Rolling ball on 3D surface

Hi,

For a school project I need to study the dynamic of a ball. I already finished the flight and bouncing dynamic but now I need to make it roll on any 3D surface using ode45.

I came with this idea :

function F = Roulement(t,Y)
P = Parametres() ;
g = P.gravite ;

n = normale(Y(1),Y(2),'terrain')
ez=[0,0,1]';


F = [Y(4);Y(5);Y(6);g*(n*ez)*n(1);g*(n*ez)*n(2);g*(n*ez)*n(3)-g];

Where normale return the normal vector for the point (Y(1),Y(2)) of the function terrain (the 3D surface), Roulement is the function that I will next give to ode45.

Of course it can't work because Y(1) and Y(2) are not scalars. So what should I do ?

Thanks

[James Tursa]

This really looks like a sliding point mass simulation, not a rolling ball simiulation. Why aren't Y(1) and Y(2) scalars? Do you have a 6-element state vector (3 position and 3 velocity)? Can you tell us more about how you have set this problem up?