Longitudinal waves on a string

[zongo123]

Good day to everyone,

I kindly ask for your help. My question is: "Does a string have to be under tension, to transmit longitudinal waves? Why is it so?" I have trouble finding relevant scientific articles regarding the question and for reasearching "longitudinal waves on a string". If anyone knows a good source for studying this, please point at that direction.

Thank you! Have a nice day :)

 

[BvU]

Hello @zongo123 ,

!
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Your question is definitely valid. But I think you could come up with some arguments alll by yourself. Take a piece of rope, fix one end and experiment.

For waves to propagate, whether longitutinal or transverse, there has to be some kind of restoring force. It's hard to imagine a restoring force in the absence of any tension whatsoever.

Do you agree ?

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[A.T.]

Does a string have to be under tension, to transmit longitudinal waves?

Technically a material can transmit sound even without pretension. But this might not be what is meant by "longitudinal waves in a string". For example, in a string made of fibers the sound speed within the fiber material can be different than the longitudinal wave speed in the whole compound, where fibers change shape and move relative to each other.

 

[Arjan82]

What do you think is the difference between a sound wave and a longitudinal wave? And how can the sound speed within the material differ from that of a longitudinal wave? I would say they are the same thing.

 

[A.T.]

And how can the sound speed within the material differ from that of a longitudinal wave?

The question is about a "string" which is not a material. It is an object that can contain parts of various geometries and materials.

Consider the difference between the longitudinal wave propagating along the axis of a spring vs. the sound propagating in wire the spring is made of.

 

[Mister T]

I have been told that when playing a stringed instrument such as a guitar, players can cause longitudinal waves to propagate along a string when they slide their fingers along the string. You hear this as a note with a higher pitch because longitudinal waves propagate faster than transverse waves in a guitar spring.

 

[sophiecentaur]

The speed of longitudinal waves would certainly be a lot higher than transverse waves on a string so resonances would be a lot higher. The fact that the squeaks can be so loud would suggest that there could be resonances involved. (Those squeaks are only (afair) set up on the wound strings.)

Edit [ I suggest that the 'surface wave mode' could also exist (Thick and thin cross sections) - slower than straight compression wave but faster than transverse]

 

[rcgldr]

The Yamaha G12 midi guitar relies on longitudinal waves to measure distance from bridge to the fret the string is pressed against. Any transverse waves are ignored.