当声源和观察者之间发生相对运动时 ,观察者听到的声波频率就会发生变化 ,这就是著名的多普勒效应 .多普勒效应是新版高中教材中新加的一节 .在这一节中 ,我们常常会遇到这样的一些说法或习题 :人站在路旁 ,听到迎面驶来火车的鸣笛声 ,声调会越来越高 ;火车驶去时 ,听到的声调 When the relative motion occurs between the sound source and the observer, the frequency of sound waves heard by the observer changes. This is known as the Doppler effect. The Doppler effect is a new section in the new high school textbooks. In this section, we often encounter such statements or exercises: People stand on the side of the road, hear the whistle of the oncoming train, the tone will be higher and higher, and when the train departs, the tone will be heard.