When passengers are waiting for the subway on the platform, they must stand outside the 1-meter safety yellow line from the edge of the platform. Why is this safety line drawn? This safety line originates from a bizarre tragedy that occurred a century ago. On a winter day in 1905, at a small train station in Russia named Olodok, the stationmaster and 38 staff members lined up on both sides of the railway track to welcome the imperial envoy sent by Tsar Nicholas II for an inspection. Before long, the train rushed into the "human alley" formed by the 38 railway employees with a whistle. Those standing close to the train were just about to raise their bouquets to cheer when, suddenly, all the welcomers were pushed from behind and fell forward involuntarily... This "devilish push" left four people disabled for life, and the remaining 34 people, including the stationmaster, all became victims under the rolling wheels! After the tragedy, the local court began to investigate the truth of the incident. The locomotive was in good condition, and neither the driver nor the staff had operated illegally. After repeated investigations, the judge had no choice but to write the following sentence in the verdict: "Everyone is a lamb of God and will return to God's side sooner or later!" After learning about the verdict, Russian scientist Tsiolkovsky lamented, "What a pity that the judge didn't understand Bernoulli's principle..."
In fact, when a train is moving at high speed, the air around the train also flows forward. The closer the air is to the train, the faster it flows, almost reaching the same speed as the train. The stationmaster and his subordinates lined up in a close position to the train, forming two human walls. Between each human wall and the train, there was a narrow passage, with the air flowing rapidly behind the train. The pressure in front of the human wall was very low, while the air flowed much slower outside the human wall, and the pressure behind the human wall was relatively high. Thus, a pressure difference was formed between the front and back of the human wall. The closer people were to the train and the faster the train was moving, the greater the pressure difference would be, and people would inevitably fall forward. This is how the tragedy at Olodok Station occurred. To prevent such accidents from happening, people later set up a very conspicuous yellow safety line on the platform, which was designed according to the maximum speed of trains and subway trains entering the station. Standing outside this yellow line, people can safely wait for the train.