consider this: in one frame of reference, there is an observer with a source of sound of some constant frequency and in another frame, there is another person, who can hear the sound produced by the source the first person has. when one is moving relative to another, weird things should begin to happen. this second guy can say he is stationary and that only the person with the source of sound is moving calculated the frequency of the sound he receives as: n(V/V-Vs). where n= original frequency V= velocity of sound Vs= velocity of source as observed by the person now, as it is impossible to say who is actually moving since there is no fixed reference, and since the person with the source of sound can argue he is stationary and the other person is moving, he calculates the frequency the other person should receive as n(V+Vo/V) where, n= original frequency V= velocity of sound Vo (=Vs) = velocity of the observer as observed by the first person. but both the equations give different answers! how can that be possible? consider this also: in one frame, there is a person with two like charges fixed with respect to him and in another frame, there is another person who can observe this first person and the charges. now, suppose the two frames are in motion relative to each other. now, the two people observe the electric field. and, since only the second person is in motion relative to the charges, only he must observe the magnetic field. this is when weird stuff starts again. suppose, now, that they are in relative motion and the two observers have made their observations, if the two charges are set free to move under the influence of whatever force there is that exists between them, the observations made by the two people should differ significantly because the charges should move only under coulumbian repulsion according to one and under both electrostatic and magnetic forces according to another. however, for these two charges, there can be just one definitive motion. hoe is that possible? tell me if i made any mistake somewhere and please correct me if m wrong. otherwise, please tell me how physics resolves this confusion. thank you.
Dear rohIT - things may sort out after studying material here: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html
Is the air stationary in both reference frames? is the speed of sound the same in both reference frames? (hint: the answer is "no" for both questions) Notice that there is a big difference with the case of the speed of light, since air is the medium of sound waves, but for light there is no medium.
RohlIT, your error in the first part is that you reversed the direction of motion or rather switched frames improperly, for an equation set up to work in one specific frame.
@ Q-reeus i know what doppler effect is...i am asking why it isnt symmetrical. Please Register or Log in to view the hidden image! as in why the observed frequency is different when (we assume) the observer moves from when (we assume) the source moves because there is no way we can say which one is actually moving.. @1100f assume that the answer for both your questions is yes and tell me why. @Russ_Watters i think reversing the direction is appropriate because both observe the other moving towards them in this question. and i dont get you when u say i switched the frames improperly. please elaborate Please Register or Log in to view the hidden image! and, please somebody answer the second question too Please Register or Log in to view the hidden image! thanks.
As per both #3 and #4, your conceptual error is in not allowing that acoustical Doppler is a preferred frame effect, unlike the SR relativistic Doppler. Also, your equations in #1 are not quite right. That material in HyperPhysics site I gave should have helped in this - did you study it? Well anyway here is another, that maybe easier to follow: http://physics.about.com/od/wavessound/a/dopplereffect.htm Note both the numerator and denominator terms! Please Register or Log in to view the hidden image! A hint here - with some thought it becomes apparent that wavelength, not frequency, is the frame independent but directionally dependent variable in acoustic Doppler (we naturally assume SR effects are negligible). Unfortunately most sources discuss only the case where there is direct inline motion between source and receiver. While the reader can reasonably assume that is also your scenario in #1, we do have to guess and in the general case, relative motion of Vs is ambiguous without a full vector description. For instance, relative motion of magnitude |Vs| transverse to the radius vector joining source and receiver will have a very different result to the normally shown relation - but it is still relative motion of |Vs|! Hope this helps. PS - you edited since I started answering, so I only address your (new) part addressed to myself. Your second part in #1 is really a separate topic for SR discussion, and maybe think about posting it as separate topic.
i just went through both the references you suggested. n i still dont see whats wrong with my equations. frequency observed by the observer at rest when the source is moving towards him n(V/V-Vs) frequency observed by the moving observer (towards the source) when the source is stationary n(V+Vo/V) and, thanks for your advice for the second question.
The link provided shows you that the equations are constructed so that the two possible directions are "moving toward each other" and "moving away from each other". Since both know they are moving toward each other, both would pick the same equation. That's not what the link says. Key word in both sentences being "towards" makes it clear that both cases should be choosing the first equation.
Sorry - in #6 I had confused your Vs (relative speed) with your V (sound speed) - since edited. Second thing here is that the expression fL = [(V + VL)/(V + Vs)]fs - (1) (notation slightly modified) shown in that article linked in #6 is appropriate to values determined entirely in the medium rest frame. If you wish to make the calculations in the source rest frame - when both receiver and medium are moving wrt source (your second case in #1), one approach is by first determining the frame invariant wavelength (appropriate here for inline motion only): lambda' = lambda = V/fL = V/[(V + Vs)/(V + VL)fs] - (2) (where primed quantities are those calculated in rest frame of source) and then computing fL' = |VL'|/lambda' (VL' = -Vs) [Oops, sorry but above expression should read |Vr'|/lambda', where Vr' = V'- VL', and VL' = -Vs as before. Vr' is the relative velocity between receiver and inline sound speed V', both as determined in source frame.] You should find this yields the right result. Another approach is to start from V', the speed of sound in the source rest frame, is V' = V-Vs (inline relative motion only, Vs and V the same sign). Then make the appropriate substitutions for other quantities in the modified version of (1) above.
rohIT - too much jumbling around in #10. Try instead: Under heading '2. Receiver moves, source is still' in article at http://physics-animations.com/Physics/English/dopp_txt.htm That is what I meant by invariant lambda, but my explanation/derivation not the best. Another source, that compares acoustic to SR Doppler: http://www.google.com.au/url?sa=t&r...0177phPJ_pAsESA&bvm=bv.42452523,d.aGc&cad=rja Finally, for a full vector based general expression, see: http://www.google.com.au/url?sa=t&r...7rcaAqCcwR4J95w&bvm=bv.42452523,d.aGc&cad=rja
