CompuServe Messages

Hi, Kamron– Pressure waves (P-waves) are like sound – alternate compression and rarefaction of the medium. Solids, liquids and gases all expand when released from compression. Shear waves are side-to-side motions, like swinging one end of a garden hose side-to-side and seeing the wave of sideways motion traveling down the hose. Swing a bit of solid sideways, and it will pull the next bit of solid sideways, which will pull the next, and so on. Meanwhile the first bit of solid will generally "want" to snap back toward its original position (i.e., its effect on the farther bit of solid has a reaction). But a fluid can move sideways without the farther bits of fluid being much affected. Fluids have viscosity, but that is trivial compared to the connection between parts of a solid, and they do not snap back after a sideways motion – they will just stay where they were moved, on average. –Doug