The particles of a medium will settle the rest position after a mechanical wave passes.

"AT the rest position. Just like a spring no longer being moved, the material will return back to how it started.  

For any setup, we always have speed = v = √(F/μ), where F is the tension, stiffness, or some measure of resistance to being moved, and μ is the density (perhaps linear density or actual density depending on the setup), so the answer is DENSITY AND STIFFNESS"

-Bradley

conduction, convection, radiation

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