每当下雨的时候,我们都会带上雨具上学．不知你是否注意,当穿着雨衣骑车时,雨会在雨衣帽的前檐形成水柱．如果你骑得较慢,水柱不会流到脸上,如图1．如果你骑得较快,外面的雨会把脸打湿,但水柱依然不会流到脸上．这是为什么呢？有一天下雨时,我做了一个实验．我撑着雨伞在雨中慢步走,观察到雨在伞边形成了水柱,但水柱没有落到我的身上,如图2．当我跑的时候,外面的雨把我的衣服打湿了,可是从伞的 Whenever it rains, we will bring rain gear to school. I do not know whether you pay attention, when riding a raincoat, the rain will form a water column in the front of the raincoat. If you ride slowly, the water column will not flow to your face, as shown in Figure 1. If you ride faster, the outside rain will wet your face, but the water column will not flow to your face. Why is this? One day when it rained, I did an experiment. I took an umbrella and walked slowly in the rain. I observed that the rain formed a water column on the edge of the umbrella, but the water column did not fall on me, as shown in Figure 2. When I was running, the rain outside wetted my clothes, but from the umbrella