# Velocity of flow in cylindrical coordinates [closed]

An infinitely long cylindrical bucket with radius $a$ is full of water and rotates with constant angular velocity $\Omega$ about its horizontal axis. The gravity is in the vertical direction. The velocity of the flow in cylindrical coordinates (whose $z$ axis is the horizontal axis of the bucket) is given by $\vec u = \left\langle {{u_r}(r,t),{u_\theta }(r,t),0} \right\rangle$.

Show that ${{u_r}(r,t)} = 0$.

I actually have no idea how to start. Any help will be appreciated.

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 Again, it's just the incompressibility condition – poorsod Oct 7 '12 at 23:11

## closed as too localized by David Zaslavsky♦Oct 8 '12 at 3:49

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