# Supersonic wave in a solid

by Clausius2
Tags: solid, supersonic, wave
 Sci Advisor PF Gold P: 1,479 Well guys, I was just referring to some proyectile penetrating supersonically (i.e. v>>c(solid)) into a solid. What is the difference with an aeroplane flying supersonically in the air?. In both mediums there will be elastic or plastic deformations transported via waves. The problem here is: will a solid's particle be deformed if the source of deformation (proyectile) goes faster than elastic wave speed?. Surely it will be deformed, but not in the classical way. My question is if all physical process involved with discontinuities (shock waves) in fluids are extensible for solids. (I'm sure it will be with another equations). The other question was: what is the role of light velocity in the propagation of deformations?. We always talk about sound velocity, but the real question is: Is it not curious that light velocity does not appear in the Wave Equation? (for elastic waves in a solid).
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PF Gold
P: 39,339
 Quote by Clausius2 Well guys, I was just referring to some proyectile penetrating supersonically (i.e. v>>c(solid)) into a solid. What is the difference with an aeroplane flying supersonically in the air?.
If that was what you were referring to, it certainly was NOT what you said!
You specifically asked about a wave traveling faster than the speed of sound in the solid. That is impossible by definition. It is, of course, possible for an object to move through a solid faster than the speed of sound (i.e. the natural wave speed) in that solid.

 In both mediums there will be elastic or plastic deformations transported via waves. The problem here is: will a solid's particle be deformed if the source of deformation (proyectile) goes faster than elastic wave speed?. Surely it will be deformed, but not in the classical way. My question is if all physical process involved with discontinuities (shock waves) in fluids are extensible for solids. (I'm sure it will be with another equations).
Yes, of course. There is a more extensive literature on shock waves (which travel at the speed of sound) in solids than in air.

 The other question was: what is the role of light velocity in the propagation of deformations?. We always talk about sound velocity, but the real question is: Is it not curious that light velocity does not appear in the Wave Equation? (for elastic waves in a solid).
Because "sound velocity" is DEFINED as the speed of propagation of deformations. I don't see why you would think that light velocity would have anything to do with it. As for "light velocity does not appear in the Wave Equation", the natural velocity of waves in the solid appears in the wave equation- that is, by definition, the "speed of sound" in that solid. The speed of light is the natural speed of electromagnetic waves in vacuum and has nothing to do with wave in solids.
 P: 55 In solids the velocity of sound is not unique, for example a shear wave will travel at a different velocity (higher) than a pure compression wave. As a matter of fact flexural waves do not have a well defined velocity as they are dispersive ... the frequency of the wave changes with displacement. Furthermore in two and three dimensional waves in solids the propagation area changes with distance so that a characteristic impedance cannot be defined and the wavelelength (but not the frequency) change during propagation. $$\therefore$$ you will need to define the type of wave in solid before you can ask if a faster wave is possible. Best