A cylinder oscillates at in a tank stratified so that

PHYSICS · Multi-part · Fermi University Physics · Oscillations, Waves & Acoustics · Fluids & Continuum Physics · Waves, acoustics and compressible flow

Signal Speeds in Fluids, Ch Internal gravity waves in a stratified fluid

Problem

A cylinder oscillates at ω=0.5 rad s−1\omega = 0.5\,\mathrm{rad\,s^{-1}} in a tank stratified so that N=1.0 rad s−1N = 1.0\,\mathrm{rad\,s^{-1}}, producing a St Andrew's cross. A schlieren photograph of the beam that extends into the upper right of the cross shows the lines of constant phase (crests) drifting steadily down and to the right, moving in a direction 60∘60^\circ below the horizontal. ((a)) State the direction (which quadrant, and the angle above or below the horizontal) in which wave energy travels along this beam. ((b)) Explain in one or two sentences why crests drifting downward in this beam does not mean that energy is carried downward there.

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