How do i convert a physics model into a simulink model?

Hello,

I have a control engineering problem.At the moment i am working on modelling a helium balloon. The forces that i have are : on the Y axis : Δρ*v*g-m*g=ma (Buoyancy force -weight)

Can someone tell me how can i turn this into a simulink model which i could potentially connect to a VRML environment ?

Thanks, Tom