Frequency changes in respect to moving sources and observers

[Aphrael]

I am a little confused about the change in frequencies. I am working on a problem involving a train. The train is moving at a constant velocity and blows its horn at a certain frequency.

I know that the frequency heard by those on the train station will be f1= f/(1-(Vs/Vsound)) when the train is approaching the station where Vs is the constant spead of the train and Vsound is the speed of sound.

I also know that the frequency heard by those on the train station will be f1= f/(1+(Vs/Vsound)) when the train is receding from the station.

However, what is the sound heard by the people on the train. I thinking that as the passengers are moving at the same velocity as the train they would therefore hear the frequency the train was emitting. Is this correct and if not where am I going wrong in my thinking?

 

[ozymandias]

This is indeed correct.

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Assaf
http://www.physicallyincorrect.com/"

 

[ogb p]

As an expert in the field of sound and frequency, I can confirm that your understanding of the frequency changes in respect to moving sources and observers is correct. When the train is approaching the station, the frequency heard by those on the train station will be higher than the frequency emitted by the train due to the Doppler effect. This is because the sound waves are being compressed as the train moves towards the observer, resulting in a shorter wavelength and higher frequency. This can be calculated using the equation you mentioned, f1= f/(1-(Vs/Vsound)).

Similarly, when the train is receding from the station, the frequency heard by those on the train station will be lower than the frequency emitted by the train. This is because the sound waves are being stretched as the train moves away from the observer, resulting in a longer wavelength and lower frequency. This can be calculated using the equation f1= f/(1+(Vs/Vsound)).

As for the sound heard by the people on the train, you are correct in thinking that they would hear the frequency emitted by the train. This is because they are moving at the same velocity as the train, so the sound waves are not affected by the Doppler effect. The frequency they hear will be the same as the frequency emitted by the train, f.

I hope this clarifies any confusion you had about the change in frequencies. The Doppler effect is a well-studied phenomenon in physics and is crucial in understanding the behavior of sound waves in relation to moving sources and observers. Keep up the good work in your studies!