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maa105
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I was talking to one of my friends the other day about doppler effect and we went into the discussion of accelerating object and doppler effect. we both agreed that the frequency shift would vary in time. then we argued about the frequency shift for different observers and here is were it got interesting, after arguing for some time we took an example:
say there is a sound source emitting frequency f0=1kHz that starts accelerating from the origin from rest with acceleration a to the right at time t=0s. say also we have a observer at x=-1m, what I argued that at time 1/300s (time taken sound to travel from the sound source at origin to x=-1) the observer will start recording a frequency of f0 and then this frequency will start declining with time. similarly an observer at x=-2m will start recording frequency f0 at time 2/300s and that frequency will start declining with time. (see fig1 for illustration)
[URL]https://sites.google.com/site/javascriptevents/home/test.jpg[/URL]
Fig1
a consequence from the above image is that if say you take a specific point in time t=T where T>2/300s, at this specific time instance T each observer would register different frequency (see fig2). this too made sense since the signal received by observer one at t=T was emitted by the source at an earlier point in time than the one received by observer 2 at the same time t=T (due to propagation delay [the time it takes the signal to reach the observer] and due to the fact that the speed of sound is finite), which the speed of the source when it emitted the wave that was received at t=T by observer one is different than the speed of the source when it emitted the wave that was received at same time t=T by observer two. and due to this speed difference I reasoned that there should be a frequency shift between the two observers at time t=T (or any time instance for that matters)
[URL]https://sites.google.com/site/javascriptevents/home/test2.jpg[/URL]
Fig2
This reasoning made sense to me, but then my friend told me I was wrong and pulled of a pencil and paper and manipulated some equations to prove that both observers at x=-1 and x=-2 receive the same frequency at all points in time. his formulas made sense but then what is wrong in my previous reasoning?
[URL]https://sites.google.com/site/javascriptevents/home/test3.jpg[/URL]
Fig3 illustration of case study
say there is a sound source emitting frequency f0=1kHz that starts accelerating from the origin from rest with acceleration a to the right at time t=0s. say also we have a observer at x=-1m, what I argued that at time 1/300s (time taken sound to travel from the sound source at origin to x=-1) the observer will start recording a frequency of f0 and then this frequency will start declining with time. similarly an observer at x=-2m will start recording frequency f0 at time 2/300s and that frequency will start declining with time. (see fig1 for illustration)
[URL]https://sites.google.com/site/javascriptevents/home/test.jpg[/URL]
Fig1
a consequence from the above image is that if say you take a specific point in time t=T where T>2/300s, at this specific time instance T each observer would register different frequency (see fig2). this too made sense since the signal received by observer one at t=T was emitted by the source at an earlier point in time than the one received by observer 2 at the same time t=T (due to propagation delay [the time it takes the signal to reach the observer] and due to the fact that the speed of sound is finite), which the speed of the source when it emitted the wave that was received at t=T by observer one is different than the speed of the source when it emitted the wave that was received at same time t=T by observer two. and due to this speed difference I reasoned that there should be a frequency shift between the two observers at time t=T (or any time instance for that matters)
[URL]https://sites.google.com/site/javascriptevents/home/test2.jpg[/URL]
Fig2
This reasoning made sense to me, but then my friend told me I was wrong and pulled of a pencil and paper and manipulated some equations to prove that both observers at x=-1 and x=-2 receive the same frequency at all points in time. his formulas made sense but then what is wrong in my previous reasoning?
[URL]https://sites.google.com/site/javascriptevents/home/test3.jpg[/URL]
Fig3 illustration of case study
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