在乘火车或地铁的时候,你注意到没有,在靠近站台的边缘上都画有一条白线,它叫做安全线.当火车进出站时,乘务人员总是呼唤乘客站在安全线外,这是为什么呢?为解释这个现象,我们首先研究流体流速和压强之间的关系,在一根粗细不均匀的管子里,在粗和细部分各插一支压强计,让流管中充满液体.当流管中的液体没有流动时,两个压强 When you take the train or the subway, you notice that there is a white line on the edge near the platform. It is called the safety line. When the train enters or exits the station, the crew always calls the passengers to stand outside the safety line. Why? To explain this phenomenon, we first study the relationship between fluid velocity and pressure. In a tube of uneven thickness, insert a pressure gauge in each of the coarse and fine sections, and let the flow tube be filled with liquid. When the liquid in the flow tube does not flow, two pressures