getting rigidbody to slide only on local z axes

I’m working on a ski simulator prototype. I have my skier rotating and sliding down slopes. I’m trying connect the dots by having my skier only move the direction he is facing when he is sliding down slopes. I am currently using the box collider ice material for motion.

Ok so i figured it out and realized how stupid this question is.

function FixedUpdate () {
rigidbody.AddRelativeForce (Vector3.forward * 10);
}