Just high; On the contrary, the tone sounds low. This phenomenon is called Doppler effect, which is based on the discoverer Christian Andreas Doppler.
Doppler, 1803- 1853), an Austrian physicist and mathematician, first discovered this effect in 1842.
To understand this phenomenon, it is necessary to investigate the propagation law of sound waves emitted by whistle when the train approaches at a uniform speed. As a result, the wavelength of sound waves becomes shorter, just like
The wave is compressed. Therefore, the number of waves propagating in a certain time interval increases, which is also the reason why the observer feels the pitch becomes higher. On the contrary,
As the train goes away, the wavelength of sound waves becomes larger, as if the waves are stretched. Therefore, the sound sounds very low. Quantitative analysis shows that f 1=(u+v0).
/(u-vs)f, where vs is the velocity of the wave source relative to the medium, v0 is the velocity of the observer relative to the medium, f is the natural frequency of the wave source, and u is the wave.
Propagation velocity in static medium. When the observer moves to the wave source, v0 takes the plus sign; When the observer is far away from the wave source (that is, along the wave source), v0 is negative.
No, when the wave source moves to the observer, vs is preceded by a negative sign; When the front wave source deviates from the observer's motion, Vs takes the plus sign. It is easy to know from the above formula that when the observer interacts with the sound source,
When approaching, f1> f; When the observer and the sound source are far apart. f 1