Do sound waves carry momentum?

In summary, the conversation discusses whether sound waves carry momentum. While it is commonly known that they carry energy but not momentum, there is a debate about whether they theoretically have a very small amount of momentum similar to light. Some argue that sound waves are made up of vibrating molecules, which have momentum, while others point out that the properties of materials that affect light transmission are well understood. The concept of a luminiferous aether is also mentioned. It is acknowledged that sound waves in a crystal lattice are quantized and have a momentum, but there is difficulty in visualizing the momentum of an acoustic wave with a classical approach. The conversation also touches on the idea of phonons carrying pseudomomentum and the different velocities of sound waves. Overall
  • #1
granpa
2,268
7
do sound waves carry momentum? any momentum at all (no matter how small)?

the obvious answer is that they carry energy but not momentum but i am wondering whether they don't theoretically carry some very tiny (usually negligible) amount of momentum in the same way that light, even though it can normally be thought of as being massless, theoretically does have some very tiny amount of mass.
 
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  • #2
sound waves are vibrating molecules, and everyone of these molecules move and thus have a momentum.

Hey I got an idea, if we can get a formula for momentum for sound, ie vibrating particles, then we can use it the other way round to determine the properties of the "medium" that light eventually travels through, right? ;)
 
  • #3
Kurret said:
sound waves are vibrating molecules, and everyone of these molecules move and thus have a momentum.

Hey I got an idea, if we can get a formula for momentum for sound, ie vibrating particles, then we can use it the other way round to determine the properties of the "medium" that light eventually travels through, right? ;)

Wrong, light does not propogate in the same manner as sound. The properties of materials which effect light transmission are pretty well understood.
 
  • #4
Okay so do sound waves have momentum or not? I believe they do...as do light waves.

I know sound waves move a lot like a wave and light as a wave function consisting of particles (photons) thus having a wave-particle duality.
 
  • #5
Uhm... sound waves in a crystal lattice are quantized and can be seen as "phonons" which definitely have a momentum (equal to hk, if I remember correctly).

However I seem to have some problem in seeing the momentum of an acoustic wave with a classical approach. :/ There are certainly cases where an acoustic wave can "push" an object, for example in the case of a "shock wave".
 
  • #6
or better yet, bass frequencies...

you can "feel" bass
 
  • #7
Integral said:
Wrong, light does not propogate in the same manner as sound. The properties of materials which effect light transmission are pretty well understood.
It was more like an idea IF there is a medium that light travels through (not any "material"), but more like the luminiferous aether that people thought existed a while ago. Do we really know everything about the properties of light? I doubt that.
 
  • #8
Domenicaccio said:
Uhm... sound waves in a crystal lattice are quantized and can be seen as "phonons" which definitely have a momentum (equal to hk, if I remember correctly).

Phonons carry pseudomomentum. Summed up, the momentum of all phonons usually cancels to 0. Otherwise the center of mass of the crystal would have to move.
 
  • #9
Sound waves have momentum and dispersion, a phase and a group velocity. That's one of the reasons why gongs, when struck with a soft mallet, have long attacks.
 
  • #10
Domenicaccio said:
Uhm... sound waves in a crystal lattice are quantized and can be seen as "phonons" which definitely have a momentum (equal to hk, if I remember correctly).

However I seem to have some problem in seeing the momentum of an acoustic wave with a classical approach. :/ There are certainly cases where an acoustic wave can "push" an object, for example in the case of a "shock wave".


same here.
 
  • #11
NYSportsguy said:
I know sound waves move a lot like a wave and light as a wave function consisting of particles (photons) thus having a wave-particle duality.

sounds pretty dumb to say sound waves move a lot like a wave when sounds waves are in fact waves... why do you think they call them sound WAVES haha... of course this coming from a yankee fan... haha just bustin your balls
 

1. How does sound carry momentum?

Sound waves carry momentum through the transfer of energy from one molecule to another. When a sound wave travels through a medium, it creates vibrations that cause the molecules in the medium to move back and forth. This movement of molecules transfers energy and momentum from one molecule to the next, allowing the sound wave to travel through the medium.

2. Is sound a form of matter that carries momentum?

No, sound is not a form of matter. It is a form of energy that travels through matter. However, the transfer of energy and momentum through sound waves can affect the movement of matter in a medium.

3. How is the momentum of a sound wave calculated?

The momentum of a sound wave is calculated by multiplying the speed of the wave by its mass. The speed of a sound wave is determined by the properties of the medium it is traveling through, such as density and elasticity. The mass of a sound wave is determined by the amount of energy it carries.

4. Can sound waves carry momentum in a vacuum?

No, sound waves cannot travel through a vacuum because they require a medium, such as air or water, to travel through. Without a medium, there are no molecules for the sound wave to transfer energy and momentum to.

5. How does the momentum of sound waves affect objects in their path?

The momentum of sound waves can cause objects in their path to vibrate or move. For example, when sound waves hit our eardrums, they cause them to vibrate and allow us to hear. Additionally, loud sounds can cause objects, such as windows or dishes, to vibrate and potentially break due to the transfer of energy and momentum from the sound wave.

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