On a molecular level, how exactly do sound waves go around corners? Is it just that the pressure of the more central parts of the wavefront forces the particles on the outer edge to expand out?
>>7932879
Also how does the slit being less /wide/ than the wave's /length/ lead to diffraction when these quantities are perpendicular to each other?
>>7932886
It's always radial
>>7932945
Plane waves aren't radial and they go around corners too
Anyway I'm asking about the molecular level
>>7932960
Plane sound waves don't exist, that pic on the left is bullshit for sound
At a molecular level you're just changing density, so they are oscillating between bumping into each other more and less
It's like fluid mechanics OP. Sharp corners with a lower pressure will pull the higher pressure in that direction.
>>7932965
>At a molecular level you're just changing density, so they are oscillating between bumping into each other more and less
Well that might be how sound in general works but I'm asking how a sound wave goes around corners, at the molecular level. Particularly a plane wave. Seems like all the energy should be going straight ahead, but if the inner sections of the wavefront have higher pressure then it will force the outer edge to expand into the relatively free space next to it.
For future reference BTW "waves expand radially" is a description, not an explanation
>>7932983
Cheers bruh that's what I was looking for.
>>7932983
Can you help me out with this too?
>Also how does the slit being less /wide/ than the wave's /length/ lead to diffraction when these quantities are perpendicular to each other?
>>7932879
This is a tough one. Thank you for asking it. Now i finally get it too. I borrow the words of the David G Grier because I never could explain it as clearly.
"""The idea is that each point along the wavefront of a wave acts as a discrete source of spherical waves. Each of these conceptual point sources, moreover, oscillates at the frequency, amplitude and phase of the wave at that point. The coherent superposition of the waves emanating from those conceptual point sources creates the three-dimensional wave that propagates onward.
In a plane wave, for example, the superposition of spherical waves from all of the points along the wavefront has precisely the phase relationship needed to recreate the next planar wavefront in the train of wavefronts.
The presence of an obstacle such as the corner of a wall eliminates some of those conceptual point sources. The spherical wave emanating from the point source right at the corner therefore propagates outward as a spherical wave, and thus propagates around the corner.""" David G Grier - New York University
>>7933316
>>7932879
So, as I get it. Spherical wave is always there, it is just hiding under superposition principle. Corner or slit remove those oscillating particles from either side revealing the spherical shape of the wave front. The amount of spherical waves in plane wave hides the fact that there are any.
>>7933001
>Cheers bruh that's what I was looking for.
no, it wasn't
this has nothing to do with your problem
>>7933414
Actually huygeb's principle could make sense just from the electrons on the wavefront pushing forward since that would generate a wave of radial force from every point
>>7932879
>>7933316
>>7933322
One of the most enlightening courses I took as an undergrad was statistical mechanics. The approach it takes is lots of little atoms bouncing around and on average certain behavior can be observed.
When a sound source propagates a wave, The atoms bounce off themselves like little billiard balls. Very few (if any) are precisely radial to the source. Some are ejected a little left, some little right of the collision. On average the overall wave front from the source is radial (i.e. circular from the source).
>>The idea is that each point along the wavefront of a wave acts as a discrete source of spherical waves. Each of these conceptual point sources, moreover, oscillates at the frequency, amplitude and phase of the wave at that point. The coherent superposition of the waves emanating from those conceptual point sources creates the three-dimensional wave that propagates onward.
This is basically saying that each point in the wave front acts as its' own source of emanating waves. If every other point nearby ceased to emanate new waves it would look like a new source. As long as other sources exist from the original source are viable, it will average out to a wave front radial from the original source.
With this frame work in place:
- The slit eliminates other wave fronts and creates a new "source". Hence waves beyond the slit are radial about the slit.
- In the corner case there actually is a mix of radial waves emanating from the corner plus radial waves emanating from everything away from the corner. So this a more complicated situation than a simple slit. But bottom line is the corner would behave as a new source plus the additions from sources away from the corner.
>>7933466
>This is basically saying that each point in the wave front acts as its' own source of emanating waves.
That is simplification of how Huygen's principle is often interpreted. Even though explanation is not exact, it helped me to realize what I missed. Specially the removing the obstacle part. You are right though, underlying mechanics is more complicated than that.
>>7932879
>Speaker provides kinetic energy to air molecules
>Air molecules travel
>Air molecules hit the wall
>Largely inelastic collision
>Momentum is conserved
>Air molecules that impact the wall are now stationary
Simple really.
>>7932886
Huygens principal. The slit acts as a source of secondary wavelets, so it acts as if there are in fact two sources instead of one. This then leads to constructive and destructive interference.
