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Archive 1 |
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)
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)
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?
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.
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. So it seems that:
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)
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.
In my research on Satellite Geodesy, I have found that Doppler techniques have been used extensively as a method of satellite orbit determination. The basic concept being that satellites transmit on a stable frequency, so by measuring the frequency shift, one could derive velocity changes and other orbital parameters. One book that I have found that has a lot of information about this technique is:
A limited preview of this book is available on Google Books (see page 181 if it does not take you there automatically) here. I thought that this reference might provide some useful information on this topic as it relates to astronomy and geodesy. ChrisTracy ( talk) 23:32, 9 December 2007 (UTC)
Would it make sense to ask for semi-proection of this page? It appears to be a popular target for vandalism. Retoo ( talk) 14:55, 2 March 2008 (UTC)
Does anyone else find the illustration near the lead/toc difficult to look at, or even look indirectly at? It may be just that I am tired, but it seemed to spark quite a lot of lateral inhibition which can, of course, be pretty cool if thats what you're looking for. Possibly though considering we are reading text beside it, Image:Velocity0 70c.jpg might be nicer on the eyes and would be able to illustrate the same information? Any thoughts? aliasd· U· T 19:36, 9 May 2008 (UTC)
I have reverted two edits that replaced "monotonic decrease" with "monotonic increase" of the observed frequency as the source moves along a given trajectory. If you think about it, the monotonic decrease is correct (monotonic increase would mean a higher frequency after the source has passed the observer, which is obviously false). Sure, as long as the source is approaching, the observed frequency is higher than the source frequency, but it is decreasing (unless the source is on a collision course with the observer). -- Blennow ( talk) 14:15, 7 November 2008 (UTC)
The doppler effect in a medium depends on the RELATIVE velocity of the source and the medium AT THE TIME OF EMISSION, and also the RADIAL velocity of the observer and the wavefront normal AT THE TIME OF ABSORPTION.
The doppler effect for light depends on the RADIAL (not relative) velocity of the source AT THE TIME OF EMISSION, and the RADIAL velocity of the observer AT THE TIME OF ABSORPTION.
(This is demonstrated by the annual variance of the doppler shift of the stars due to the earth's changing radial velocity.
(relative velocity = radial velocity + transverse velocity)
Due to propagation delays, the emitted frequency doesn't equal the absorbed frequency until some time AFTER the source has passed.
I found the two images on the Simple English Wikipedia in the article of the same name to be much easier to understand than for the instance the one on the top right of this article. The images I'm referring to are Doppler_effect_diagrammatic.svg [1] and Dopplerfrequenz.gif [2], both which are found on Wikimedia Commons. Doppler_effect_diagrammatic.png [3] may also be a good one. All three images can be found on Wikimedia Commons and are therefore, as far as I know (I'm new) allowed to be used on this article. I believe these images would make the effect clearer to people that are not very familiar with physics and thus may have a harder time understanding the text. Woodcutterty ( talk) 15:10, 28 November 2009 (UTC)
It turns out that thumbnailing animated GIFs is not fully supported ( Wikipedia:Extended image syntax#Type). Compare the two versions at the right. Users of Internet Explorer (IE8) may notice a background artifact in the thumbnail version. This artifact does not appear in Firefox. To avoid it I am going to use the non-thumbnail version in the article. The disadvantage is that a non-thumbnail image cannot be resized. Ceinturion ( talk) 16:17, 29 November 2009 (UTC)
This doesn't seem right, esp. the proximity fuze bit. Doppler is widely used in weather radar and I believe aircraft radar and air traffic control radar as it allows much better discrimination between moving / non moving objects.
It sounds as if the editor hasn't read/doesn't understand the Doppler effect article.I can see what they mean, but it's hard to understand in this form. It is not necessarily or only used to "measure the velocity". Its main feature is it can detect moving objects while ignoring objects that are stationary ie Trees and parked vehicles. Too much emphasis on the "Distance" aspect.
New text in BOLD, Removed text crossed out
Radar
"The Doppler effect is used in some applicationstypes of radar, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each reflected wave increases, decreasing the frequency. In some situations, If the radar beam is fired at the moving car as it approaches, in which case each successive reflected wave travels a lesser distance, increasing the frequency. In either situation, calculations from the Doppler effect based on the frequency/wavelength change accurately determine the cars' velocity.
Moreover, the proximity fuze, developed during World War II, relies upon Doppler radar[fact] to explode at the correct time, height, distance, etc.[citation needed]
Other applications are weather radar, air traffic control radar, terrain following radars for low-flying military aircraft ie. F-111, B1-B, in fact any application where it is helpful to detect moving objects, not just a raw reflection irrespective of relative motion, eg. A doppler radar will ignore immobile/slow ground reflections (mountains, buildings, slow vehicles), ensuring that this 'ground clutter' does not get mistaken for fast moving passenger aircraft.[citation needed]"
Do laser speed 'traps' use doppler effect at all.? Or just make several distance measurements, and then calculate distance travelled between measurements vs time to get speed? Doppler should stop them measuring a road-side tree at 100 Kph for example.
--
220.101.28.25 (
talk)
23:06, 5 December 2009 (UTC)
The article currently reads
and goes on with the non-relativistic equation (emphasis mine above). Does that really mean the equation is not accurate at Mach 2? Why? Either that's a mistake, or the article should clarify the matter. I don't know which one it is, that's why I'm not fixing it myself. -- Gutza T T+ 23:25, 27 February 2010 (UTC)
Hunter33, I reverted your edit, as the original was correct. [4] On the other hand, although correct, that section is confusing instead of lucid to many readers. Probably it would be better to remove the lines "The above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle (but still with a constant velocity), the observed frequency that is first heard is higher than the object's emitted frequency. Thereafter, there is a monotonic increase in the observed frequency as it gets closer to the observer, through equality when it is closest to the observer, and a continued monotonic decrease as it recedes from the observer." Actually I think that applies to the digression "A common misconception" as well. Ceinturion ( talk) 09:39, 10 May 2010 (UTC)
Two days ago 190.134.15.113 removed the image at the right because "Erroneous image concept. Only the spectral lines are shifted, not the colours of the continous background." However, the background represents the colour perception by human observers on earth. It is what we would see using a spectroscope. The background is not about colour perception by humans or aliens living at those distant galaxies. Therefore I restored the image. Ceinturion ( talk) 06:28, 24 March 2011 (UTC)
Wave speed equal to frequency times wavelength is a material property. The first figure, upper part, gives the false impression that wave speed depends on source speed. A better caption could be “Waves seen from a source moving at constant velocity near the wave speed.” ( HCPotter ( talk) 08:50, 27 November 2011 (UTC))
but I believe retaining it with the revised caption would give insight into the Doppler equation origin that the page otherwise lacks. ( HCPotter ( talk) 13:14, 4 December 2011 (UTC))
For light a Doppler effect is readily developed from Lorentz time dilatation. Relativistic Doppler effect It gives an expression dependent on the relative velocity component in the direction from observer to source in which direction the light wavelength is presumed to change. For photons with volume proportional to wavelength cubed, however, the photon size will change. For most physical systems in which the source and observer move relative to some reference object, the component transformations are generally not Lorentzian. ( HCPotter ( talk) 09:56, 11 December 2011 (UTC))
All the four animated pictures in the section "general" have a little blemish: The first ring is slightly more spaced than the following ones. Could this be adjusted?
Thanks. 160.85.33.84 ( talk) 10:02, 16 January 2012 (UTC)
Regd. Analysis section: Does not explicitly mention which case is analysed - I assumed "moving source, stationary observer".
It explains "So it is actually the wavelength which is affected". Ok.
However, in the other case, "moving observer, stationary source", I was confused by the phrase "similar analysis". Analysis may be similar but does the same explanation "actually the wavelength which is affected" hold? In this case, doesn't wavelength "actually" remain same and relative/perceived sound speed change, thus affecting perceived frequency?
The article states that the wavelength is altered. This is not true. It is the timing difference between pulses that reveals how fast an object is moving and in which direction. — Preceding unsigned comment added by 78.146.91.223 ( talk) 10:21, 3 June 2012 (UTC)
Shouldn't we remove the somewhat nonsensical paragraph "a common misconception"? It says: "Craig Bohren pointed out in 1991 that some physics textbooks erroneously state that the observed frequency increases as the object approaches an observer and then decreases only as the object passes the observer. ... Bohren proposed that this common misconception might occur because the intensity of the sound increases as an object approaches an observer and decreases once it passes and recedes from the observer and that this change in intensity is misperceived as a change in frequency." I have no access to Bohren's article, but if he really said so he was probably not serious. It is very unlikely that authors of physics books fail to understand the difference between frequency and intensity. The Doppler effect is not a difficult concept. More likely it was just sloppy language. Authors on any subject may accidentally (and incorrectly) replace "is increased" by "increases" out of fear for the passive voice. A correct statement would have been: "the observed frequency is increased as the object approaches an observer and then is decreased only as the object passes the observer". There is no common misconception among authors of physics books, it is just sloppy language. Any objections against removal? 1st version of paragraph (2008) Current version Ceinturion ( talk) 10:55, 12 September 2012 (UTC)
This came up at GLAMcamp in London, so here are the sound example from de-wiki. I'm not sure how and where to integrate them into the article, so I'll leave that up to User:Andrew Gray ;-)
Die Tonbeispiele geben die Tonhöhen, die ein ruhender Beobachter hört, wenn eine Signalquelle an ihm vorbeifliegt. Sie vernachlässigen den Effekt, dass die sich entfernende Quelle länger zu hören ist als die sich nähernde:
Erhöht sich die relative Geschwindigkeit, verschieben sich die Frequenzen:
-- Cirdan ( talk) 10:44, 16 September 2012 (UTC)
There's a really neat combination of the two formulas in the german WP, so I'm going to paste it here and see if anyone else thinks that it should be included:
is the velocity of the observer and that of the source. The operators on top are used when they are moving towards and the ones below when they're moving away from each other.
—Preceding
unsigned comment added by
Merctio (
talk •
contribs)
I also think we should use the formula you cited, modifying the sign of the general equation. — Preceding unsigned comment added by Rosalia 13 ( talk • contribs) 03:43, 4 January 2017 (UTC)
About : should not the following formula be better f=f'(v+-vr)/(v-+vs) ( 134.184.100.155 ( talk) 03:48, 9 June 2010 (UTC))
While the use the and symbols may be mathematically redundant, it does aid understanding. My default textbook for all things physics is Resnick, Halliday & Krane Physics, 4th ed vol 1, John Wiley & Sons 1992 that was given to me during my undergraduate degree. It uses the and symbols. I would argue that their inclusion aids clarity. Graeme.e.smith ( talk) 19:41, 10 April 2012 (UTC)
I think the current formula should be written as , because is the velocity of the wave so that both of and should be on the same line of , then, when two velocities have same direction, we want the difference of their speeds, when two velocities have different directions, we want the sum of their speeds. Jh17710 ( talk) 21:18, 16 January 2011 (UTC)
In the section "General" is its written:
the relationship between observed frequency f and emitted frequency f0 is given by:
- where
- is the velocity of waves in the medium;
- is the velocity of the receiver relative to the medium; positive if the receiver is moving towards the source;
- is the velocity of the source relative to the medium; positive if the source is moving away from the receiver.
If I assume that c is meant to be always positive (is that the case here?) and for example the receiver to be at rest and the sender moving in the direction of the receiver with I get:
which means the frequency gets lower, which is wrong. I think correct would be:
- is the velocity of the source relative to the medium; positive if the source is moving towards the receiver. Manuel Walter ( talk) 19 March 2012
Somebody fixed it today by changing the formula: , instead of the definition of . An advantage of this fix is that it is compatible with a definition in the same paragraph ( ), and formulas in the next paragraph. Ceinturion ( talk) 20:40, 21 March 2012 (UTC)
The signs in the text are inconsistent with the signs in the image legends. Before choosing, let's see which conventions are used in different physics books.
The single coordinate systems are theoretically more fundamental, the dual coordinate systems might be more convenient in some practical problems. Ceinturion ( talk) 01:40, 14 December 2012 (UTC)
Strange: the speed of some of the animated gifs in the article is browser dependent. In Google Chrome the red dot in the left animation moves to the right in 1 second, but it is slowed down to 3 seconds in Internet Explorer (IE9). In contrast, The speed of the animated gif at the right is browser independent. Why is that? Ceinturion ( talk) 00:32, 18 December 2012 (UTC)
Today and last month there were contradictory edits concerning Rayleigh's backwards music effect occuring "in front of" or "behind" the source. [5] [6] Actually it should be correlated to before and after: "Music emitted when the observer was in front of the source, will be heard backwards, when the source is behind the observer." To avoid the confusion, we would better not mention the location, just like Rayleigh did. Ceinturion ( talk) 22:03, 15 February 2013 (UTC)
Mention the sudden onset, then gradual decrease, of the sound (intensity, not frequency) of a passing airplane, is merely due to the front of an airplane being quieter than the rear, even when on the ground. https://groups.google.com/d/topic/sci.physics.acoustics/vWwNsCZ_gwk/discussion Jidanni ( talk) 21:16, 7 December 2013 (UTC)
The gif animation used to demonstrate the pitch change of a moving vehicle seemed wrong to me.
In the animation, the wave travel forth travels at a faster speed and the wave travel backward travels slower after the car starts moving, which is not true. Unless the wave travel through different medium with different density, the speed that wave travels remains the same. Qranger1980 ( talk) 02:59, 4 March 2014 (UTC)AA
As far as I can tell, this has nothing to do with the Doppler effect and does not belong as part of this article. To make things worse, this could be a very confusing, misleading, and unneccesary bit of info to throw at the casual reader. I believe that naming it "Inverse Doppler effect" is a case of confusing misnomenclature, and if those who named the effect had chosen a different name, it would not have ended up here.
Now, I haven't taken time yet to go through the original articles and fully understand this, and I'm not sure I have the interest to do so, so if someone who knows more about the subject wants to weigh in, please do. It seems to me the "inverse" effect is just an interesting phenomenom related to wave propagation in a nonlinear medium under just the right conditions. The name came from the fact that it has the opposite overall effect to the 'doppler effect' on frequency, but the effect itself is physically completly unrelated.
I understand the reason for merging. The original article was not likely to be complete on it's own. However, I think it detracts from this article (a relatively important one) and recommend the merge be undone. Argentum2f ( talk) 16:15, 18 July 2014 (UTC)
Mention of the inverse Doppler effect is appropriate to an article on the Doppler effect. But to a non-scientist, the section is rather opaque. What would an inverse effect "look" like? If the Doppler effect produces a higher tone (shortened waves) followed by a lower tone (lengthened waves), would the inverse produce the, well, inverse? Why and how? Under what circumstances? KC 11:50, 5 May 2016 (UTC) — Preceding unsigned comment added by Boydstra ( talk • contribs)
The several references to "sirens" seem confusing. A typical "American mechanical siren" changes pitch because the rotor speeds up and slows down within the body of the mechanism (now simulated by electronic means). While the Doppler effect is also present, the much larger change in generated pitch largely conceals it.
The "European warbling siren" alternates two pitches: this was originally accomplished with two separate "horns" with different pitches (and is also now simulated by electronic means). The Doppler effect is much more apparent with this type of siren.
Does anybody else think that further explanation is necessary in the caption to the first animation or in the section devoted to "Sirens"? Yankeecook2 ( talk) 13:30, 6 March 2015 (UTC)
radar f' = f * ...?
the relativistic version is different, thus probably quite wrong, or some naïve approximation only.
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There is an image on top of the page claiming the waves emerging from the body of a swan to illustrate the Doppler effect. However, I believe this is wrong. To start with, the swan is not a wave source. It is an object moving in a medium. The ripples shown are due to drag, or something. I think this is similar to Cherenkov_radiation but for massive objects in a fluid. Same thing happens froma motor boat speeding, and it becomes very clear when the boat moves faster than wave propagation in the water. -- Ravn ( talk) 06:38, 4 September 2017 (UTC)
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A silent edit war seems to be going on (since June 24, three weeks ago) about adding/removing an external link to the http://www.falstad.com/ripple website. It seems to be going on in other wikipedia articles ( diffraction, wave) as well. Please discuss the advantages/disadvantages here instead of continuing the war. I am not a participant in the edit war, but let me start with a few observations. The falstad website is a collection of about 70 nice interactive ripple tank simulations, and only one (or two) of them is about the Doppler effect. It is a nice simulation but I don't see what it adds to the four animations that are already in the wikipedia article. Furthermore, the Doppler effect simulation is hidden down in a long menu list of 70 items, which isn't evident to the wikipedia user. If the external link to falstad is to stay, it needs a comment about which item from the list should be selected. In this respect the falstad website has become less useful compared to a few years ago because it has removed the direct link to the Doppler simulation.
Another point is: the external links section contains several links that are not working properly or that are not very useful. It needs some cleaning up. Proposal:
Ceinturion ( talk) 11:32, 15 July 2018 (UTC)
Someone is trying to push Doppler Shift Compensation (DSC) in a family of bats (bats that have a narrowly defined range of frequencies over which they are maximally sensitive, which is termed the acoustic fovea) to the top of the list of applications of the doppler effect. ( diff) This is not helpful to the general wikipedia reader, sirens and astronomy should be at the top of the list. DSC is not an "application" (it is a compensation, and esoteric). By the way, robotics, which someone put on top of the list last year, is another item that should be moved down in the list. Ceinturion ( talk) 16:20, 7 April 2020 (UTC)
Anonymous user 2601:2C3:4201:D70:E15B:E727:6A15:56BD, you changed the equation : incorrectly into a sequence of two equations . Why? Do you know the use of the plus or minus sign, for example in Resnick & Halliday: (link)? Ceinturion ( talk) 18:31, 3 June 2020 (UTC)
What? No mention of the fact that the Doppler effect was noted with the sound of a passing train's whistle back in the 19th century?
216.152.18.132 ( talk) 08:12, 13 April 2021 (UTC)
The relativistic Doppler effect has a different formulation than the "ordinary" Doppler effect due to length differences between observer and originator <ref: Wikipedia - Relativistic Doppler Effect>. I believe this should mentioned under the "Astronomy" paragraph along with the correct formula. — Preceding unsigned comment added by DrClark3 ( talk • contribs) 20:31, 5 November 2021 (UTC)
This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
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)
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)
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?
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.
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. So it seems that:
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)
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.
In my research on Satellite Geodesy, I have found that Doppler techniques have been used extensively as a method of satellite orbit determination. The basic concept being that satellites transmit on a stable frequency, so by measuring the frequency shift, one could derive velocity changes and other orbital parameters. One book that I have found that has a lot of information about this technique is:
A limited preview of this book is available on Google Books (see page 181 if it does not take you there automatically) here. I thought that this reference might provide some useful information on this topic as it relates to astronomy and geodesy. ChrisTracy ( talk) 23:32, 9 December 2007 (UTC)
Would it make sense to ask for semi-proection of this page? It appears to be a popular target for vandalism. Retoo ( talk) 14:55, 2 March 2008 (UTC)
Does anyone else find the illustration near the lead/toc difficult to look at, or even look indirectly at? It may be just that I am tired, but it seemed to spark quite a lot of lateral inhibition which can, of course, be pretty cool if thats what you're looking for. Possibly though considering we are reading text beside it, Image:Velocity0 70c.jpg might be nicer on the eyes and would be able to illustrate the same information? Any thoughts? aliasd· U· T 19:36, 9 May 2008 (UTC)
I have reverted two edits that replaced "monotonic decrease" with "monotonic increase" of the observed frequency as the source moves along a given trajectory. If you think about it, the monotonic decrease is correct (monotonic increase would mean a higher frequency after the source has passed the observer, which is obviously false). Sure, as long as the source is approaching, the observed frequency is higher than the source frequency, but it is decreasing (unless the source is on a collision course with the observer). -- Blennow ( talk) 14:15, 7 November 2008 (UTC)
The doppler effect in a medium depends on the RELATIVE velocity of the source and the medium AT THE TIME OF EMISSION, and also the RADIAL velocity of the observer and the wavefront normal AT THE TIME OF ABSORPTION.
The doppler effect for light depends on the RADIAL (not relative) velocity of the source AT THE TIME OF EMISSION, and the RADIAL velocity of the observer AT THE TIME OF ABSORPTION.
(This is demonstrated by the annual variance of the doppler shift of the stars due to the earth's changing radial velocity.
(relative velocity = radial velocity + transverse velocity)
Due to propagation delays, the emitted frequency doesn't equal the absorbed frequency until some time AFTER the source has passed.
I found the two images on the Simple English Wikipedia in the article of the same name to be much easier to understand than for the instance the one on the top right of this article. The images I'm referring to are Doppler_effect_diagrammatic.svg [1] and Dopplerfrequenz.gif [2], both which are found on Wikimedia Commons. Doppler_effect_diagrammatic.png [3] may also be a good one. All three images can be found on Wikimedia Commons and are therefore, as far as I know (I'm new) allowed to be used on this article. I believe these images would make the effect clearer to people that are not very familiar with physics and thus may have a harder time understanding the text. Woodcutterty ( talk) 15:10, 28 November 2009 (UTC)
It turns out that thumbnailing animated GIFs is not fully supported ( Wikipedia:Extended image syntax#Type). Compare the two versions at the right. Users of Internet Explorer (IE8) may notice a background artifact in the thumbnail version. This artifact does not appear in Firefox. To avoid it I am going to use the non-thumbnail version in the article. The disadvantage is that a non-thumbnail image cannot be resized. Ceinturion ( talk) 16:17, 29 November 2009 (UTC)
This doesn't seem right, esp. the proximity fuze bit. Doppler is widely used in weather radar and I believe aircraft radar and air traffic control radar as it allows much better discrimination between moving / non moving objects.
It sounds as if the editor hasn't read/doesn't understand the Doppler effect article.I can see what they mean, but it's hard to understand in this form. It is not necessarily or only used to "measure the velocity". Its main feature is it can detect moving objects while ignoring objects that are stationary ie Trees and parked vehicles. Too much emphasis on the "Distance" aspect.
New text in BOLD, Removed text crossed out
Radar
"The Doppler effect is used in some applicationstypes of radar, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each reflected wave increases, decreasing the frequency. In some situations, If the radar beam is fired at the moving car as it approaches, in which case each successive reflected wave travels a lesser distance, increasing the frequency. In either situation, calculations from the Doppler effect based on the frequency/wavelength change accurately determine the cars' velocity.
Moreover, the proximity fuze, developed during World War II, relies upon Doppler radar[fact] to explode at the correct time, height, distance, etc.[citation needed]
Other applications are weather radar, air traffic control radar, terrain following radars for low-flying military aircraft ie. F-111, B1-B, in fact any application where it is helpful to detect moving objects, not just a raw reflection irrespective of relative motion, eg. A doppler radar will ignore immobile/slow ground reflections (mountains, buildings, slow vehicles), ensuring that this 'ground clutter' does not get mistaken for fast moving passenger aircraft.[citation needed]"
Do laser speed 'traps' use doppler effect at all.? Or just make several distance measurements, and then calculate distance travelled between measurements vs time to get speed? Doppler should stop them measuring a road-side tree at 100 Kph for example.
--
220.101.28.25 (
talk)
23:06, 5 December 2009 (UTC)
The article currently reads
and goes on with the non-relativistic equation (emphasis mine above). Does that really mean the equation is not accurate at Mach 2? Why? Either that's a mistake, or the article should clarify the matter. I don't know which one it is, that's why I'm not fixing it myself. -- Gutza T T+ 23:25, 27 February 2010 (UTC)
Hunter33, I reverted your edit, as the original was correct. [4] On the other hand, although correct, that section is confusing instead of lucid to many readers. Probably it would be better to remove the lines "The above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle (but still with a constant velocity), the observed frequency that is first heard is higher than the object's emitted frequency. Thereafter, there is a monotonic increase in the observed frequency as it gets closer to the observer, through equality when it is closest to the observer, and a continued monotonic decrease as it recedes from the observer." Actually I think that applies to the digression "A common misconception" as well. Ceinturion ( talk) 09:39, 10 May 2010 (UTC)
Two days ago 190.134.15.113 removed the image at the right because "Erroneous image concept. Only the spectral lines are shifted, not the colours of the continous background." However, the background represents the colour perception by human observers on earth. It is what we would see using a spectroscope. The background is not about colour perception by humans or aliens living at those distant galaxies. Therefore I restored the image. Ceinturion ( talk) 06:28, 24 March 2011 (UTC)
Wave speed equal to frequency times wavelength is a material property. The first figure, upper part, gives the false impression that wave speed depends on source speed. A better caption could be “Waves seen from a source moving at constant velocity near the wave speed.” ( HCPotter ( talk) 08:50, 27 November 2011 (UTC))
but I believe retaining it with the revised caption would give insight into the Doppler equation origin that the page otherwise lacks. ( HCPotter ( talk) 13:14, 4 December 2011 (UTC))
For light a Doppler effect is readily developed from Lorentz time dilatation. Relativistic Doppler effect It gives an expression dependent on the relative velocity component in the direction from observer to source in which direction the light wavelength is presumed to change. For photons with volume proportional to wavelength cubed, however, the photon size will change. For most physical systems in which the source and observer move relative to some reference object, the component transformations are generally not Lorentzian. ( HCPotter ( talk) 09:56, 11 December 2011 (UTC))
All the four animated pictures in the section "general" have a little blemish: The first ring is slightly more spaced than the following ones. Could this be adjusted?
Thanks. 160.85.33.84 ( talk) 10:02, 16 January 2012 (UTC)
Regd. Analysis section: Does not explicitly mention which case is analysed - I assumed "moving source, stationary observer".
It explains "So it is actually the wavelength which is affected". Ok.
However, in the other case, "moving observer, stationary source", I was confused by the phrase "similar analysis". Analysis may be similar but does the same explanation "actually the wavelength which is affected" hold? In this case, doesn't wavelength "actually" remain same and relative/perceived sound speed change, thus affecting perceived frequency?
The article states that the wavelength is altered. This is not true. It is the timing difference between pulses that reveals how fast an object is moving and in which direction. — Preceding unsigned comment added by 78.146.91.223 ( talk) 10:21, 3 June 2012 (UTC)
Shouldn't we remove the somewhat nonsensical paragraph "a common misconception"? It says: "Craig Bohren pointed out in 1991 that some physics textbooks erroneously state that the observed frequency increases as the object approaches an observer and then decreases only as the object passes the observer. ... Bohren proposed that this common misconception might occur because the intensity of the sound increases as an object approaches an observer and decreases once it passes and recedes from the observer and that this change in intensity is misperceived as a change in frequency." I have no access to Bohren's article, but if he really said so he was probably not serious. It is very unlikely that authors of physics books fail to understand the difference between frequency and intensity. The Doppler effect is not a difficult concept. More likely it was just sloppy language. Authors on any subject may accidentally (and incorrectly) replace "is increased" by "increases" out of fear for the passive voice. A correct statement would have been: "the observed frequency is increased as the object approaches an observer and then is decreased only as the object passes the observer". There is no common misconception among authors of physics books, it is just sloppy language. Any objections against removal? 1st version of paragraph (2008) Current version Ceinturion ( talk) 10:55, 12 September 2012 (UTC)
This came up at GLAMcamp in London, so here are the sound example from de-wiki. I'm not sure how and where to integrate them into the article, so I'll leave that up to User:Andrew Gray ;-)
Die Tonbeispiele geben die Tonhöhen, die ein ruhender Beobachter hört, wenn eine Signalquelle an ihm vorbeifliegt. Sie vernachlässigen den Effekt, dass die sich entfernende Quelle länger zu hören ist als die sich nähernde:
Erhöht sich die relative Geschwindigkeit, verschieben sich die Frequenzen:
-- Cirdan ( talk) 10:44, 16 September 2012 (UTC)
There's a really neat combination of the two formulas in the german WP, so I'm going to paste it here and see if anyone else thinks that it should be included:
is the velocity of the observer and that of the source. The operators on top are used when they are moving towards and the ones below when they're moving away from each other.
—Preceding
unsigned comment added by
Merctio (
talk •
contribs)
I also think we should use the formula you cited, modifying the sign of the general equation. — Preceding unsigned comment added by Rosalia 13 ( talk • contribs) 03:43, 4 January 2017 (UTC)
About : should not the following formula be better f=f'(v+-vr)/(v-+vs) ( 134.184.100.155 ( talk) 03:48, 9 June 2010 (UTC))
While the use the and symbols may be mathematically redundant, it does aid understanding. My default textbook for all things physics is Resnick, Halliday & Krane Physics, 4th ed vol 1, John Wiley & Sons 1992 that was given to me during my undergraduate degree. It uses the and symbols. I would argue that their inclusion aids clarity. Graeme.e.smith ( talk) 19:41, 10 April 2012 (UTC)
I think the current formula should be written as , because is the velocity of the wave so that both of and should be on the same line of , then, when two velocities have same direction, we want the difference of their speeds, when two velocities have different directions, we want the sum of their speeds. Jh17710 ( talk) 21:18, 16 January 2011 (UTC)
In the section "General" is its written:
the relationship between observed frequency f and emitted frequency f0 is given by:
- where
- is the velocity of waves in the medium;
- is the velocity of the receiver relative to the medium; positive if the receiver is moving towards the source;
- is the velocity of the source relative to the medium; positive if the source is moving away from the receiver.
If I assume that c is meant to be always positive (is that the case here?) and for example the receiver to be at rest and the sender moving in the direction of the receiver with I get:
which means the frequency gets lower, which is wrong. I think correct would be:
- is the velocity of the source relative to the medium; positive if the source is moving towards the receiver. Manuel Walter ( talk) 19 March 2012
Somebody fixed it today by changing the formula: , instead of the definition of . An advantage of this fix is that it is compatible with a definition in the same paragraph ( ), and formulas in the next paragraph. Ceinturion ( talk) 20:40, 21 March 2012 (UTC)
The signs in the text are inconsistent with the signs in the image legends. Before choosing, let's see which conventions are used in different physics books.
The single coordinate systems are theoretically more fundamental, the dual coordinate systems might be more convenient in some practical problems. Ceinturion ( talk) 01:40, 14 December 2012 (UTC)
Strange: the speed of some of the animated gifs in the article is browser dependent. In Google Chrome the red dot in the left animation moves to the right in 1 second, but it is slowed down to 3 seconds in Internet Explorer (IE9). In contrast, The speed of the animated gif at the right is browser independent. Why is that? Ceinturion ( talk) 00:32, 18 December 2012 (UTC)
Today and last month there were contradictory edits concerning Rayleigh's backwards music effect occuring "in front of" or "behind" the source. [5] [6] Actually it should be correlated to before and after: "Music emitted when the observer was in front of the source, will be heard backwards, when the source is behind the observer." To avoid the confusion, we would better not mention the location, just like Rayleigh did. Ceinturion ( talk) 22:03, 15 February 2013 (UTC)
Mention the sudden onset, then gradual decrease, of the sound (intensity, not frequency) of a passing airplane, is merely due to the front of an airplane being quieter than the rear, even when on the ground. https://groups.google.com/d/topic/sci.physics.acoustics/vWwNsCZ_gwk/discussion Jidanni ( talk) 21:16, 7 December 2013 (UTC)
The gif animation used to demonstrate the pitch change of a moving vehicle seemed wrong to me.
In the animation, the wave travel forth travels at a faster speed and the wave travel backward travels slower after the car starts moving, which is not true. Unless the wave travel through different medium with different density, the speed that wave travels remains the same. Qranger1980 ( talk) 02:59, 4 March 2014 (UTC)AA
As far as I can tell, this has nothing to do with the Doppler effect and does not belong as part of this article. To make things worse, this could be a very confusing, misleading, and unneccesary bit of info to throw at the casual reader. I believe that naming it "Inverse Doppler effect" is a case of confusing misnomenclature, and if those who named the effect had chosen a different name, it would not have ended up here.
Now, I haven't taken time yet to go through the original articles and fully understand this, and I'm not sure I have the interest to do so, so if someone who knows more about the subject wants to weigh in, please do. It seems to me the "inverse" effect is just an interesting phenomenom related to wave propagation in a nonlinear medium under just the right conditions. The name came from the fact that it has the opposite overall effect to the 'doppler effect' on frequency, but the effect itself is physically completly unrelated.
I understand the reason for merging. The original article was not likely to be complete on it's own. However, I think it detracts from this article (a relatively important one) and recommend the merge be undone. Argentum2f ( talk) 16:15, 18 July 2014 (UTC)
Mention of the inverse Doppler effect is appropriate to an article on the Doppler effect. But to a non-scientist, the section is rather opaque. What would an inverse effect "look" like? If the Doppler effect produces a higher tone (shortened waves) followed by a lower tone (lengthened waves), would the inverse produce the, well, inverse? Why and how? Under what circumstances? KC 11:50, 5 May 2016 (UTC) — Preceding unsigned comment added by Boydstra ( talk • contribs)
The several references to "sirens" seem confusing. A typical "American mechanical siren" changes pitch because the rotor speeds up and slows down within the body of the mechanism (now simulated by electronic means). While the Doppler effect is also present, the much larger change in generated pitch largely conceals it.
The "European warbling siren" alternates two pitches: this was originally accomplished with two separate "horns" with different pitches (and is also now simulated by electronic means). The Doppler effect is much more apparent with this type of siren.
Does anybody else think that further explanation is necessary in the caption to the first animation or in the section devoted to "Sirens"? Yankeecook2 ( talk) 13:30, 6 March 2015 (UTC)
radar f' = f * ...?
the relativistic version is different, thus probably quite wrong, or some naïve approximation only.
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There is an image on top of the page claiming the waves emerging from the body of a swan to illustrate the Doppler effect. However, I believe this is wrong. To start with, the swan is not a wave source. It is an object moving in a medium. The ripples shown are due to drag, or something. I think this is similar to Cherenkov_radiation but for massive objects in a fluid. Same thing happens froma motor boat speeding, and it becomes very clear when the boat moves faster than wave propagation in the water. -- Ravn ( talk) 06:38, 4 September 2017 (UTC)
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A silent edit war seems to be going on (since June 24, three weeks ago) about adding/removing an external link to the http://www.falstad.com/ripple website. It seems to be going on in other wikipedia articles ( diffraction, wave) as well. Please discuss the advantages/disadvantages here instead of continuing the war. I am not a participant in the edit war, but let me start with a few observations. The falstad website is a collection of about 70 nice interactive ripple tank simulations, and only one (or two) of them is about the Doppler effect. It is a nice simulation but I don't see what it adds to the four animations that are already in the wikipedia article. Furthermore, the Doppler effect simulation is hidden down in a long menu list of 70 items, which isn't evident to the wikipedia user. If the external link to falstad is to stay, it needs a comment about which item from the list should be selected. In this respect the falstad website has become less useful compared to a few years ago because it has removed the direct link to the Doppler simulation.
Another point is: the external links section contains several links that are not working properly or that are not very useful. It needs some cleaning up. Proposal:
Ceinturion ( talk) 11:32, 15 July 2018 (UTC)
Someone is trying to push Doppler Shift Compensation (DSC) in a family of bats (bats that have a narrowly defined range of frequencies over which they are maximally sensitive, which is termed the acoustic fovea) to the top of the list of applications of the doppler effect. ( diff) This is not helpful to the general wikipedia reader, sirens and astronomy should be at the top of the list. DSC is not an "application" (it is a compensation, and esoteric). By the way, robotics, which someone put on top of the list last year, is another item that should be moved down in the list. Ceinturion ( talk) 16:20, 7 April 2020 (UTC)
Anonymous user 2601:2C3:4201:D70:E15B:E727:6A15:56BD, you changed the equation : incorrectly into a sequence of two equations . Why? Do you know the use of the plus or minus sign, for example in Resnick & Halliday: (link)? Ceinturion ( talk) 18:31, 3 June 2020 (UTC)
What? No mention of the fact that the Doppler effect was noted with the sound of a passing train's whistle back in the 19th century?
216.152.18.132 ( talk) 08:12, 13 April 2021 (UTC)
The relativistic Doppler effect has a different formulation than the "ordinary" Doppler effect due to length differences between observer and originator <ref: Wikipedia - Relativistic Doppler Effect>. I believe this should mentioned under the "Astronomy" paragraph along with the correct formula. — Preceding unsigned comment added by DrClark3 ( talk • contribs) 20:31, 5 November 2021 (UTC)