1. The problem statement, all variables and given/known data Gravity Waves. Consider a pattern of motion in which fluid elements move at an angle θ to the vertical. Show that for an atmosphere where the Brunt-Vaisala frequency is ωB the elements will oscillate with a frequency ν = N cos θ. 2. Relevant equations , -Brunt Vaisala frequency, g= gravity θ = potential temperature v= N cos θ -desired frequency of oscillation of the elements. N= Brunt Vaisala frequency θ = angle in rads (I know it's confusing here but wikipedia linked theta for potential temperature and I don't know how to make equations yet). 3. The attempt at a solution Is ωB supposed to be something? So I know that the Brunt-Vaisala frequency is the buoyancy frequency, is it just a frequency with respect to the vertical? In which case the answer is just to multiply N by cosθ? This could be it, but the part where they define N=ωB confuses me, though there is more to the question.