凡是去过火车站的人都应该有这样的经验 :当火车由远处开过来时 ,汽笛声的音调迅速变高 (实际上是频率增大 ) ,而当列车离你远去时 ,汽笛声的音调会变得低沉 (实际上是频率变低 )。同样 ,坐过火车的人也会发现 ,当旁边的复线上有列车开过来时 ,汽笛声急剧变尖 ,十分刺耳。在大? Anyone who has been to the station should have had the experience that when the train came in a distance, the siren’s sound quickly became higher (in fact the frequency increased) and when the train left you the whistle The tone will get low (actually the frequency goes down). Similarly, those who have taken the train will find that the whistle is sharp and sharp when the train on the second line next to it comes over. In the big?