《初中物理教程》(书海出版社)第13页有如下一题:小明同学站在火车轨道旁,一列正在鸣笛的火车飞驰而过,则他听到的鸣笛声的频率将()在教学过程中,我发现不少教师有这样一种认识:在火车未到达小明之前,听到的鸣笛声的频率越来越高;当火车经过小明以后,听到的鸣笛声频率越来越低. The 13th page of the junior high school physics tutorial (Shuhai publishing house) has the following question: Xiaoming’s classmates are standing beside the train track, and the speed of the whistle sound he hears will be as he flies by a train whispering () During the teaching process, I discovered that many teachers have such an understanding: Before the train reaches Xiaoming, the frequency of the whistling sound heard is getting higher and higher; when the train passes Xiaoming, the frequency of the whistling sound heard The lower it comes.