So no humor or facetiousness is to be allowed on The Dope any more? O.K. sir, got it.
We had better tell that Cecil Adams guy, though.
Not only was it not in any way useful or particularly witty, the comment was conceptually wrong and fundamentally pointless in answering the entirely legitimate question of the o.p. or addressing any subsequent discussion.
Stranger
I think sound and thermal energy are more similar than we are describing. The biggest difference is that the frequencies of thermal energy in solids, in humanly familiar situations, are up in the range we think of as thermal infrared or mid and long infrared. There is also the fact that thermal energy manifests partly in vibration of electrons, so there is often an important electron subsystem, whereas in sound I don’t think there are two overlying populations whose behaviors can be much different. Finally, in gasses, heat energy is stored mostly in short distance linear motion of gas molecules between collisions with one another. It isn’t vibrational in the same sense that sound is, and that heat energy in solids is.
Part of the difficulty is that “sound” is in reality our imposition onto physics of “that which we hear”. I do not think that Chronos is alone in defining it as a mechanical disturbance that transmits through a medium as a longitudinal wave, even though I provided cites that others would define it as any mechanical wave that travels through a medium, including transverse ones (and plate waves and surface waves). The definition is to some degree arbitrary.
What both Chronus’s more limited definition, and my more generalized one, both include however, Napier, is that it is a mechanical disturbance consisting of one or more frequencies. That means a coherent disturbance of something with mass: photons need not apply. Thermal energy as measured by temperature is mechanical but it has no frequency(ies). It can affect the nature of the travel of a mechanical wave through a medium, but it is not a wave or a set of waves, so it is not sound, by either definition. Infrared radiation does not have mass and therefore is not a mechanical wave; it therefore is not sound. It also is not able to be measured as the temperature of a substance, so is not what the op was thinking of as “heat”, even if it causes such once it interacts with objects of mass.
That harkens to the basic problem with considering heat a “vibration”; you are talking about frequency spectra of radiated energy, which is not “heat”. Radiation will have a flux isosurface (a surface around the radiating object in which the energy level is equal) that is readily definable by gemoetry, and a body of known greybody or spectral emissivity properties will radiate “randomly” across a defined spectra. (By random, we mean that the properties and distribution of any individual photon that is radiated are predictable only across a statistical distribution, but the sum of a large population of photons will fit that distribution exactly to within confidence and error measurement limits.) But within the boundary where the heat energy is contained, there is no specific wavelength of heat energy reverberating, and it is generally wrong to think of electrons as vibrating like random particles insofar as their interactions occur in quanta as described by quantum electrodynamics.
In contrast, most bodies will resonate acoustic sound waves (mechanical vibrations in the solid or fluid media which occur at the molecular or solid grain level with essentially no quantum effects) at or around a few peak frequencies, radiating sound at characteristic wavelengths. Getting an acoustic response that is truly evenly distributed, like a uniform “white noise” or some other continuous spectra like “grey noise”, is really physically difficult, whereas with radiation from a heat source, the continuous distribution defined (approximately) by the Rayleigh–Jeans law (for thermal wavelengths) or Planck’s Law (across all wavelengths).
Stranger
Chronus, a question to clarify our different understandings:
The classic kids two cans attached by a taut string bit. The longitudinal wave is transduced into a transverse wave along the string and then transduced back into longitudinal waves at the other can. Is it your position that it is not sound while it is being transmitted along the string?
Stranger, I gotta tell ya, “sound is louder” provided more clarity, to me at least, than that last post. Do you mind trying to dumb your point down a little so I can better get what you are meaning?
The mechanisms that make what we think of as “sound” are not anything like the mechanisms that create what we think of as “heat”. Sound waves come in distinct chunks of the acoustic spectrum dependent upon the source. Radiation from a heat source, by definition, is distributed smoothly across the thermal part of the electromatic spectrum and is dependent only upon the temperature of the body and its emissivity characteristics.
Stranger
This is not what occurs. In the two-cans-with-string “phone”, the sound waves remain longitudinal. The string has to have tension for this to work, and the sound waves are propagating changes in that tension.
Still, you could probably set up a system where you did transmit sound using a transverse wave. I think it’s a question of semantics whether you will only consider longitudinal waves to be sound waves, although Googling around, it seems most definitions, if not all, did specify longitudinal waves. If you take one of those definitions for sound, then (by definition) it wouldn’t be sound while it was being transmitted as a transverse wave.
For the OP, I’d say that sound can be a component of heat.
When a material has heat, it has energy due to the material not being in its ground state. That energy is in a variety of forms, and is distributed randomly among all the possible forms it could be in. In a solid, you’d have longitudinal and transverse vibrations. In a gas like air, with diatomic molecules, some energy is in rotations of the molecules, and other energy is in the motion of the atoms or molecules. Some energy is in photons as well.
In all cases, some portion of the heat energy is in longitudinal waves, and is legitimately called sound. It doesn’t matter that it has a small amplitude, or that it doesn’t have tones like music or structure like speech, it still fits the definition of sound. Some portion of heat energy is in other forms, and so isn’t sound.
Of course, when you do have musical notes or speech, that’s not heat. The energy is only certain frequencies, and isn’t in thermal equilibrium with photons, for example. So in brief, all sound isn’t heat, and all energy of heat isn’t sound, but there is some overlap.
If you had a system where the vibrations were converted to transverse waves and then back (and I’m sure such a system could be contrived, even if the tin-can phone isn’t it), then I would say that no, it isn’t sound while it’s on the string.
And no big deal, but my name has two Os and no U.
Sorry for the misspell and thanks for the answer … and I’m quite confident that the string under tension is vibrating transversely not transmitting vibration in a longitudinal compression wave as if through a hollow tube.
And also thank you, Stranger for the simpler presentation.
Imagine two circular cans, with the string attached in the center of each can, with the sound coming straight into the can, so the whole setup has circular symmetry. What would break the symmetry to cause the string to vibrate transversely in one plane? Or would you expect this to not transmit sound?
DSeid and Stranger, I think you misunderstand. Whether sound or heat energy include single frequencies or an undifferentiated combination of frequencies doesn’t matter. Heat energy generally contains a wide range of frequencies and might be thought of as a noisy sort of sound as opposed to a tone. I mention the thermal infrared in the context of frequencies, meaning the neighborhood of 10^12 to 10^14 Hz, and in fact the frequencies of thermal radiation are typically in this range because the atomic vibrations themselves are. You can be interested in the atomic vibrations and note they contain much of their energy in the range 10^12 to 10^14 Hz, without confusing infrared radiation and heat energy. It is the same thing as saying the wood of a guitar body vibrates at frequencies that are typical of music, without having to maintain that the vibrations are music while still in the wood.
With a string under tension sudden changes in length create transverse displacements. I think it has something to do with Poissons Law but I am not sure.
Do the experiment - create a tin can phone. Listen while someone talks on the other side. Observe the string vibrating transversely. Then have someone tightly clamp the middle of the string preventing transverse vibration (or squeeze some heavy modeling clay around it) and observe the volume of what you hear decrease.
Or just take a rubber band and stretch it and rhythmically stretch and release and the band bounces.
Or do the reverse - in your system vibrate the string transversely, does sound get produced in your cans? Why? Why would transverse displacement of the string cause longitudinal displacement of the flat surface of the can and then the air?
If you have an isolated system (e.g. a piece of metal floating in a vacuum) and give it a knock, so it vibrates, like a tuning fork, those vibrations are sound. Eventually the energy will be converted to heat. Is there a clear distinction between the 2, or do they overlap, like our division of the electromagnetic spectrum?
I’ve given more thought to this matter:
I get what you mean, and it makes sense, but I don’t know if it’s true. You’re saying heat is the distribution of velocities (including direction as well as speed), while sound has a narrower velocity profile. But I don’t know when one changes to the other.
I don’t think heat is only definable for a large number of atoms though. For ideal gases, their temperature, and hence thermal energy, depends only on the kinetic energy or speed of the particles.
How about this: if you microwave a bowl of water, the atoms move pretty coherently, like the definition of sound. So is it hot or just 2.4 GHz sound?
One distinction I can think of is heat is not only contained in motion, but also in rocking, wagging, stretching of atomic bonds. Perhaps we should only consider ideal gases when pondering this matter.
Not really. The molecules that are directly affected by the microwaves will be pretty coherent, but they’ll give up their energy to their neighbors pretty quickly, and in the process decohere.
DSeid, I think you’re probably right. Between the droop in the string from gravity, the cans not held perfectly straight, and talking into the can at some angle, there’s opportunity for transverse waves to be set up. So you’d have three transmission “channels” (two transverse waves and one longitudinal), all excited in some amount. In my hypothetical (and assuming it’s done on the ISS, so there’s no droop), you’d only have the longitudinal wave, but that’s not the general situation. Maybe I’ll try the experiment anyway.
AaronX, see my post 29. Heat isn’t just sound because some of the energy is in other forms than sound. Sound isn’t just heat because the energy isn’t randomly distributed.
In your example of hitting a bar floating in a vacuum, you initially have a lot of energy in a few vibration modes, plus heat energy randomly in all the other modes, as well as some in photons, due to whatever the bar’s initial temperature was. As time goes on, the vibrating modes have less and less energy, with the rest of the modes and the photons gaining a little energy, so after time passes, the bar’s heat increases a little. But those vibrating modes still have a little energy in them.