b, c, d from the static release of the three movements to the mouth (or from the mouth from the static release to move to b, c, d three The time used is t_1, t_2, and t_3, respectively, and their size relationship is ____.