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jaejoon89
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Homework Statement
How do you derive the divergence in cylindrical coordinates by transforming the expression for divergence in cartestian coordinates?
Homework Equations
F = F_x i + F_y j + F_z k
div F = ∂F_x/∂x + ∂F_y/∂y + ∂F_z/∂z (divergence in Cartesian coordinates)
I need to transform this into
divF = (1/rho)(∂(rho*F_rho)/∂rho) + (1/rho)(∂F_theta/∂theta) + ∂F_z/∂z (divergence in cylindrical coordinates)
The Attempt at a Solution
Using the chain rule,
∂F_x/∂x = (∂F_x/∂rho)(∂rho/∂x) + (∂F_x/∂theta)(∂theta/∂x) + (∂F_x/∂z)(∂z/∂x)
Similarly for F_y and F_z
Then I rewrite the cartesian definition for divergence and obtain
divF = [(∂F_x/∂rho)costheta + (∂F_x/∂theta)(-sintheta/rho)] + [(∂F_y/∂rho)sintheta + (∂F_y/∂theta)(costheta/rho)] + ∂F_z/∂z
But how does that simplify to the expression in cylindrical coordinates?