Transverse and Longitudinal Sound Waves

[narra]

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?

 

[Rajini]

Hi,

Sound waves travels in all except perfect vacuum.
In crystals we have 3 waves (two transverse and one longitudinal waves)

 

[narra]

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?

 

[johng23]

Fluids don't support shear stresses. All solids do, so it shouldn't matter if they are amorphous or crystalline.

 

[narra]

So it is the solids lattice (structural bonds) which promote shear stress, thus allowing lateral density modulation?

 

[luriol]

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.