I apologize if this is a naive question, but I never really learned about this. I'm curious as to what happens to sound waves after they are "used"? For example, if I say something to you verbally, then a sound wave is transmitted and picked up by your ears, but what happens to the wave after that? Does it float away into space? And if sound waves are never destroyed (not saying that is the case, but if it is), does this theoretically mean we can reproduce or attain all sound waves from the history of man, including every word ever spoken?
[Physics] What happens to sound waves
acousticsperceptionwaves
Related Solutions
I think the question is too complex to give a satisfactory answer without deep study of the problem. The biggest problem is that there are several ways how vibrations (sound waves) travel from the source to the receiver. The path of the excitation: the source - glass - fluid - glass - the receiver you've described is only one one possible path. Some of the excitation shall travell through glass only, e.g. bottom or side of the glass.
So if you want to have exact solution you should find standing sound wave (eigenfunction) solution of the whole system glass + fluid, which is far from being trivial. Of course, in this case you must also consider dissipation, because you have constant excitation and without the dissipation the vibrations would continue to grow to infinity.
The second possible, more engineering way to get the answer is to disregard sidepaths of excitations and calculate in terms of traveling sound wave. At one end you have the source, excitations first travel through glass, then difract on the border between glass and liquid, travel throught liquid, again difract on the border between glass and liquid and finally travel through the glass to the receiver, where all of the wave energy is absorbed.
In both cases you need speed of sound in medium, which is not hard to obtain:
$$v^2 = \frac{E}{\rho} = \frac{K}{\rho},$$
where $\rho$ is density of the medium, while $E$ is Young's modulus (solid) and $K$ is bulk modulus (liquid). In the second case you also need transmitivity, which is of course dependent on the incident angle and you can find the right equations by peaking at Fresnel equations.
I hope I understood you right and that my answer helps.
Yes, the frequency is normally the same.
If the sound is reflected from a moving object then the frequency will be shifted higher or lower depending if the object is moving towards or away from the observer. This is the Doppler Effect.
I have assumed that the observer emits the sound and is not moving. If the observer is moving towards the reflector or away the frequency will also be shifted higher or lower.
If for the example the observer is emitting sound and moving away from the reflector then the frequency of the sound reflected back will be lower. To calculate this there are two steps. First, the frequency, $f$ received by the stationary reflector needs to be calculated with the doppler formula
$$f={c \over c+ v_s} f_0$$
where $f_0$ is the original frequency, $c$ is the speed of sound in air and $v_s$ is the speed of the source moving away from the reflector.
Now the frequency, $f'$, observed by the moving observer is given by
$$f'={c - v_o\over c } f$$
where $v_o$ is the speed the observer is moving away from the reflector.
Now putting the two equations together and remembering that the observer is the source of the sound (so that $v_s=v_o$) we get
$$f'={c - v_s\over c } f = {c \over c+ v_s} f_0$$
$$f'={c - v_s \over c+ v_s} f_0$$
Best Answer
No, It's not possible. Sound ultimately transforms into heat energy. You can not reproduce all the useful and useless sounds from history. In general all energy is ultimately converted to heat energy and heat energy flows from an object at higher temperature to an object at lower temperature in order to attain thermal equilibrium.