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Hot answers tagged acoustics

4

The source "launches" wave fronts at a given frequency, but it launches each one from a new location. If the source is moving toward the observer, each new wave front is launched from a location closer to the observer than the last, and so takes less time to reach the observer than the previous one. So, the time between wave front arrivals at the observer ...

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The waves do just 'add-up' their amplitudes, so that where two peaks combine you get a larger peak, where a peak combines with a trough the two amplitudes cancel, and where the two waves are both zero you get zero amplitude. Because the two waves have different frequencies, the alignment of their peaks and troughs varies over time in a way that isn't equal ...

2

Do it in the vacuum. Since sound is the mechanical wave, you just need to prevent it from propagate mechanical vibration to your ear. Reference: https://en.wikipedia.org/wiki/Sound

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hammering on a wall will transmit the sound vibrations much more strongly than playing a recording of hammering towards the wall, even at the same volume level in the room. This is because instead of the sound waves hitting the wall, the hammer itself is hitting the wall and so the displacement waves are being fed directly into the wall structure.

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The wall is acting just like a sound board which is part of a stringed musical instrument, exciting a larger volume of air and hence producing a louder sound. When you hit a nail you send (compression) pulses through the nail which are either reflected at the interface between the nail and the medium outside or are transmitted through the interface. ...

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This could be thought of in terms of the impulse response of the wall. If the impulse response was non oscillatory (say, a decaying exponential) then the sound on the other side would be a low pass filtered version of the impinging wave--whether it is an impulse or something else. Otherwise the wave on the other side could include the resonant ...

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You are absolutely right that humidity plays a large role in acoustic attenuation, like the plot below shows. While you did ask for a more complete explanation, I should warn you that the physics behind this are non-trivial. I'll try to make it as easy as I can, though. There are three mechanisms of attenuation in air. They are viscosity, thermal conduction,...

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Gravitational waves carry energy, momentum, and angular momentum away to infinity, thereby damping the ringing and allowing the merged hole to settle down into a Kerr metric. The amount of energy radiated can be enormous... a significant fraction of the mass-energy of the merging black holes. For the first LIGO event, three solar masses was lost as ...

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Re. "Is this what happens to real sounds waves as they attenuate" Yes: a pulse tends to become less oscillatory as it propagates through a medium that attenuates as a function of frequency and also gets stretched out in time. An FIR filter should be a good model of this. For example if you convolve a single cycle of a sine wave with wave length l with a ...

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There will always be some sound produced when you pour the water. You can just slowly pour the water along the sides of the container and the sound produced will be almost inaudible.

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If the propagation of sound waves and light waves are governed by exactly the same wave equation: $$\frac{\partial^2 f}{\partial t^2}=c^2 \nabla^2f,$$ where $c$ is the propagation speed of the waves and $f$ is the thing that propagates (say, pressure for a sound wave or electric field for a light wave) why can you hear but not see what’s happening on the ...

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For the sake of this argument, imagine an infinitely thin barrier (or a thick barrier with a very sharp corner, if you prefer). Think of a molecule right at the edge of the barrier but not touching it. A sound wave approaches. What this means is that the nearest neighbor molecule behind it is approaching. It may hit straight on and accelerate the ...

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It is not quite clear to me what you are asking, but I would refer to simulations like on PhET: Wave Interference. There you can switch between sound waves, surface waves on water (ripple tank) or light waves. There are two important things to realize: The wavelength of sound waves is of the order of 1 meter, comparable to the height of walls. We ...

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There are three types of waves in a thin rod - longitudinal, bending (transverse), torsional. The velocity of propagation of longitudinal waves in the rods is equal $$c=\sqrt {\frac {E}{\rho}}$$ The dispersion equation of longitudinal waves is $$\omega =ck$$ In this case, the frequency does not depend on the diameter of the cylinder. For bending waves of ...

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The effects of decreased density and decreased pressure with altitude actually cancel each other out! And so, in some sense, gravity doesn't affect the speed of sound much at all. However, the higher up you go, the lower the temperature is (which is related to the low density of the atmosphere). So in fact, the speed of sound decreases. Here is a ...

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