i did it :mrgreen:

i change the function add to the following:
[pascal]
function add(v1,v2: TVector): TVector;
begin
result.x:=v1.x/5 + v2.x;
result.y:=v1.y/5 + v2.y;
result.z:=v1.z/5 + v2.z;
end;
[/pascal]

then how to do a slide collision with a moving shpere and a static plane?
a plane have 5 vectors(include the center point), or?