[LukeFullard]

Hi all,
I am interested in the fluid equations for flow of a fluid inside a pendulum. Just focusing on the x-y plane, and if I define y to be along the direction of the pendulum string (radial), and x to be perpendicular to that.

If the angle of the pendulum is theta, (theta = 0 when the pendulum is just hanging there vertical), then the components of gravity will be

gx=9.81*sin(theta)
gy=-9.81*cos(theta)

My question is, if the pendulum is swinging to and fro at some frequency and amplitude, there will be some acceleration in both the x and y directions to account for. How do I do this?

Thanks all