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覆杯实验是证明大气压存在的一个非常生动的实验:取一只玻璃杯注满水,用一张薄塑料片覆盖杯口,然后倒置,将看到塑料片不会掉下,水也不会流出。该实验的解释是:由于大气压的存在,其对塑料片施加一个向上的托力,该托力托住了塑料片和水柱。然而做该实验时笔者发现,其实在杯中注入半杯水实验也能成功。在平时教学中,教师很少会注意,但由此引起的一例研究性学习令笔者感触颇深。一次实验课后,有一位细心的学生发现做覆杯实验时杯中的水并未满,便邀请了几位学生一起来问,常规的回答当然是杯中气体的压强小于外界大气压,从而产生一个向上的压力差。本以为事情到此
Cup test is to prove the existence of atmospheric pressure is a very vivid experiment: Take a glass filled with water, with a thin plastic sheet covered cup mouth, and then inverted, will see the plastic sheet will not fall, the water will not Outflow. The explanation for this experiment is that due to the atmospheric pressure, it exerts an upward force on the plastic sheet, which holds the plastic sheet and the water column. However, when I did this experiment, I found that in fact, half a cup of water was injected into the cup and the experiment was successful. In normal teaching, teachers rarely pay attention, but the resulting case of research study so that I feel deeply. After an experiment, an attentive student found that the water in the cup was not full when she did the cup test. Several students were invited to ask. The conventional answer is of course that the pressure of the cup gas is less than the outside atmospheric pressure, resulting in An upward pressure difference. I thought this happened