Why do the Doppler effect equations yield different frequencies?

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    Doppler Doppler effect
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Discussion Overview

The discussion revolves around the Doppler effect equations for sound, specifically addressing why different frequencies are obtained when considering relative motion between two cars and a stationary point. The scope includes theoretical exploration of the Doppler effect and its implications in classical motion scenarios.

Discussion Character

  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant questions why the Doppler effect equations yield different frequencies when using both raw and relative speeds of two cars moving towards or away from each other.
  • Another participant suggests that the speed of the source relative to the medium, as well as the observer, must be considered, implying that this affects the perceived frequency.
  • There is a discussion about whether classic motion scenarios would yield the same results as the Doppler effect, with some participants expressing confusion over the differences.
  • One participant emphasizes the importance of relative motion to the medium, particularly in scenarios where the source approaches the speed of sound.
  • Participants express difficulties accessing a cited resource intended to clarify the discussion, leading to further exchanges about the link's functionality.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons behind the differing frequencies produced by the Doppler effect equations. Multiple viewpoints regarding the importance of relative motion to the medium and the interpretation of the equations remain contested.

Contextual Notes

Some participants express uncertainty about the applicability of classic motion scenarios to the Doppler effect, indicating a potential limitation in understanding the underlying principles. Additionally, there are unresolved issues regarding the accessibility of external resources that may provide further clarification.

Zeteg
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In the doppler effect equation for sound, measuring frequency, I have the following question:

Car 1-20m/s--> Car 2-30m/s-->
--POINT A--


With the above "diagram", we have car 1 going at 20 m/s, right, and car two, 30m/s right, with respect to point A (doesn't have to be those values, just an example).

If we were to look at car 2, relative to car 1, car 2 would be moving away from car 1 at 10m/s. However, when we plug both the raw values, and the relative values into the equation, they yield a different frequency. Why is this? :|
 
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Zeteg said:
If we were to look at car 2, relative to car 1, car 2 would be moving away from car 1 at 10m/s. However, when we plug both the raw values, and the relative values into the equation, they yield a different frequency. Why is this? :|
I think you have to take into account the speed of the source relative to the medium as well as the observer. Have a look at this:
http://usna.edu/Users/physics/mungan/Scholarship/DopplerEffect.pdf

AM
 
Last edited by a moderator:
Yes, I'm aware of that. However, why would that be different? In classic motion scenarios, it renders the same answer, does it not? Since sound isn't in any special realms of physics, why is this different?
 
Well, you would be hearing a different sound while you are in Car 1 and while you are on the ground, would you not?
 
Zeteg said:
Yes, I'm aware of that. However, why would that be different? In classic motion scenarios, it renders the same answer, does it not? Since sound isn't in any special realms of physics, why is this different?
The cite I gave you should explain it for you. Think about the case in which the car is traveling at the speed of sound. Does the sound every reach an observer at rest with respect to the medium positioned behind the car? How about in front? So the motion relative to the medium is important.

AM
 
Andrew Mason said:
The cite I gave you should explain it for you. Think about the case in which the car is traveling at the speed of sound. Does the sound every reach an observer at rest with respect to the medium positioned behind the car? How about in front? So the motion relative to the medium is important.

AM

The site doesn't work =(
I understand your example, I'm still wondering why that is, though. I'll try and figure it out :D
 
Last edited:
I have that installed, and I can read pdfs :P The link simply does not work for me =\
 
Zeteg said:
I have that installed, and I can read pdfs :P The link simply does not work for me =\
You must be copying it and pasting it into your browser. That won't work. You have to click it

AM
 
  • #10
I am clicking it. I know how to operate a computer... ... =x
 

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