Talk:Doppler effect
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[edit] Sign Conventions
Is there any particular reason that the sign conventions are switched between the General and Analysis sections? Ehinson56 21:37, 3 January 2007 (UTC)
Perhaps I am being pedantic here but I have noted that there seems to be some inconsistence in the article as to referencing v as speed and velocity. As it is scalar, should this not really be referred to speed? I realize this is a minor concern. Agaudin 22:23, 7 November 2006 (UTC)
- I don't think so. My physics textbook has a similar treatment and uses the term "velocity". Since v is signed, it can't be treated as speed (magnitude of velocity). The direction isn't unspecified; it's assumed to be along a line joining the source and observer. Pfalstad 00:24, 13 November 2006 (UTC)
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Is the consensus still for placing the description of the relativistic treatment in its own article or should it be pulled back here? By the way, sorry for omitting the minor change flag on some of my recent updates. -- Alan Peakall 18:42 Dec 6, 2002 (UTC)
[edit] Doppler did not test his hypothesis (?)
According to Alec Eden: The Search for Christian Doppler. Springer Verlag 1992. Doppler didn't test his hypothesis, neither did he base it on observations. However, I am not quite comfortable with writing english, so I would not like to make alterations in the article totally on my own. Could anyone be ready to correct my grammar and spelliong?
- Well, according to "Asimov's Biographical Encyclopedia of Science and Technology" (1972 edition, Pan), Doppler is supposed to have spent two days in Holland with a flatbed carriage being pulled back and forth along a railway track, with trumpeters on the carriage playing various notes, and observers with perfect pitch by the track jotting down he actual notes that they heard. It could be a myth, of course, but it sounds like a rather elaborate thing to make up. Unfortunately, that book doesn't provide any further trackable references. ErkDemon 22:06, 30 October 2006 (UTC)
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- At this time (February 1845) Doppler lived in Prague with his family. The source above states that it was Christoph Hendrik Diederik Buys Ballot that performed the experiment. --Ekko 11:13, 8 November 2006 (UTC)
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- Okey-doke. Asimov's "biog" encyclopedia is rather lacking in detail, so your (more specific) book sounds like the more reliable source. ErkDemon 11:38, 16 January 2007 (UTC)
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[edit] not sure one of the formulas is correct
A similar analysis for a moving observer and a stationary source yields the observed frequency...
am I wrong, or does this formula seem incorrect... it would seem if one's speed equals the speed of the wave through the medium, the perceived wavelength should be infinite, and frequency should be zero. This is not what the equation suggests.
- It's okay, the quoted velocities are recession velocities. In the "moving-observer" formula, 1- (v0/v) can be rewritten to be more consistent with the format of the previous equation, as (v-v0) /v, which makes it more obvious that when v0=v (moving observer receding from a stationary source at the speed of sound), the predicted frequency does indeed drop to zero. Unfortunately textbook writers seem to quote the various Doppler equations and variants directly from previous books (probably to avoid awful typos), so the formats used can be rather inconsistent and seem to be based more on tradition than mathematical efficiency or consistency. Sometimes the usage of terms in the equations isn't compatible with the accompanying text, so sometimes even the "pros" can end up messing these things up. ErkDemon 22:30, 30 October 2006 (UTC)
[edit] Time Dependance?
I just learned about the doppler effect in my high school physics class, but it seems to me that if the source or observer are not colinear in their motion (they never pass through each other) then the percieved frequency would be related to the cosine of the angle between the motion and the line between the observer and the source. Specifically could the percieved frequency by something like: fa=(c-v*cos(A))fo/c where fa is the apparent frequency, c is the speed in a medium, A is the angle, and fo is the original frequency Also, couldnt you express the cos(A) between the direction of the motion and the line between the observer and the source as: x/(y^2+x^2)^1/2 since the cosine is adjacent (the "x" var) over the hypotenuse. Lastly, x, which is the distance along the line of motion, will be determined by time and velocity Soooo it seems that:
fa=[c-v*(v*t)/[y^2+(v*t)^2]^1/2]fo/c
for a stationary observer displaced by "y" from the net motion at time t (unfortunately i can't quite think of what t(0) would be)
[edit] doppler effect /red shift
I notice that there is a comment about red shift not being a result of doppler effect. I am not sure that is true, and it does seem to be in some dispute, especially considering the wikipedia article lists it specifically as a doppler effect measurement. Even if it is true that there is a subtle difference in that implementation, that is information that belongs on the red shift page and/or discussion. I do not think it belongs in this article. If there are no objections, I will remove that paragraph.
- Yes, remove it. I think the sentence is accurate but misleading. According to the redshift article, there are several sources of redshift, not just the doppler effect. Pfalstad 20:57, 30 June 2006 (UTC)
[edit] "A stationary microphone records moving police sirens at different pitches depending on their relative direction".
I found this a little confusing at first, as both cars have the same general direction. Would be clearer thus: "A stationary microphone records moving police sirens at different pitches depending on the direction of travel, relative to the microphone at any instant" MalFarrelle 11:07, 21 September 2006 (UTC)
[edit] More info...
Hi! Im doing a reasearch on the doppler effect in school... Does anyone know if there is some more info out there.. the only thing i seem to find is java applets demonstrating the doppler effect :( —The preceding unsigned comment was added by 85.225.22.158 (talk) 13:08, 21 March 2007 (UTC).
