Like I get that for longitudinal waves the atoms vibrate parallel to the direction of travel, but why does not allow the waves to be polarised? Each sound wave can move in any 3 dimensional plane, right? Because when sound is emitted from an speaker, you can hear it 360 degrees around the object, it doesn’t only move forward or backwards, so whats the catch?
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Theres probably something I am missing here, but all the websites ive checked only give cookie cutter answers to this question. Thanks!
In: Physics
We live in 3 dimensional space. X-axis, Y-axis, and Z-axis. A longitudinal wave traveling along the Z-axis will cause vibrations along the Z-axis. There is no other axis which is parallel to Z.
A transverse wave traveling along the Z-axis can cause vibrations on the x-axis or the y-axis. Since there are two options, they can be polarized by being one or the other.
Transverse waves have something to differentiate them and longitudinal ones don’t.
If you look at the waves head on. The transverse wave has something going on across your line of sight that makes them not symmetric. The longitudinal wave doesn’t have that and lack an orientation. As an analogy, imagine throwing a frisbee. I can use a slit that only allows the frisbees spinning horizontally or vertically (or anything in between) through and only have “polarized” frisbees on the other side. I can’t do that same thing with basketballs and a hole since a horizontally and vertically spinning ball both fit through the hole.
WHen waves travel in free-space they are transverse. This is the situation normally studied. When waves are not transverse, they are very complicated. In such a case, it doesnt make sense to say its polarised. Rather, it has some specific complicated field pattern.
For example, when a wave travels through a wave-guide, it is described as being in a waveguide **mode.** You cant talk of polarisation unless the mode is transverse and simple.
For example, take a look at some of these modes:
[https://en.wikipedia.org/wiki/Transverse_mode#/media/File:Selected_modes.svg](https://en.wikipedia.org/wiki/Transverse_mode#/media/File:Selected_modes.svg)
[https://en.wikipedia.org/wiki/Transverse_mode#/media/File:Laguerre-gaussian.png](https://en.wikipedia.org/wiki/Transverse_mode#/media/File:Laguerre-gaussian.png)
Now whats the polarisation of *that*?!
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