Transverse and Longitudinal Sound Waves

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Discussion Overview

The discussion centers on the nature of sound waves, specifically the differences between longitudinal and transverse sound waves in various media, including gases, liquids, plasmas, and solids. Participants explore the conditions under which these waves propagate and the implications for different material structures, including crystalline and amorphous solids.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that sound waves are solely longitudinal in gases, liquids, and plasmas, while both longitudinal and transverse waves can propagate in solids.
  • Others argue that in crystalline solids, there are multiple wave types, including two transverse and one longitudinal wave.
  • A participant questions whether their understanding of sound wave propagation in different states of matter is mistaken, specifically regarding the ability of solids to support both wave types.
  • It is noted that fluids do not support shear stresses, which is a key factor in the inability of liquids to support transverse waves.
  • Some participants suggest that the structural bonds in solids, regardless of being crystalline or amorphous, enable shear stress and thus allow for transverse wave propagation.
  • A later reply emphasizes that displacing a liquid in a transverse direction does not result in energy change due to the absence of restoring forces, reinforcing the argument against transverse modes in fluids.

Areas of Agreement / Disagreement

Participants express differing views on the propagation of sound waves in various media, with no consensus reached on the specifics of how amorphous materials relate to transverse wave support.

Contextual Notes

Limitations include assumptions about the definitions of solids and the nature of shear stress, as well as the lack of resolution regarding the behavior of amorphous materials in relation to sound wave propagation.

narra
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What causes sound waves to be solely longitudinal in gas, liquid, and plasmas, but enables longitudinal and transverse in solids? Also, does solids only mean crystalline structures or are amorphous materials also able to support transverse sound waves?
 
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Hi,

Sound waves travels in all except perfect vacuum.
In crystals we have 3 waves (two transverse and one longitudinal waves)
 
I was of the understanding that only Longitudinal sound (Pressure) waves could propagate in gas, liquid, and plasma. Whereas in solids, both longitudinal and transverse sound waves were possible, and hence my first question. Am I mistaken?
 
Fluids don't support shear stresses. All solids do, so it shouldn't matter if they are amorphous or crystalline.
 
So it is the solids lattice (structural bonds) which promote shear stress, thus allowing lateral density modulation?
 
If you displace a section of a liquid in the transverse direction there is no change in the energy of the liquid, since no chemical bonds are being stretched. Thus there is no restoring force, and no transverse mode.
 

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