What limits the speed at which elastic materials contract or expand?
Answers
Suppose a material is fixed at one end and stretched with a force within its elastic limit (so no permanent deformation occurs), what happens internally when the force is instantaneously released? Even though the stress was uniformly spread along the material, presumably the molecules nearer the fixed point cannot instantaneously know that the force no longer exists at the other end. My intuition is that a wavefront occurs in the material, starting at the released end and propagating at the speed of sound (for the material), until it reaches the fixed end (and reflects?) - but I haven't been able to find any confirmation of this. Is this the case? And if so, does this limit the maximum contraction rate of the material to the speed of sound, or does the contraction rate depend upon other aspects of the material? The reason I'm asking is to try to get a better understanding of what the limiting factors are of a projectile being launched from an elastic material. Assuming the elastic energy is all converted to kinetic energy for the projectile, what limits the maximum launch speed?