A paddle 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 paddle oscillates at ω=0.72 rad s−1\omega = 0.72\,\mathrm{rad\,s^{-1}} in a tank stratified so that N=1.2 rad s−1N = 1.2\,\mathrm{rad\,s^{-1}}. In one beam, the crests are photographed drifting steadily down and to the left, moving in a direction 53.1∘53.1^\circ below the horizontal. Someone argues: “Since the crests in this beam are moving down and to the left, the wave must be carrying its energy down and to the left as well.” ((a)) Find the true direction (quadrant and angle to the horizontal) of the energy flux in this beam. ((b)) Say whether the argument is correct, and why.

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