In reply to Jones Beene's message of Tue, 29 Nov 2005 13:36:40 -0800: Hi, [snip] >Robin, > >> If sound and heat are the same phenomenon, then why is the speed >> with which heat is conducted through a solid so much lower than >> the speed with which sound is propagated? > > >Why would you assume that it is lower? It isn't always.
Name one solid where this isn't true. > >And why would you assume that they are the same? Misunderstanding. On the previous line they had been grouped together leading me to assume that you meant they were the same phenomenon. I was contesting that notion. However from your question here above, it is apparent that you only grouped them together because both were related to phonons. (BTW I think heat is also related to the free electrons in metals). >Both are lesser >included subsets of "kinetic" wave-forms in matter (phonons), but >are different in the details - while they can appear similar in >those spectrums where there is overlap. > >Given that some materials are "sound-proof" but still transfer the >kinetic component of heat - the opposite [for speed of transfer] >is true for them. I can think of only one somewhat artificial example:- a substance that contains tiny "sonic diodes" which convert sound into a flow of air, thus preventing it from passing in the form of sound. Since such a substance could be made of metal, it would still conduct heat. (BTW this actually exists). However it doesn't really meet my definition above. > >"Heat" is normally much higher frequency than sound and applies to >both phonon and photon radiation, yet cannot always be heard >(unless there is a harmonic below about 18 kHz) - but that does >not mean it is always propagated "slower." Actually, I don't think I've ever heard heat. >Sound cannot always be >heard but the frequencies of even ultrasound are much longer than >"heat". Presumably you meant wavelengths. >ERGO it is "different" in propagation speed, but not >always "slower" due to the fact that heat is broad spectrum, has >BOTH kinetic and photonic waves, while sound is narrower spectrum, >lower frequency, non-photonic, and often much more intense at any >given frequency - and consequently the transfer-medium is more >likely to resonate in bulk at that lower frequency, so the >apparent speed seems higher - since the wavelength is much longer. I suspect it has more to do with the frequencies at which the atoms/molecules within the substance resonate. Where resonance exists, energy is absorbed rather than being passed on, which results in the wave front being slowed. Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition provides the motivation, Cooperation provides the means.
