Why is the speed of sound the limit to which air can be accelerated in a nozzle without a diverging section? Why sound, instead of, say, electromagnetic waves, or some arbitrary constant determining the "speed limit" of particles?
What is the relationship between sound (pressure waves) and matter with respect to velocity?
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Molecules don't travel as electromagnetic waves.
The speed of sound is the limit because that is how fast the particles travel.
What kind of non-answer is that?
Molecules don't travel as pressure waves, either, not in this context. We are talking about a mass flow of air that cannot be accelerated past a certain point without a change in geometry, due to a handful of equations, choked flow, etc etc.
My question is why is that certain point related to "the speed of sound", or the speed at which an infinitesimally small pressure wave would propagate itself through a medium. Why sound? What's the special relationship with sound and the mass flow we are trying to accelerate?
Because the nozzle is effectively the same as a pressure wave traveling through the medium.
Imagine the air is stationary and the nozzle is moving, the physics are exactly the same and so is the wave.
Perhaps it's down to the sound waves and the air which is "transmitting" these sound waves suddenly travelling at the same speed and sort of crashing with each other. Maybe akin to feedback of some sort.
So it's because we treat the matter as it moves similar to a wave? I suspected that had something to do with it. Does this have anything to do with wave-particle duality, or is it unrelated?
You're looking at it backwards. Sound is just the acceleration of particles caused by fluctuations in pressure, so of course that's going to be the limit. The acceleration limit is the reason sound travels at the speed it does, not the other way around.
>Does this have anything to do with wave-particle duality, or is it unrelated?
Unrelated, Wave particle duality is some seriously weird shit that doesn't really make sense to me even though I know it is true.
Ohhh...I thought sound was the pressure difference (wave) itself. Sound is the actual acceleration of particles due to the pressure wave?
Because if you start with a medium at rest and introduce a small disturbance, the information about that disturbance, the energy introduced, will radiate away through the medium as a pressure wave. The speed of that wave is the speed of sound. These waves are nice and simple, near equilibrium, small disturbances, don't interact with each other.
If an object moves subsonic through air, its presence will be felt/heard before it arrives and the disturbance it creates is radiated away in all directions.
When something moves supersonic through air, it slams into unsuspecting air with no warning and keeps ramscooping everything in its path, which creates a huge shock wave. It breaks all the nice near-equilibrium small-disturbance stuff because it is moving faster than the medium can handle information.