Independence of speed of sound from motions of source and receptor
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From: Richard Dobson on 23 Mar 2010 21:13 On 24/03/2010 00:43, Bappa wrote: >> Except of course the "sources of sound" are not moving. > > Why of course? The sources of sound are of course moving, as the > sources of sound are the vibrating air columns forcefully pushed aside > by the lateral pressure of thermal expansion. > Not in the case of lightning. Don't confuse your incorrect analogy with the original thing being described. > > The very idea of a theoretical wave It's not "theoretical" - it is a physical phenomenon that can be observed. Obviously. ... > > As I have written earlier, from the reference given, Your reference says nothing to support your "theory"; indeed quite the opposite. Large or small, waves propagate through a medium - it really is as simple as that. the nature of > near thunder is first high frequency cracks, the main sound burst, > then a fading low frequency rumble, all in time sequence. Now, this > shows that the high frequency comes first, the mid frequency second, > and the low frequencies last? Why so? Rather than just guess wildly, learn from a more comprehensive reference: http://www.lightningsafety.com/nlsi_info/thunder2.html Whatever reasons you may have for trying to prove a variable speed of light (or whatever it is you ~are~ trying to prove), don't waste time using the speed of sound in air as an applicable analogy. It isn't. Richard Dobson
From: Richard Dobson on 24 Mar 2010 05:18 On 24/03/2010 01:39, Bappa wrote: > On Mar 24, 12:13 pm, Richard Dobson<richarddob...(a)blueyonder.co.uk> > wrote: >> On 24/03/2010 00:43, Bappa wrote: >> >>>> Except of course the "sources of sound" are not moving. >> >>> Why of course? The sources of sound are of course moving, as the >>> sources of sound are the vibrating air columns forcefully pushed aside >>> by the lateral pressure of thermal expansion. >> >> Not in the case of lightning. Don't confuse your incorrect analogy with >> the original thing being described. > > Why not? Lightning causes heat, expansion, and as a consequence, > rapid movement of air in all directions. it is the equivalent of the > earthquake that causes the tsunami. My analogy is valid, > mathematically, as shown earlier. > Nope, you were using the analogy of pianos or organ pipes flying off in all directions; that is the analogy that is wrong, since sound is not a "thing" that flies through the air like a stone (or a feather for that matter). The comparison between the lightning impulse and the tsunami source is much better though - both are, so to speak, impulses that cause a displacement which then propagates as a wave or waves. The water that is displaced by the earthquake is not the same water that makes destructive landfall 1000 miles away. You are asking for one quantity of a medium to pass "through" more of the same medium. This is equivalent to looking at the action of Newton's cradle and thinking that somehow the first ball moves through the others to become the last ball. Now you ~can~ project a stream of water through water; e.g. a powerful underwater water jet; but as we observe, the projected water disperses fairly rapidly into the overall medium just as an human outbreath rapidly merges into the surrounding air. It all "evens out". There is a limit to how far away from a candle you can be and still blow it out. Whereas a sound can be heard miles away from its source, with generally the high frequencies tending to be lost through absorption and diffusion - which is why reverberation in a reflective space loses high frequency energy over time - the more so when there are lots of large humans with clothes, absorbing acoustic energy. They will hear the singer clearly; but they will not feel any air moving past them, because it isn't, unless they are within a few inches of them. Don't just throw any old mathematics around; it has to fit the physics - fit with what is observed and with what is already established about the behaviour of particles, molecules, media, solids, gases, etc. And any experiment you come up with to "prove" your theory must be described in sufficient detail for someone else to replicate it to confirm (or otherwise) the results. You are arguing against established and easily demonstratable physics, so your only possible path to success is a rigorously designed, documented and repeatable experiment. Richard Dobson
From: Richard Dobson on 25 Mar 2010 12:36
On 25/03/2010 02:31, Bappa wrote: ... > Agreed so far? Now we come to the tricky bit. > > Suppose all objects do not have the same speed as the emitter. Like, > I am running to it with velocity v. What will happen, now? > Nothing will happen to the emitter. The emitter is least concerned. > It keeps on emitting! > However, as I am running to the emitter, the disturbance is coming to > me faster. This is the crucial thingy, and let us use water waves as > an example. So, far, so normal - Doppler effect is in play, with varying distance between source and receiver; in your example it is the receiver who is moving. Fine. > You plonk a stone in a pond, and see the ripples going outward. This > is a true wave (unlike the breakers on the shores, which are NOT waves > really and have thoroughly screwed up the world's knowledge of wave > motion). > Okay, so the waves are rippling out. Now, you are on the bank, and by > following a given crest's progression over two fixed marks, you can > find the velocity of propagation of the wave. Agreed? OK ; still normal. > Now let us say you are IN the pond. Right by the first mark (nearer > the shore). As the wave crest reaches the second mark, you swim > towards it with a velocity. > Do you agree, that as you are moving towards it, the crest will hit > you in between the first and second marker? > I think you will do that, or if you do not, a dip in the local pond > with some friendly help will make you see that if you are moving in > the pond, the crests will come to you at a faster rate SIMPLY BECAUSE > YOU ARE MOVING towards them. STILL normal. .... > Now, since the water crests are coming to you faster, so far as you > are concerned, the velocity of the water wave has increased. ~Almost~ normal; but to be precise the ~apparent~ wavelength has changed; or if you like the ~apparent~ speed of the waves has increased. As you say, "so far as you are concerned": this is an illusory increase, not an ~actual~ increase. So the > way you are moving (towards, backwards, sideways) automatically decide > just for yourself what the velocity of the wave is, again, just for > you. And of course, you will find from this example that the > wavelength never, never changes. The wave fronts simply move at a > different rate, and so, you have the corresponding changing > frequencies. > > Well, so much for my insight. Now do I get the Nobel Prize for > Physics, or not??? > No. All you have described is standard Doppler effect, the ~apparent~ change of wavelength caused by (in your example) a listener approaching the source. Nowhere in the above description do you suggest the velocity of propagation itself has changed (your source, the stone, is not even a moving one). That velocity is a property of the ~medium~ (whether water or air); no matter how fast a boat is racing through the water, the speed of propagation of the waves it creates will remain the same. Since you have been claiming that the velocity of sound increases with the velocity of the source, you will at the very least need to include that scenario in your water analogy. But you haven't - you have just described plain standard Doppler effect. Sadly Doppler lived and died before the time of Nobel, otherwise he might well have been awarded the prize. No prizes at all for merely rediscovering it! Richard Dobson |