WHat?

using UnityEngine;
using System.Collections;

public class ballBehavs : MonoBehaviour {

    int i;
    Rigidbody rb_me;

    // Use this for initialization
    void Start () {
        rb_me = GetComponent<Rigidbody> ();

    }

    // Update is called once per frame
    void Update () {

        if (Input.GetKey (KeyCode.W)) {
            rb_me.AddForce (transform.forward * i * Time.deltaTime);
            i++;
        } else {
            i = 0;
        }


    }


}