# Sound waves propagated as transverse waves

• koat
In summary: Recently the people of Haiti and Chile called them earthquakes. They are all too real.Did you read my linked thread?If you don't understand the difference between shear and normal force then try this explanation.In a fluid (liquid or gas) the particles are distributed at random as in my first sketch. They can move freely in any direction and there will be local 'clumps' where the molecular density is temporarily higher or lower than average.A pressure or longitudinal wave is nothing more than organising these clumps to form a regular pattern of higher and lower density (pressure).In a solid there is a regular array and the molecules are not free to move about. Instead they can 'vibr

#### koat

hello
can somebody tell me why sound waves can't be propagated as transverse waves?

koat said:
hello
can somebody tell me why sound waves can't be propagated as transverse waves?

Welcome to the PF. Tell us your thoughts on the question. What is sound? What kind of waves generally propagate sound? What kind of things are propagated by transverse waves? Can you see anything at the molecular level (in air or water or solids) that would affect how sound is transmitted?

EDIT -- this sounds a bit like schoolwork, so you need to show some effort at helping to figure out the explanation.

Who said they can't?

Studiot said:
Who said they can't?

my textbook

berkeman said:
Welcome to the PF. Tell us your thoughts on the question. What is sound? What kind of waves generally propagate sound? What kind of things are propagated by transverse waves? Can you see anything at the molecular level (in air or water or solids) that would affect how sound is transmitted?

EDIT -- this sounds a bit like schoolwork, so you need to show some effort at helping to figure out the explanation.

I have no idea :(
I just know that water waves and waves in the em spectrum are transverse waves

Think about how a transverse wave propagates. For this example, don't worry about EM waves (which propagate differently than sound), just consider transverse waves moving down a string as you oscillate one end of the string up and down. What force makes the string as a whole propagate the wave? Why is it that when I pull up on one side of the string, other pieces of the string also move up?

Is this force present in air?

koat said:
my textbook

if that's true, your textbook is using a restricted definition of sound waves.

Sound waves in a gas cannot support transverse waves. This is because a gas is not resistant to shear forces. berkeman asked about molecules. What are the properties of molecules in a gas, and what is shear force?

Sound waves in a solid can be transverse waves.

Phrak said:
Sound waves in a gas cannot support transverse waves. This is because a gas is not resistant to shear forces. berkeman asked about molecules. What are the properties of molecules in a gas, and what is shear force?

Sound waves in a solid can be transverse waves.

In a gas the molecules are further apart than in solid.
But I don't understand why there are transverse waves in the solids...

Phrak said:
Sound waves in a gas cannot support transverse waves. This is because a gas is not resistant to shear forces. berkeman asked about molecules. What are the properties of molecules in a gas, and what is shear force?

Sound waves in a solid can be transverse waves.

why is gas not resistant to shear forces?

koat said:
why is gas not resistant to shear forces?

This is a classwork question so you have to do some work first. What is a shear force?

Phrak said:
This is a classwork question so you have to do some work first. What is a shear force?

is it a force that pushes something?

But I don't understand why there are transverse waves in the solids

Recently the people of Haiti and Chile called them earthquakes. They are all too real.

If you don't understand the difference between shear and normal force then try this explanation.

In a fluid (liquid or gas) the particles are distributed at random as in my first sketch. They can move freely in any direction and there will be local 'clumps' where the molecular density is temporarily higher or lower than average.
A pressure or longitudinal wave is nothing more than organising these clumps to form a regular pattern of higher and lower density (pressure).

In a solid there is a regular array and the molecules are not free to move about. Instead they can 'vibrate' about their mean positions, as dictated by the bonds with their immediate neighbours.
Vibration along the bonds axes is energetically preferred.

So if we can organise a wavetrain of vibrations to pass down the array it can be either longitudinal or transverse as shown.

#### Attachments

• wave1.jpg
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koat said:
is it a force that pushes something?

Search on "shear wave" and there will be a Wikipedia article. Go to the article. The first animated picture is a shear wave.

Note, it might look like a the waves on the surface of water, but all the motion is in the plane of your video monitor. The motion of the grid is perpendicular to the direction the wave propagates.

## 1. What are sound waves?

Sound waves are a type of energy that travel through a medium, such as air or water, as a series of compressions and rarefactions. These waves are created by vibrations and can be heard by the human ear.

## 2. How are sound waves propagated?

Sound waves are propagated as transverse waves, meaning that the particles of the medium vibrate perpendicular to the direction of the wave's motion. This allows the sound to travel through the medium in a series of up and down movements.

## 3. What is the difference between transverse and longitudinal waves?

Transverse waves, like sound waves, move perpendicular to the direction of the wave's motion. In contrast, longitudinal waves move parallel to the direction of the wave's motion, such as in a slinky. Sound waves are transverse waves, while seismic waves (earthquakes) are longitudinal waves.

## 4. Can sound waves travel through a vacuum?

No, sound waves cannot travel through a vacuum because they require a medium to vibrate and propagate. In a vacuum, there are no particles for the sound waves to interact with, resulting in no sound being produced.

## 5. How does the frequency of a sound wave affect its pitch?

The frequency of a sound wave is directly related to its pitch. Higher frequency sound waves have a higher pitch, while lower frequency sound waves have a lower pitch. This is because the frequency determines the number of vibrations per second, which our ears interpret as pitch.