For a sound wave how/why does the compression and rarefaction occur?

In summary, the high pressure wave moves across the medium and causes an area of low pressure. This low pressure then causes the air to move in a high pressure direction, and this continues until the high pressure wave reaches the other side of the medium.
  • #1
hongiddong
65
1
I cannot seem to visualize how this compression and rarefaction occurs for example when I clap my hands, I know I move air molecules away from me, but it's so weird that such compression(high air pressure) and rarefaction(low air pressure) occurs. I also do not quite understand why this phenomena occurs.

Maybe somehow the clap creates a region where there is a high air pressure due to more air molecules leaving the area adjacent to it causing a cascade effect in which the air molecules move in this direction: high<---low, but we also get this direction of air movement low---> high, how does a sound wave continue to cascade the air molecules through space in this high<---low---> manner?

I am really confused? Please, I need help understanding this?
 
Physics news on Phys.org
  • #3
Wow that helped a lot.

Can I ask you if I now have the right understanding. A high pressure(amplitude of the wave)' moves across the medium, in which as it moves, causes areas of low pressure, but as it continues to move,the area that had high and low pressure comes back to normal. And this is all happening at the speed of sound, 340m/s ? The medium only moves side to side, so the first high pressure simultaneously causes a low pressure to form, and as the air goes back to status quo to fill the low pressure again, we create another area of low pressure and high pressure?

Thanks so much Daven.
 
Last edited:
  • #4
hongiddong said:
Wow that helped a lot.

Can I ask you if I now have the right understanding. A high pressure(amplitude of the wave)' moves across the medium, in which as it moves, causes areas of low pressure, but as it continues to move, the area that had high and low pressure comes back to normal.

Yes

And this is all happening at the speed of sound, 340m/s ?

Yes, give or take a bit, different mediums, depending on their density, have different velocities
here's one small list ... am sure you could google others say for wood etc :smile:

The medium only moves side to side, so the first high pressure simultaneously causes a low pressure to form, and as the air goes back to status quo to fill the low pressure again, we create another area of low pressure and high pressure?

Thanks so much Daven.

careful with your terminology there :wink:
a side to side movement is known as a traverse wave. where the particles of the material are moving sideways ( at 90 deg to the direction of travel of the wave)

a sound wave = a compressional wave and it moves back and forwards along the direction of travel of the wave as in the animation

cheers
Dave
 
  • #5
I am just confused with one last part to this. I see that the high pressure moves, however, I don't understand how that high pressure and low pressure keeps propagating. The medium itself does not propagate, but it vibrates in a parallel manner.

I at first thought that the initial high pressure or that pocket of the initial air kept moving across space.

The medium moves parallel to the propagation, so the first high pressure simultaneously causes a low pressure to form, and as the air goes back to status quo to fill the low pressure again, we create another area of low pressure and high pressure? I am still a bit confused.

Thanks Dave for all your help. I am definitely starting to get it.
 

1. How does a sound wave travel through a medium?

Sound waves travel through a medium by causing the particles of the medium to vibrate. This vibration creates a disturbance that moves through the medium in the form of a wave. The particles in the medium move back and forth in the direction of the wave, transferring energy as they do so.

2. What causes the compression and rarefaction in a sound wave?

The compression and rarefaction in a sound wave are caused by the rapid change in pressure created by the vibrations of the medium. As the sound wave travels, it causes the particles in the medium to compress together, creating a region of high pressure. This is followed by a rarefaction, where the particles spread out, creating a region of low pressure.

3. How does the frequency of a sound wave affect the compression and rarefaction?

The frequency of a sound wave determines how often the particles in the medium vibrate. As the frequency increases, the particles vibrate more rapidly, resulting in shorter distances between compressions and rarefactions. This means that there will be more compressions and rarefactions in a given amount of time, resulting in a higher pitch sound.

4. Why do sound waves need a medium to travel?

Sound waves need a medium to travel because they require particles to vibrate in order to transfer energy. In a vacuum, where there are no particles, sound waves cannot travel. This is why sound cannot travel through outer space where there is no medium.

5. How does the amplitude of a sound wave affect the compression and rarefaction?

The amplitude of a sound wave determines the amount of energy it carries. As the amplitude increases, the particles in the medium are pushed farther apart during compression and closer together during rarefaction. This results in a larger difference in pressure, creating a louder sound.

Similar threads

Replies
8
Views
2K
Replies
35
Views
4K
Replies
20
Views
4K
Replies
3
Views
2K
Replies
44
Views
5K
Replies
30
Views
561
Replies
49
Views
3K
Replies
10
Views
961
Replies
8
Views
742
Back
Top