I would like to start a discussion involving how sound works.

[ymalmsteen887]

How do you quote someone if you want to take a portion of what they said or like you did where you separated my sentences?

 

[JaredJames]

How do you quote someone if you want to take a portion of what they said or like you did where you separated my sentences?

Put [ QUOTE ] in front of what you want to quote and [ /QUOTE ] at the end (without the spaces).

 

[ymalmsteen887]

The particle then moves back past the original position and repeats the above, eventually slowing to a stop at it's original position.

Why does it have to move past the original postion. Why won't it just go back to the original postion and repeat?

 

[JaredJames]

Watch the top animation here (a sound wave): http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

Watch the molecules as they go from being under compression to expansion. This compression and expansion happens about their neutral (or equilibrium) positions - conservation of momentum.

 

[ymalmsteen887]

The red line isn't going behind the originall position. The molecules seem to be going back to their strating position.

 

[JaredJames]

OK, starting position obviously not the choice of word for you here. We'll go with equilibrium position.

The distance from the equilibrium position to the peak (maximum compression / expansion) is the amplitude.

Is that better for you?

 

[ymalmsteen887]

When you look at a sine wave you see displacement from the line in one direction(through) and then displacement the other direction(peak).

Lets say the line representing equilibrium is the center. Does it move one way away from the center and then on the way back move in the other direction away from the center, is that a full compression and expansion. Can you have compression without expansion?

 

[JaredJames]

Lets say the line representing equilibrium is the center.

The centre is the equilibrium point.

Does it move one way away from the center and then on the way back move in the other direction away from the center,

Yes - for a longitudinal wave represented on an oscilloscope as a sine wave. Transverse waves are slightly different (they are the ones that look like a sine wave).

Can you have compression without expansion?

So far as longitudinal waves go, I don't believe so.

 

[ymalmsteen887]

When friction is applied to moving objects they slow down but sound doesn't slow down what causes sound to cease?

 

[JaredJames]

When friction is applied to moving objects they slow down but sound doesn't slow down what causes sound to cease?

The amount of energy transferred to the next particle each time becomes less and less, so the displacement from the equilibrium position becomes smaller until eventually the amplitude becomes 0.

 

[ymalmsteen887]

When a guitar string vibrates doesn't it compress the air on one side and expand the air on another,thinking two dimensionaly, does this cause the sound to cancel? Wouldnt the compressed part of the wave wrap around to the expanded area?

 

[ymalmsteen887]

If you take a pendulum and push it will skip its resting position on the way back down this is easy to understand. The guitar string does the same thing but a speaker only moves from its resting poistion in one direction before returning to start over or is this wrong, I'm not sure?

 

[ymalmsteen887]

Is it only a wave if it has peaks and valleys? Can it not have just peaks or just valleys?
I guess to make it easier is it possible to have half a wave start but not finish? I'm thinking no.

 

[JaredJames]

Slow down, calm down.

When a guitar string vibrates doesn't it compress the air on one side and expand the air on another,thinking two dimensionaly, does this cause the sound to cancel? Wouldnt the compressed part of the wave wrap around to the expanded area?

No and no.

If you take a pendulum and push it will skip its resting position on the way back down this is easy to understand. The guitar string does the same thing but a speaker only moves from its resting poistion in one direction before returning to start over or is this wrong, I'm not sure?

Speakers move in and out.

Is it only a wave if it has peaks and valleys? Can it not have just peaks or just valleys?
I guess to make it easier is it possible to have half a wave start but not finish? I'm thinking no.

A wave doesn't need both.

 

[ymalmsteen887]

Slow down, calm down.


No and no.

I don't see how this can be if air pressure is at rest and you disturb ityou would be changing the pressure, so if the string pushes against the air it compresses it and the other side of the string should create an area of less pressure so the surrounding greater pressure should travel to the area of lower pressure.


Speakers move in and out.

What about the enclosures people use for speakers isn't it to affectively create pressure if you put more air in an air tight room it would increase the pressure inside the room but if there was anyway for the air to get out it wouldn't contribute, this is what I was saying about the guitar string as well. Check out this link it shows what I am talking about with the speaker and guitar string

http://paws.kettering.edu/~drussell/Demos/rad2/mdq.html look at the dipole source.


A wave doesn't need both.

Not sure what you mean do you think you could explain it in terms of a water wave. When you push down on water you are essentialy adding more voluume to it but it doesn't affect the entire body of water at once so it spreads out to do this so if you took youre hand in and out of the water you are making a wave. So the peaks of the wave would be when add to the water.So what would a valley(or expansion by comparison)be?

 

[JaredJames]

I don't see how this can be if air pressure is at rest and you disturb ityou would be changing the pressure, so if the string pushes against the air it compresses it and the other side of the string should create an area of less pressure so the surrounding greater pressure should travel to the area of lower pressure.

But that's not what you said initially.

What about the enclosures people use for speakers isn't it to affectively create pressure if you put more air in an air tight room it would increase the pressure inside the room but if there was anyway for the air to get out it wouldn't contribute, this is what I was saying about the guitar string as well. Check out this link it shows what I am talking about with the speaker and guitar string

http://paws.kettering.edu/~drussell/Demos/rad2/mdq.html look at the dipole source.

Not sure what you mean do you think you could explain it in terms of a water wave. When you push down on water you are essentialy adding more voluume to it but it doesn't affect the entire body of water at once so it spreads out to do this so if you took youre hand in and out of the water you are making a wave. So the peaks of the wave would be when add to the water.So what would a valley(or expansion by comparison)be?

A water wave is not the same as a sound wave. Do not confuse the two. One is transverse the other is longitudinal (I have asked you to read through the links).

Ignore the speaker stuff for now. Learn the basics - keep it simple.

 

[ymalmsteen887]

But that's not what you said initially.


A water wave is not the same as a sound wave. Do not confuse the two. One is transverse the other is longitudinal (I have asked you to read through the links).

Ignore the speaker stuff for now. Learn the basics - keep it simple.

Actually according to that link you gave me a water wave is bothe transverse and longitudinal.

 

[JaredJames]

Actually according to that link you gave me a water wave is bothe transverse and longitudinal.

You are describing a water wave as a sine wave - transverse wave. Sound is not a transverse wave and so you can't describe it the same way as water is displaced in peaks and troughs.

You can describe sound as it would be represented as a sine wave but can't compare the motion of water molecules to air particles.

 

[ymalmsteen887]

Ok here is what I know so far sound is a pressure wave which is molecules vibrating back and forth and the wave is measured by the distance between two compressed or expanded areas. Whats the next logical step before I can understand attenuation of different frequencies?

 

[Pythagorean]

Ok here is what I know so far sound is a pressure wave which is molecules vibrating back and forth and the wave is measured by the distance between two compressed or expanded areas. Whats the next logical step before I can understand attenuation of different frequencies?

Thermodynamics, maybe?

As the air molecules "pass the signal" to each other, they experience collisions with each other (which is how they transfer the information about the wave); they lose energy from these collisions and convert it to heat in their environment.

 

[ymalmsteen887]

You are describing a water wave as a sine wave - transverse wave. Sound is not a transverse wave and so you can't describe it the same way as water is displaced in peaks and troughs.

You can describe sound as it would be represented as a sine wave but can't compare the motion of water molecules to air particles.

Are you going to respond or are we finished here? I'm not impatient I just thought you were wating for me to ask another question cause I was asking for clarification on my last comment.

 

[JaredJames]

Ok here is what I know so far sound is a pressure wave which is molecules vibrating back and forth and the wave is measured by the distance between two compressed or expanded areas.

Correct

Whats the next logical step before I can understand attenuation of different frequencies?

As per pythagoreans response.

 

[ymalmsteen887]

Correct


As per pythagoreans response.

Well I mean can you explain it or are you telling me to read a book on it? I want to keep it simple right now.