Falling ball

Hi,

I am trying to simulate a falling ball inside a fluid, this is for simulate a falling ball viscometer. I'm working in transient mode, with the sphere like "sliding wall" and the tube like "no slip", when I make the simulation with bigger dimensions it kind of works, but when i do it with the real dimensions, the simulation does not work.

I am not sure what is missing, I should take into account the gravity? If so, how should I do it?
The model is a tube with a sphere in the bottom, when I play the animation the fluid beggins to change near the sphere, but it doesn't reach all the fluid (the sphere never moves), I don't know how to simulate the falling ball in the fluid. How should I do it?

Thank you very much