public virtual void Enable(bool bImmovable, float mass)
        {
            //set whether the object can move
            Body.Immovable = bImmovable;
            //calculate the centre of mass
            Vector3 centerOfMass = SetMass(mass);

            //adjust skin so that it corresponds to the 3D mesh as drawn on screen
            Body.MoveTo(Transform3D.Translation, Matrix.Identity);
            //set the centre of mass
            Collision.ApplyLocalTransform(new Transform(-centerOfMass, Matrix.Identity));
            //enable so that any applied forces (e.g. gravity) will affect the object
            Body.EnableBody();
        }