你一定有这样的经验,当你站在马路旁边,即使没有去注视路面上车辆的行驶情况,单凭耳朵的听觉判断,就能感到一辆汽车正在驶过来,或者离你而去。这里面当然依靠汽车行驶的声音是渐强还是渐弱,但细细想想,主要还是根据汽车行驶的车轮声或剌叭声调的变化。原来,车辆驶近时,声音要变尖,也就是说,音调要高些;开过以后,远离的时候,音调会越来越低。为什么会这样呢?原来,声音 You must have the experience that when you stand by the side of the road, you can feel a car approaching or leaving you alone, without looking at the traffic on the road. Of course, the sound inside the car depends on whether it is getting stronger or getting fainter. However, if you think about it carefully, it mainly depends on the changes of the wheel sound or the beep tone of the car. It turned out that when the vehicle approached, the sound should be sharp, that is, the tone is higher; after the opening, when away, the pitch will be lower and lower. Why is it so? The original, voice