- #1
norsktramp
- 4
- 0
Homework Statement
I'm an engineering student, and my professor of the mechanics course gave a homework to my class last week, we were intended to calculate the real shape of the Earth (as an ellipsoid) by taking the centrifugal force in account, using the equation [itex]a' = a -wX(wXr)[/itex]. For that, we also used Euler's equation [itex]∇p + ρg + ρa = 0 .[/itex] My professor then solved the problem considering Earth as a sphere, as I'm going to show it below. So my question is, how can I calculate the shape of the Earth (as an ellipsoid).
Variables and meaning : ∇p = gradient of pressure, a' = aceleration in a non inercial reference, w = angular velocity, g = gravity. (all of them are vectors)
Homework Equations
He told us that in a non inercial reference, the imaginary acelerations could be considered as a field aceleration, so he combined Euler's formula with the centrifugal force, by substituting it in the place of gravity. so we got:[tex]∇p -ρ[wX(wXr)] + ρa = 0.[/tex]
a = GM/r2 runitary = GM/r3 rvector,[tex]r^2 = x^2 + z^2[/tex].
considering w in the z axis we will obtain a relation for ∂p/∂x and ∂p/∂z, then we will solve the equation obtaining: [tex]p(x,z) = -ρGM/(√x^2 + z^2) -ρw^2*x^2/2 + C[/tex] C being a constant.
considering p as: [itex]p(0,R) = po = -ρGM/R + C[/itex], we obtain [itex]C = po + ρGM/R[/itex]
so [tex] p(x,z) = -ρGM/(√x^2 + z^2) -ρw^2*x^2/2 + po + ρGM/R[/tex]
To find the formula of the surface of the Earth we got to make p = po.
Now, making an assumption that w → 0 (not true for the earth), we will obtain [itex]ρGM/(√x^2 + z^2) = ρGM/R[/itex] [tex]x^2+z^2 = R^2[/tex] Obtaining a sphere equation.
The Attempt at a Solution
I want to know how to calculate the Earth's shape not considering w → 0, in a way I will obtain an ellipsoid. I also know a lot of things are mispelled and with a dificult to read format, but I ask for your patience and help. If you need any extra information please ask for it.