# Stokes drag of oscillation sphere

1. Jul 12, 2011

### chaosma

If we consider a sphere oscillates in viscous fluid with frequency w,
then sphere has velocity u=$u_0*e^{-iwt}$

In Laudau's book, he defined the velocity of fluid is:
v=$e^{iwt}*F$
where F is a vector with only spatial variable involved.
The boundary condition then becomes $u=v$ at $|x|=R$,
where R is radius of sphere and origin is center of sphere.

My question is that this is a non-inertial frame, but Landau didn't introduce any
extra periodic force. Why is this true? Thank you!

2. Jul 13, 2011

### chaosma

I figured it out.
First, use non-inertial frame, write down the NS equation with velocity w.
Then let $u=w+u_0$
where $u_0$ is velocity of sphere.